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1
Keirsbulck, L., L. Labraga, A. Mazouz und C. Tournier. „Surface Roughness Effects on Turbulent Boundary Layer Structures“. Journal of Fluids Engineering 124, Nr. 1 (15.10.2001): 127–35. http://dx.doi.org/10.1115/1.1445141.
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A turbulent boundary layer structure which develop over a k-type rough wall displays several differences with those found on a smooth surface. The magnitude of the wake strength depends on the wall roughness. In the near-wall region, the contribution to the Reynolds shear stress fraction, corresponding to each event, strongly depends on the wall roughness. In the wall region, the diffusion factors are influenced by the wall roughness where the sweep events largely dominate the ejection events. This trend is reversed for the smooth-wall. Particle Image Velocimetry technique (PIV) is used to obtain the fluctuating flow field in the turbulent boundary layer in order to confirm this behavior. The energy budget analysis shows that the main difference between rough- and smooth-walls appears near the wall where the transport terms are larger for smooth-wall. Vertical and longitudinal turbulent flux of the shear stress on both smooth and rough surfaces is compared to those predicted by a turbulence model. The present results confirm that any turbulence model must take into account the effects of the surface roughness.
2
Squire, D. T., N. Hutchins, C. Morrill-Winter, M. P. Schultz, J. C. Klewicki und I. Marusic. „Applicability of Taylor’s hypothesis in rough- and smooth-wall boundary layers“. Journal of Fluid Mechanics 812 (28.12.2016): 398–417. http://dx.doi.org/10.1017/jfm.2016.832.
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The spatial structure of smooth- and rough-wall boundary layers is examined spectrally at approximately matched friction Reynolds number ($\unicode[STIX]{x1D6FF}^{+}\approx 12\,000$). For each wall condition, temporal and true spatial descriptions of the same flow are available from hot-wire anemometry and high-spatial-range particle image velocimetry, respectively. The results show that over the resolved flow domain, which is limited to a streamwise length of twice the boundary layer thickness, true spatial spectra of smooth-wall streamwise and wall-normal velocity fluctuations agree, to within experimental uncertainty, with those obtained from time series using Taylor’s frozen turbulence hypothesis (Proc. R. Soc. Lond. A, vol. 164, 1938, pp. 476–490). The same applies for the streamwise velocity spectra on rough walls. For the wall-normal velocity spectra, however, clear differences are observed between the true spatial and temporally convected spectra. For the rough-wall spectra, a correction is derived to enable accurate prediction of wall-normal velocity length scales from measurements of their time scales, and the implications of this correction are considered. Potential violations to Taylor’s hypothesis in flows above perturbed walls may help to explain conflicting conclusions in the literature regarding the effect of near-wall modifications on outer-region flow. In this regard, all true spatial and corrected spectra presented here indicate structural similarity in the outer region of smooth- and rough-wall flows, providing evidence for Townsend’s wall-similarity hypothesis (The Structure of Turbulent Shear Flow, vol. 1, 1956).
3
Zhu, Xiaojue, Roberto Verzicco und Detlef Lohse. „Disentangling the origins of torque enhancement through wall roughness in Taylor–Couette turbulence“. Journal of Fluid Mechanics 812 (22.12.2016): 279–93. http://dx.doi.org/10.1017/jfm.2016.815.
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Direct numerical simulations (DNS) are performed to analyse the global transport properties of turbulent Taylor–Couette flow with inner rough wall up to Taylor number$Ta=10^{10}$. The dimensionless torque $Nu_{\unicode[STIX]{x1D714}}$ shows an effective scaling of $Nu_{\unicode[STIX]{x1D714}}\propto Ta^{0.42\pm 0.01}$, which is steeper than the ultimate regime effective scaling $Nu_{\unicode[STIX]{x1D714}}\propto Ta^{0.38}$ seen for smooth inner and outer walls. It is found that at the inner rough wall, the dominant contribution to the torque comes from the pressure forces on the radial faces of the rough elements; while viscous shear stresses on the rough surfaces contribute little to $Nu_{\unicode[STIX]{x1D714}}$. Thus, the log layer close to the rough wall depends on the roughness length scale, rather than on the viscous length scale. We then separate the torque contributed from the smooth inner wall and the rough outer wall. It is found that the smooth wall torque scaling follows $Nu_{s}\propto Ta_{s}^{0.38\pm 0.01}$, in excellent agreement with the case where both walls are smooth. In contrast, the rough wall torque scaling follows $Nu_{r}\propto Ta_{r}^{0.47\pm 0.03}$, very close to the pure ultimate regime scaling $Nu_{\unicode[STIX]{x1D714}}\propto Ta^{1/2}$. The energy dissipation rate at the wall of an inner rough cylinder decreases significantly as a consequence of the wall shear stress reduction caused by the flow separation at the rough elements. On the other hand, the latter shed vortices in the bulk that are transported towards the outer cylinder and dissipated. Compared to the purely smooth case, the inner wall roughness renders the system more bulk dominated and thus increases the effective scaling exponent.
4
Underwood, B. Y. „Random-walk modeling of turbulent impaction to a smooth wall“. International Journal of Multiphase Flow 19, Nr. 3 (Juni 1993): 485–500. http://dx.doi.org/10.1016/0301-9322(93)90062-y.
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5
Schultz, Michael P., und Karen A. Flack. „Turbulent Boundary Layers Over Surfaces Smoothed by Sanding“. Journal of Fluids Engineering 125, Nr. 5 (01.09.2003): 863–70. http://dx.doi.org/10.1115/1.1598992.
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Flat-plate turbulent boundary layer measurements have been made on painted surfaces, smoothed by sanding. The measurements were conducted in a closed return water tunnel, over a momentum thickness Reynolds number Reθ range of 3000 to 16,000, using a two-component laser Doppler velocimeter (LDV). The mean velocity and Reynolds stress profiles are compared with those for smooth and sandgrain rough walls. The results indicate an increase in the boundary layer thickness (δ) and the integral length scales for the unsanded, painted surface compared to a smooth wall. More significant increases in these parameters, as well as the skin-friction coefficient Cf were observed for the sandgrain surfaces. The sanded surfaces behave similarly to the smooth wall for these boundary layer parameters. The roughness functions ΔU+ for the sanded surfaces measured in this study agree within their uncertainty with previous results obtained using towing tank tests and similarity law analysis. The present results indicate that the mean profiles for all of the surfaces collapse well in velocity defect form. The Reynolds stresses also show good collapse in the overlap and outer regions of the boundary layer when normalized with the wall shear stress.
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Jingbo, Su, Zhu Feng, Geng Ying und Ni Xingye. „Numerical Study of Wave Overtopping Based on Local Method of Approximate Particular Solution Method“. Advances in Mechanical Engineering 6 (01.01.2014): 541717. http://dx.doi.org/10.1155/2014/541717.
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In order to study the wave overtopping process, this paper establishes a two-dimensional numerical wave flume based on a meshless algorithm, local method of approximate particular solution (the LMAPS method), and the technology of momentum source wave. It calculates the climbing and overtopping process under regular waves on a typical slope, results of which are more consistent with the physical model test results. Finally, wave action simulation is carried out on six different structural forms of wave walls (vertical wave wall, 1/4 arc wave wall, reversed-arc wave wall, smooth surface wave wall with 1: 3 slope ratio, smooth surface wave wall with 1: 1.5 slope ratio and stepped surface wave wall with 1: 1.5 slope ratio). Numerical results of the simulation accurately describe the wave morphological changes in the interaction of waves and different structural forms of wave walls, in which, average error of wave overtopping is roughly 6.2% compared with the experimental values.
7
Boutouyrie, Pierre, Saliha Boumaza, Pascal Challande, Patrick Lacolley und Stéphane Laurent. „Smooth Muscle Tone and Arterial Wall Viscosity“. Hypertension 32, Nr. 2 (August 1998): 360–64. http://dx.doi.org/10.1161/01.hyp.32.2.360.
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8
Selvan, Krishnasamy T., und M. Sreenivasan. „An octave-band smooth-wall pyramidal horn“. Microwave and Optical Technology Letters 48, Nr. 4 (2006): 691–93. http://dx.doi.org/10.1002/mop.21444.
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9
Leonardi, S., P. Orlandi, L. Djenidi und R. A. Antonia. „Heat transfer in a turbulent channel flow with square bars or circular rods on one wall“. Journal of Fluid Mechanics 776 (13.07.2015): 512–30. http://dx.doi.org/10.1017/jfm.2015.344.
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Direct numerical simulations (DNS) are carried out to study the passive heat transport in a turbulent channel flow with either square bars or circular rods on one wall. Several values of the pitch (${\it\lambda}$) to height ($k$) ratio and two Reynolds numbers are considered. The roughness increases the heat transfer by inducing ejections at the leading edge of the roughness elements. The amounts of heat transfer and mixing depend on the separation between the roughness elements, an increase in heat transfer accompanying an increase in drag. The ratio of non-dimensional heat flux to the non-dimensional wall shear stress is higher for circular rods than square bars irrespectively of the pitch to height ratio. The turbulent heat flux varies within the cavities and is larger near the roughness elements. Both momentum and thermal eddy diffusivities increase relative to the smooth wall. For square cavities (${\it\lambda}/k=2$) the turbulent Prandtl number is smaller than for a smooth channel near the wall. As ${\it\lambda}/k$ increases, the turbulent Prandtl number increases up to a maximum of 2.5 at the crests plane of the square bars (${\it\lambda}/k=7.5$). With increasing distance from the wall, the differences with respect to the smooth wall vanish and at three roughness heights above the crests plane, the turbulent Prandtl number is essentially the same for smooth and rough walls.
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Wang, D. M., und J. M. Tarbell. „Modeling Interstitial Flow in an Artery Wall Allows Estimation of Wall Shear Stress on Smooth Muscle Cells“. Journal of Biomechanical Engineering 117, Nr. 3 (01.08.1995): 358–63. http://dx.doi.org/10.1115/1.2794192.
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The arterial media is modeled as a periodic array of cylindrical smooth muscle cells residing in a matrix comprised of proteoglycan and collagen fibers. Using Brinkman’s model to describe transmural flow through such a fibrous media, we calculate the effective hydraulic permeability of the media and the wall shear stress on smooth muscle cells. Two interesting results are obtained: first, the wall shear stress on smooth muscle cells is on the order of 1 dyne/cm2, which is in the range known to affect endothelial cells in vitro; second, the flow resistance due to smooth muscle cells is not negligible compared to the resistance due to the fiber matrix.
11
Hirota, M., H. Fujita und H. Yokosawa. „Experimental Study on Convective Heat Transfer for Turbulent Flow in a Square Duct With a Ribbed Rough Wall (Characteristics of Mean Temperature Field)“. Journal of Heat Transfer 116, Nr. 2 (01.05.1994): 332–40. http://dx.doi.org/10.1115/1.2911405.
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This paper presents experimental results concerning a time-mean temperature field obtained in forced convection heat transfer for a turbulent flow through a square duct with a ribbed rough bottom wall. The secondary flow pattern in the duct is reflected in the distribution of the local Nusselt number, the values of which on the smooth walls of the rough duct are 1.71~1.97 times those of the smooth duct. In the upper half cross section near the upper smooth wall opposite the bottom ribbed rough wall, the profile of the mean temperature distribution is similar to that of the primary flow velocity distribution, and the validity of the temperature inner law was confirmed. However, in the lower half cross section near the bottom ribbed rough wall, the dissimilarity between the mean velocity and the mean temperature fields becomes pronounced, and the inner law is not valid for mean temperature distributions. The mechanism of the heat transfer near the ribbed rough wall was examined based on the transport equations of turbulent shear stress and turbulent heat flux.
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Squire, D. T., C. Morrill-Winter, N. Hutchins, M. P. Schultz, J. C. Klewicki und I. Marusic. „Comparison of turbulent boundary layers over smooth and rough surfaces up to high Reynolds numbers“. Journal of Fluid Mechanics 795 (14.04.2016): 210–40. http://dx.doi.org/10.1017/jfm.2016.196.
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Turbulent boundary layer measurements above a smooth wall and sandpaper roughness are presented across a wide range of friction Reynolds numbers, ${\it\delta}_{99}^{+}$, and equivalent sand grain roughness Reynolds numbers, $k_{s}^{+}$ (smooth wall: $2020\leqslant {\it\delta}_{99}^{+}\leqslant 21\,430$, rough wall: $2890\leqslant {\it\delta}_{99}^{+}\leqslant 29\,900$; $22\leqslant k_{s}^{+}\leqslant 155$; and $28\leqslant {\it\delta}_{99}^{+}/k_{s}^{+}\leqslant 199$). For the rough-wall measurements, the mean wall shear stress is determined using a floating element drag balance. All smooth- and rough-wall data exhibit, over an inertial sublayer, regions of logarithmic dependence in the mean velocity and streamwise velocity variance. These logarithmic slopes are apparently the same between smooth and rough walls, indicating similar dynamics are present in this region. The streamwise mean velocity defect and skewness profiles each show convincing collapse in the outer region of the flow, suggesting that Townsend’s (The Structure of Turbulent Shear Flow, vol. 1, 1956, Cambridge University Press.) wall-similarity hypothesis is a good approximation for these statistics even at these finite friction Reynolds numbers. Outer-layer collapse is also observed in the rough-wall streamwise velocity variance, but only for flows with ${\it\delta}_{99}^{+}\gtrsim 14\,000$. At Reynolds numbers lower than this, profile invariance is only apparent when the flow is fully rough. In transitionally rough flows at low ${\it\delta}_{99}^{+}$, the outer region of the inner-normalised streamwise velocity variance indicates a dependence on $k_{s}^{+}$ for the present rough surface.
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El-Husayni, H. A., M. E. Taslim und D. M. Kercher. „Experimental Heat Transfer Investigation of Stationary and Orthogonally Rotating Asymmetric and Symmetric Heated Smooth and Turbulated Channels“. Journal of Turbomachinery 116, Nr. 1 (01.01.1994): 124–32. http://dx.doi.org/10.1115/1.2928266.
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An experimental investigation was conducted to determine the effects of variations in wall thermal boundary conditions on local heat transfer coefficients in stationary and orthogonally rotating smooth wall and two opposite-wall turbulated square channels. Results were obtained for three distributions of uniform wall heat flux: asymmetric, applied to the primary wall only; symmetric, applied to two opposite walls only; and fully symmetric, applied to all four channel walls. Measured stationary and rotating smooth channel average heat transfer coefficients at channel location L/Dh = 9.53 were not significantly sensitive to wall heat flux distributions. Trailing side heat transfer generally increased with Rotation number, whereas the leading wall results showed a decreasing trend at low Rotation numbers to a minimum and then an increasing trend with further increase in Rotation number. The stationary turbulated wall heat transfer coefficients did not vary markedly with the varaitions in wall heat flux distributions. Rotating leading wall heat transfer decreased with Rotation number and showed little sensitivity to heat flux distributions except for the fully symmetric heated wall case at the highest Reynolds number tested. Trailing wall heat transfer coefficients were sensitive to the thermal wall distributions generally at all Reynolds numbers tested and particularly with increasing Rotation number. While the asymmetric case showed a slight deficit in trailing wall heat transfer coefficients due to rotation, the symmetric case indicated little change, whereas the fully symmetric case exhibited an enhancement.
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SHAFI, H. S., und R. A. ANTONIA. „Small-scale characteristics of a turbulent boundary layer over a rough wall“. Journal of Fluid Mechanics 342 (10.07.1997): 263–93. http://dx.doi.org/10.1017/s0022112097005612.
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Measurements of the spanwise and wall-normal components of vorticity and their constituent velocity derivative fluctuations have been made in a turbulent boundary layer over a mesh-screen rough wall using a four-hot-wire vorticity probe. The measured spectra and variances of vorticity and velocity derivatives have been corrected for the effect of spatial resolution. The high-wavenumber behaviour of the spectra conforms closely with isotropy. Over most of the outer layer, the normalized magnitudes of the velocity derivative variances differ significantly from those over a smooth wall layer. The differences are such that the variances are much more nearly isotropic over the rough wall than on the smooth wall. This behaviour is consistent with earlier observations that the large-scale structure in this rough wall layer is more isotropic than that in a smooth wall layer. Isotropy-based approximations for the mean energy dissipation rate and mean enstrophy are consequently more reliable in this rough wall layer than in a smooth wall layer. In the outer layer, the vorticity variances are slightly larger than those over a smooth wall; reflecting structural differences between the two flows.
15
Kukreja, R. T., C. W. Park und S. C. Lau. „Heat (Mass) Transfer in a Rotating Two-Pass Square Channel — Part II: Local Transfer Coefficient, Smooth Channel“. International Journal of Rotating Machinery 4, Nr. 1 (1998): 1–15. http://dx.doi.org/10.1155/s1023621x98000013.
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Naphthalene sublimation technique and the heat/mass transfer analogy are used to determine the detailed local heat/mass transfer distributions on the leading and trailing walls of a twopass square channel with smooth walls that rotates about a perpendicular axis. Since the variation of density is small in the flow through the channel, buoyancy effect is negligible. Results show that, in both the stationary and rotating channel cases, very large spanwise variations of the mass transfer exist in he turn and in the region immediately downstream of the turn in the second straight pass. In the first straight pass, the rotation-induced Coriolis forces reduce the mass transfer on the leading wall and increase the mass transfer on the trailing wall. In the turn, rotation significantly increases the mass transfer on the leading wall, especially in the upstream half of the turn. Rotation also increases the mass transfer on the trailing wall, more in the downstream half of the turn than in the upstream half of the turn. Immediately downstream of the turn, rotation causes the mass transfer to be much higher on the trailing wall near the downstream corner of the tip of the inner wall than on the opposite leading wall. The mass transfer in the second pass is higher on the leading wall than on the trailing wall. A slower flow causes higher mass transfer enhancement in the turn on both the leading and trailing walls.
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Vreman, A. W. „Turbulence attenuation in particle-laden flow in smooth and rough channels“. Journal of Fluid Mechanics 773 (20.05.2015): 103–36. http://dx.doi.org/10.1017/jfm.2015.208.
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Results of point-particle direct numerical simulations of downward gas–solid flow in smooth and rough vertical channels are presented. Two-way coupling and inter-particle collisions are included. The rough walls are shaped as fixed layers of tiny spherical particles with diameter much smaller than the viscous wall unit. The turbulence attenuation induced by the free solid particles in the gas flow is shown to be enhanced with increasing wall roughness. The so-called feedback force, the force exerted by the free particles on the gas, is decomposed into three contributions: the domain average of the mean feedback force, the non-uniform part of the mean feedback force and the fluctuating part of the feedback force. Since the non-uniformity of the mean feedback force increases with wall roughness, the effect of the non-uniform part of the mean feedback force is investigated in detail. For both smooth and rough walls, the non-uniform part of the mean feedback force is shown to contribute significantly to the particle-induced turbulence attenuation.
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Zhu, Xiaojue, Rodolfo Ostilla-Mónico, Roberto Verzicco und Detlef Lohse. „Direct numerical simulation of Taylor–Couette flow with grooved walls: torque scaling and flow structure“. Journal of Fluid Mechanics 794 (06.04.2016): 746–74. http://dx.doi.org/10.1017/jfm.2016.179.
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We present direct numerical simulations of Taylor–Couette flow with grooved walls at a fixed radius ratio ${\it\eta}=r_{i}/r_{o}=0.714$ with inner cylinder Reynolds number up to $Re_{i}=3.76\times 10^{4}$, corresponding to Taylor number up to $Ta=2.15\times 10^{9}$. The grooves are axisymmetric V-shaped obstacles attached to the wall with a tip angle of 90°. Results are compared to the smooth wall case in order to investigate the effects of grooves on Taylor–Couette flow. We focus on the effective scaling laws for the torque, flow structures, and boundary layers. It is found that, when the groove height is smaller than the boundary layer thickness, the torque is the same as that of the smooth wall cases. With increasing $Ta$, the boundary layer thickness becomes smaller than the groove height. Plumes are ejected from the tips of the grooves and secondary circulations between the latter are formed. This is associated with a sharp increase of the torque, and thus the effective scaling law for the torque versus $Ta$ becomes much steeper. Further increasing $Ta$ does not result in an additional slope increase. Instead, the effective scaling law saturates to the ‘ultimate’ regime effective exponents seen for smooth walls. It is found that even though after saturation the slope is the same as for the smooth wall case, the absolute value of torque is increased, and more so with the larger size of the grooves.
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Wu, Sicong, Kenneth T. Christensen und Carlos Pantano. „Modelling smooth- and transitionally rough-wall turbulent channel flow by leveraging inner–outer interactions and principal component analysis“. Journal of Fluid Mechanics 863 (29.01.2019): 407–53. http://dx.doi.org/10.1017/jfm.2018.899.
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Direct numerical simulations (DNS) of turbulent channel flow over rough surfaces, formed from hexagonally packed arrays of hemispheres on both walls, were performed at friction Reynolds numbers $Re_{\unicode[STIX]{x1D70F}}=200$, $400$ and $600$. The inner normalized roughness height $k^{+}=20$ was maintained for all Reynolds numbers, meaning all flows were classified as transitionally rough. The spacing between hemispheres was varied within $d/k=2$–$4$. The statistical properties of the rough-wall flows were contrasted against a complementary smooth-wall DNS at $Re_{\unicode[STIX]{x1D70F}}=400$ and literature data at $Re_{\unicode[STIX]{x1D70F}}=2003$ revealing strong modifications of the near-wall turbulence, although the outer-layer structure was found to be qualitatively consistent with smooth-wall flow. Amplitude modulation (AM) analysis was used to explore the degree of interaction between the flow in the roughness sublayer and that of the outer layer utilizing all velocity components. This analysis revealed stronger modulation effects, compared to smooth-wall flow, on the near-wall small-scale fluctuations by the larger-scale structures residing in the outer layer irrespective of roughness arrangement and Reynolds number. A predictive inner–outer model based on these interactions, and exploiting principal component analysis (PCA), was developed to predict the statistics of higher-order moments of all velocity fluctuations, thus addressing modelling of anisotropic effects introduced by roughness. The results show excellent agreement between the predicted near-wall statistics up to fourth-order moments compared to the original statistics from the DNS, which highlights the utility of the PCA-enhanced AM model in generating physics-based predictions in both smooth- and rough-wall turbulence.
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Bank, Alan J. „Physiologic Aspects of Drug Therapy and Large Artery Elastic Properties“. Vascular Medicine 2, Nr. 1 (Februar 1997): 44–50. http://dx.doi.org/10.1177/1358863x9700200107.
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Vasoactive drugs alter smooth muscle tone not only in arterial resistance vessels, but also in large conduit arteries. The resultant changes in smooth muscle tone alter both conduit vessel size and stiffness and hence influence pulsatile components of left ventricular afterload. The effects of smooth muscle relaxation and contraction on arterial elastic properties are complex and have not been fully characterized. Several recent studies have utilized a new intravascular ultrasound technique to study the effects of changes in smooth muscle tone on brachial artery elastic mechanics in normal human subjects in vivo. Smooth muscle relaxation with nitroglycerin improves isobaric brachial artery compliance without significantly altering arterial wall stiffness as measured by incremental elastic modulus ( Einc). The improvement in compliance with smooth muscle relaxation is the net result of factors that: (1) increase wall stiffness (increased tension in parallel elastin and collagen fibers); (2) decrease wall stiffness (decreased tension in the smooth muscle and its associated series elastic component); and (3) increase vessel lumen size. Using a modified Maxwell model for the arterial wall, smooth muscle relaxation is also shown to shift the predominant elements contributing to wall stress and EInc from smooth muscle and the collagen fibers in series with the smooth muscle to collagen fibers in parallel with the smooth muscle. A better understanding of the mechanisms contributing to changes in arterial elastic mechanics following alterations in smooth muscle tone will help in developing pharmacologic therapies aimed at reducing pulsatile components of left ventricular afterload.
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VOLINO, R. J., M. P. SCHULTZ und K. A. FLACK. „Turbulence structure in rough- and smooth-wall boundary layers“. Journal of Fluid Mechanics 592 (14.11.2007): 263–93. http://dx.doi.org/10.1017/s0022112007008518.
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Turbulence measurements for rough-wall boundary layers are presented and compared to those for a smooth wall. The rough-wall experiments were made on a woven mesh surface at Reynolds numbers approximately equal to those for the smooth wall. Fully rough conditions were achieved. The present work focuses on turbulence structure, as documented through spectra of the fluctuating velocity components, swirl strength, and two-point auto- and cross-correlations of the fluctuating velocity and swirl. The present results are in good agreement, both qualitatively and quantitatively, with the turbulence structure for smooth-wall boundary layers documented in the literature. The boundary layer is characterized by packets of hairpin vortices which induce low-speed regions with regular spanwise spacing. The same types of structure are observed for the rough- and smooth-wall flows. When the measured quantities are normalized using outer variables, some differences are observed, but quantitative similarity, in large part, holds. The present results support and help to explain the previously documented outer-region similarity in turbulence statistics between smooth- and rough-wall boundary layers.
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Jou, D., A. Sellitto und F. X. Alvarez. „Heat waves and phonon–wall collisions in nanowires“. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 467, Nr. 2133 (23.03.2011): 2520–33. http://dx.doi.org/10.1098/rspa.2010.0645.
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The dispersion relation of heat waves along nanowires is obtained, displaying the influence of the roughness of the walls. This knowledge may be useful for the development of new experimental techniques based on heat waves, complementary to current steady-state measurements, for the exploration of phonon–wall collisions in smooth and rough walls.
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Privett, Diane W., und Rita L. Hummel. „Root and Shoot Growth of ‘Coral Beauty’ Cotoneaster and Leyland Cypress Produced in Porous and Nonporous Containers“. Journal of Environmental Horticulture 10, Nr. 3 (01.09.1992): 133–36. http://dx.doi.org/10.24266/0738-2898-10.3.133.
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Abstract ‘Coral Beauty’ cotoneaster and Leyland cypress rooted cuttings were grown in media of all fir bark or fir bark:peat moss (1:1 by vol) and plastic containers with varying wall designs (nonporous smooth-walls, nonporous ridge-walls, or porous walls). Results Indicated no effect of the growing media shoot or root growth of either species. Shoot growth of Leyland cypress was not affected by container design. ‘Coral Beauty’ cotoneaster shoot growth was greater in the porous container than in the nonporous smooth-walled container. Root Circling of both species was greatest in the nonporous smooth-walled containers. Ridges in the nonporous ridge-wall containers generally directed roots to grow downward where some circling at the bottom of the root ball occurred. When roots in the porous walled containers reached the periphery of the root ball they stopped growing, resulting in a fine, fibrous root mass at the periphery of the rootball.
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Han, J. C., Y. M. Zhang und C. P. Lee. „Influence of Surface Heat Flux Ratio on Heat Transfer Augmentation in Square Channels With Parallel, Crossed, and V-Shaped Angled Ribs“. Journal of Turbomachinery 114, Nr. 4 (01.10.1992): 872–80. http://dx.doi.org/10.1115/1.2928042.
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The effect of wall heat flux ratio on the local heat transfer augmentation in a square channel with two opposite in-line ribbed walls was investigated for Reynolds numbers from 15,000 to 80,000. The square channel composed of ten isolated copper sections has a length-to-hydraulic diameter ratio (L/D) of 20. The rib height-to-hydraulic diameter ratio (e/D) is 0.0625 and the rib pitch-to-height ratio (P/e) equals 10. Six ribbed side to smooth side wall heat flux ratios (Case 1—q″r1/q″s = q″r2/q″s = 1; Case 2—q″r1/q″s = q″r2/q″s = 3; Case 3—q″r1/q″s = q″r2/q″s = 6; Case 4—q″r1/q″s = 6 and q″r2/q″s = 4; Case 5—q″r1/q″s = q″r2/q″s = ∞; Case 6—q″r1/q″s = ∞ and q″r2/q″s = 0) were studied for four rib orientations (90 deg rib, 60 deg parallel rib, 60 deg crossed rib, and 60 deg V-shaped rib). The results show that the ribbed side wall heat transfer augmentation increases with increasing ribbed side to smooth side wall heat flux ratios, but the reverse is true for the smooth side wall heat transfer augmentation. The average heat transfer augmentation of the ribbed side and smooth side wall decreases slightly with increasing wall heat flux ratios. Two ribbed side wall heating (Case 5—q″r1/q″s = q″r2/q″s = ∞) provides a higher ribbed side wall heat transfer augmentation than the four-wall uniform heating (Case 1—q″r1/q″s = q″r2/q″s = 1). The effect of wall heat flux ratio reduces with increasing Reynolds numbers. The results also indicate that the 60 deg V-shaped rib and 60 deg parallel rib perform better than the 60 deg crossed rib and 90 deg rib, regardless of wall heat flux ratio and Reynolds number.
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Bariska, Mihály, Zoltán Pásztory und Zoltán Börcsök. „On tylosis ultrastructure in Quercus cerris L.“ Holzforschung 73, Nr. 12 (26.11.2019): 1121–23. http://dx.doi.org/10.1515/hf-2019-0028.
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Abstract A study of tylosis in European Turkey oak (Quercus cerris L.) shows correspondences in the formation of tyloses and of regular cell walls. The outer tylosis wall has a smooth, granular surface with simple perforations analogous to that of the primary wall of ordinary cells. The underlying wall stratum shows parallel oriented macro-fibrils, normally found in the secondary walls of regular cells. At the contact areas of tyloses, stabilizing seams can be observed. Various types of wall openings such as simple pits, blind pits and vestured pits were present. Also tylosis division was detected. The characteristics of parenchyma cell walls can be re-discovered in tyloses.
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Lee, S. W., H. S. Ahn und S. C. Lau. „Heat (Mass) Transfer Distribution in a Two-Pass Trapezoidal Channel With a 180deg Turn“. Journal of Heat Transfer 129, Nr. 11 (08.03.2007): 1529–37. http://dx.doi.org/10.1115/1.2764084.
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The heat transfer characteristics of airflows in serpentine cooling channels in stator vanes of gas turbines were studied. The cooling channels were modeled as a two-pass trapezoidal channel with a 180deg turn. Naphthalene sublimation experiments were conducted and the heat and mass transfer analogy was applied to study the local heat (mass) transfer distributions on one of the two primary walls of the channel. Results were obtained for turbulent airflow through the channel with smooth walls, and with transverse ribs on one wall and on two opposite walls, over a range of Reynolds numbers between about 10,000 and 60,000. The results showed that there was a very large variation of the local heat (mass) transfer distribution in the turn and downstream of the turn. In all of the cases studied, the regional average heat (mass) transfer was higher on the downstream half of the turn than on the upstream half of the turn and was higher in the turn with the flow entering the channel through the smaller straight section than when the flow was reversed. The shape of the local heat (mass) transfer distribution at the turn was not significantly affected by varying the air mass flow rate. In the smooth wall case, the local heat (mass) transfer was high near the end wall and the downstream outer wall in the turn and was relatively low in two regions near the upstream outer wall and the downstream edge at the tip of the divider wall in the turn. With ribs on two opposite walls, the variation of the local heat (mass) transfer was larger, especially in the turn and downstream of the turn, than in the smooth wall case. The pressure drop across the turn was higher in the case of the flow entering the channel through the larger straight section than when the flow was reversed. As expected, the ribs increased the pressure drop across the turn.
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Богомолов, Дмитрий, Dmitriy Bogomolov, Валерий Порошин, Valeriy Poroshin, Валентин Нижник und Valentin Nizhnik. „Mathematical model of heat flux in continuous media in thin 2d channel with moving rough wall.“ Bulletin of Bryansk state technical university 2014, Nr. 4 (05.12.2014): 100–108. http://dx.doi.org/10.12737/23096.
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The mathematical model of heat flux in continuous media in thin channel with moving rough wall in 2D approach is described.. The results of the comparisons of flow factors and Mussel numbers in channels with smooth walls and channels with real stochastic wall roughness are shown. Both static and dynamic cases were investigated.
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Seckin, Galip, Neslihan Seckin und Recep Yurtal. „Boundary shear stress analysis in smooth rectangular channels“. Canadian Journal of Civil Engineering 33, Nr. 3 (01.03.2006): 336–42. http://dx.doi.org/10.1139/l05-110.
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This study reports on experiments concerning the boundary shear stress and boundary shear force distributions in a smooth rectangular flume. Nonlinear regression-based equations are derived from experimental analysis to give the percentage of the total shear force carried by the walls and mean wall and bed shear stresses around the wetted perimeter as functions of the ratio of channel width to channel depth.Key words: boundary shear, shear force, open channel flow.
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Clark, Gabrielle L., Anastassia P. Pokutta-Paskaleva, Dylan J. Lawrence, Sarah H. Lindsey, Laurephile Desrosiers, Leise R. Knoepp, Carolyn L. Bayer, Rudolph L. Gleason und Kristin S. Miller. „Smooth muscle regional contribution to vaginal wall function“. Interface Focus 9, Nr. 4 (14.06.2019): 20190025. http://dx.doi.org/10.1098/rsfs.2019.0025.
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Pelvic organ prolapse is characterized as the descent of the pelvic organs into the vaginal canal. In the USA, there is a 12% lifetime risk for requiring surgical intervention. Although vaginal childbirth is a well-established risk factor for prolapse, the underlying mechanisms are not fully understood. Decreased smooth muscle organization, composition and maximum muscle tone are characteristics of prolapsed vaginal tissue. Maximum muscle tone of the vaginal wall was previously investigated in the circumferential or axial direction under uniaxial loading; however, the vaginal wall is subjected to multiaxial loads. Further, the contribution of vaginal smooth muscle basal (resting) tone to mechanical function remains undetermined. The objectives of this study were to determine the contribution of smooth muscle basal and maximum tone to the regional biaxial mechanical behaviour of the murine vagina. Vaginal tissue from C57BL/6 mice was subjected to extension–inflation protocols ( n = 10) with and without basal smooth muscle tone. Maximum tone was induced with KCl under various circumferential ( n = 5) and axial ( n = 5) loading conditions. The microstructure was visualized with multiphoton microscopy ( n = 1), multiaxial histology ( n = 4) and multiaxial immunohistochemistry ( n = 4). Smooth muscle basal tone decreased material stiffness and increased anisotropy. In addition, maximum vaginal tone was decreased with increasing intraluminal pressures. This study demonstrated that vaginal muscle tone contributed to the biaxial mechanical response of murine vaginal tissue. This may be important in further elucidating the underlying mechanisms of prolapse, in order to improve current preventative and treatment strategies.
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Plaum, Burkhard. „Optimization of Broadband Smooth-Wall Circular Horn Antennas“. Journal of Infrared, Millimeter, and Terahertz Waves 39, Nr. 10 (28.06.2018): 984–95. http://dx.doi.org/10.1007/s10762-018-0510-6.
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Bény, Jean-Louis. „Information Networks in the Arterial Wall“. Physiology 14, Nr. 2 (April 1999): 68–73. http://dx.doi.org/10.1152/physiologyonline.1999.14.2.68.
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The main task of the arterial system is to secure an adequate supply of oxygen to organs. This fact implies the integration of multiple signals in the vascular wall. This review deals with the exchange of information between and among smooth muscle and endothelial cells through gap junctions in the vessel walls of arteries and arterioles.
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Saha, S., J. C. Klewicki, A. Ooi und H. M. Blackburn. „On scaling pipe flows with sinusoidal transversely corrugated walls: analysis of data from the laminar to the low-Reynolds-number turbulent regime“. Journal of Fluid Mechanics 779 (14.08.2015): 245–74. http://dx.doi.org/10.1017/jfm.2015.414.
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Direct numerical simulation was used to study laminar and turbulent flows in circular pipes with smoothly corrugated walls. The corrugation wavelength was kept constant at $0.419D$, where $D$ is the mean diameter of the wavy-wall pipe and the corrugation height was varied from zero to $0.08D$. Flow rates were varied in steps between low values that generate laminar flow and higher values where the flow is in the post-transitional turbulent regime. Simulations in the turbulent regime were also carried out at a constant Reynolds number, $\mathit{Re}_{{\it\tau}}=314$, for all corrugation heights. It was found that even in the laminar regime, larger-amplitude corrugations produce flow separation. This leads to the proportion of pressure drop attributable to pressure drag being approximately 50 %, and rising to approximately 85 % in transitional rough-wall flow. The near-wall structure of turbulent flow is seen to be heavily influenced by the effects of flow separation and reattachment. Farther from the wall, the statistical profiles examined exhibit behaviours characteristic of smooth-wall flows or distributed roughness rough-wall flows. These observations support Townsend’s wall-similarity hypothesis. The organized nature of the present roughness allows the mean pressure drop to be written as a function of the corrugation height. When this is exploited in an analysis of the mean dynamical equation, the scaling problem is explicitly revealed to result from the combined influences of roughness and Reynolds number. The present results support the recent analysis and observations of Mehdi et al. (J. Fluid Mech., vol. 731, 2013, pp. 682–712), indicating that the length scale given by the distance from the wall at which the mean viscous force loses leading order is important to describing these combined influences, as well as providing a dynamically self-consistent connection to the scaling structure of smooth-wall pipe flow.
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Rau, G., M. C¸akan, D. Moeller und T. Arts. „The Effect of Periodic Ribs on the Local Aerodynamic and Heat Transfer Performance of a Straight Cooling Channel“. Journal of Turbomachinery 120, Nr. 2 (01.04.1998): 368–75. http://dx.doi.org/10.1115/1.2841415.
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The local aerodynamic and heat transfer performance were measured in a rib-roughened square duct as a function of the rib pitch to height ratio. The blockage ratio of these square obstacles was 10 or 20 percent depending on whether they were placed on one single (1s) or on two opposite walls (2s). The Reynolds number, based on the channel mean velocity and hydraulic diameter, was fixed at 30,000. The aerodynamic description of the flow field was based on local pressure distributions along the ribbed and adjacent smooth walls as well as on two-dimensional LDV explorations in the channel symmetry plane and in two planes parallel to the ribbed wall(s). Local heat transfer distributions were obtained on the floor, between the ribs, and on the adjacent smooth side wall. Averaged parameters, such as friction factor and averaged heat transfer enhancement factor, were calculated from the local results and compared to correlations given in literature. This contribution showed that simple correlations derived from the law of the wall similarity and from the Reynolds analogy could not be applied for the present rib height-to-channel hydraulic diameter ratio (e/Dh = 0.1). The strong secondary flows resulted in a three-dimensional flow field with high gradients in the local heat transfer distributions on the smooth side walls.
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Saito, Namiko, Dale I. Pullin und Michio Inoue. „Large eddy simulation of smooth-wall, transitional and fully rough-wall channel flow“. Physics of Fluids 24, Nr. 7 (Juli 2012): 075103. http://dx.doi.org/10.1063/1.4731301.
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Xu, Yuncheng, und Xiaofeng Liu. „An immersed boundary method with y + ‐adaptive wall function for smooth wall shear“. International Journal for Numerical Methods in Fluids 93, Nr. 6 (02.02.2021): 1929–46. http://dx.doi.org/10.1002/fld.4960.
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Van Doorslaer, Koen, und Julien De Rouck. „REDUCTION ON WAVE OVERTOPPING ON A SMOOTH DIKE BY MEANS OF A PARAPET“. Coastal Engineering Proceedings 1, Nr. 32 (26.01.2011): 6. http://dx.doi.org/10.9753/icce.v32.structures.6.
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A return wall or parapet is a very efficient construction built to reduce wave overtopping over sea structures. One of its main advantages is that this relative small construction can be built in a dike without increasing the crest height yet creating a major reduction in wave overtopping. In this paper only non-breaking waves attacking smooth dikes are investigated. A normal smooth dike, a smooth dike with vertical wall and a smooth dike with parapet have been tested. The results lead to reduction factors for a vertical wall or a parapet that can be introduced in the van der Meer formulas for wave overtopping over smooth dikes. The optimal geometry of the parapet has been subject of the research as well.
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SCHULTZ, M. P., und K. A. FLACK. „The rough-wall turbulent boundary layer from the hydraulically smooth to the fully rough regime“. Journal of Fluid Mechanics 580 (21.05.2007): 381–405. http://dx.doi.org/10.1017/s0022112007005502.
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Turbulence measurements for rough-wall boundary layers are presented and compared to those for a smooth wall. The rough-wall experiments were made on a three-dimensional rough surface geometrically similar to the honed pipe roughness used by Shockling, Allen & Smits (J. Fluid Mech. vol. 564, 2006, p. 267). The present work covers a wide Reynolds-number range (Reθ = 2180–27 100), spanning the hydraulically smooth to the fully rough flow regimes for a single surface, while maintaining a roughness height that is a small fraction of the boundary-layer thickness. In this investigation, the root-mean-square roughness height was at least three orders of magnitude smaller than the boundary-layer thickness, and the Kármán number (δ+), typifying the ratio of the largest to the smallest turbulent scales in the flow, was as high as 10100. The mean velocity profiles for the rough and smooth walls show remarkable similarity in the outer layer using velocity-defect scaling. The Reynolds stresses and higher-order turbulence statistics also show excellent agreement in the outer layer. The results lend strong support to the concept of outer layer similarity for rough walls in which there is a large separation between the roughness length scale and the largest turbulence scales in the flow.
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Shibata, Masahiro, Kairong Qin, Shigeru Ichioka und Akira Kamiya. „Vascular wall energetics in arterioles during nitric oxide-dependent and -independent vasodilation“. Journal of Applied Physiology 100, Nr. 6 (Juni 2006): 1793–98. http://dx.doi.org/10.1152/japplphysiol.01632.2005.
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The objective of this study was to evaluate whether the nitric oxide (NO) released from vascular endothelial cells would decrease vessel wall oxygen consumption by decreasing the energy expenditure of mechanical work by vascular smooth muscle. The oxygen consumption rate of arteriolar walls in rat cremaster muscle was determined in vivo during NO-dependent and -independent vasodilation on the basis of the intra- and perivascular oxygen tension (Po2) measured by phosphorescence quenching laser microscopy. NO-dependent vasodilation was induced by increased NO production due to increased blood flow, whereas NO-independent vasodilation was induced by topical administration of papaverine. The energy efficiency of vessel walls was evaluated by the variable ratio of circumferential wall stress (amount of mechanical work) to vessel wall oxygen consumption rate (energy cost) in the arteriole between normal and vasodilated conditions. NO-dependent and -independent dilation increased arteriolar diameters by 13 and 17%, respectively, relative to the values under normal condition. Vessel wall oxygen consumption decreased significantly during both NO-dependent and -independent vasodilation compared with that under normal condition. However, vessel wall oxygen consumption during NO-independent vasodilation was significantly lower than that during NO-dependent vasodilation. On the other hand, there was no significant difference between the energy efficiency of vessel walls during NO-dependent and -independent vasodilation, suggesting the decrease in vessel wall oxygen consumption produced by NO to be related to reduced mechanical work of vascular smooth muscle.
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Fredericks, R. K., S. Raju und M. Klein. „Ultrastructure of Evolving Deep Venous Collaterals“. Phlebology: The Journal of Venous Disease 12, Nr. 2 (Juni 1997): 60–63. http://dx.doi.org/10.1177/026835559701200204.
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Objective: To explore the structure of obstructive venous collaterals. Design: A total of 25 rats underwent unilateral ligation of the distal common femoral vein. Bilateral (control and test) vein segments with collaterals were harvested and studied with conventional light microscopy and electron microscopy at 2-week intervals for 10 weeks post-ligation. Results: Obstructive collaterals were quite unlike normal controls throughout the study. Initially, post-obstructive collateral walls showed disorganization of collagen, elastin, smooth muscle cells, and adventitia, while endothelial cells became more rounded and compact. The dense protein subendothelial deposits noted early became organized and moved more deeply into the wall at subsequent study intervals. Minimal motivation of smooth muscle cells, coalescence of elastic lamina, condensation of collagen and some organization of the wall were noted. Conclusion: Inability of deep collaterals to function with normal wall properties is likely to be secondary to the disruption of connective tissue and sustained disorganization of the vein wall noted throughout the evolution of collateral formation.
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Ramchandani, R., X. Shen, C. L. Elmsley, W. T. Ambrosius, S. J. Gunst und R. S. Tepper. „Differences in airway structure in immature and mature rabbits“. Journal of Applied Physiology 89, Nr. 4 (01.10.2000): 1310–16. http://dx.doi.org/10.1152/jappl.2000.89.4.1310.
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Our laboratory has previously demonstrated that maximal bronchoconstriction produces a greater degree of airway narrowing in immature than in mature rabbit lungs (33). To determine whether these maturational differences could be related to airway structure, we compared the fraction of the airway wall occupied by airway smooth muscle (ASM) and cartilage, the proportion of wall area internal to ASM, and the number of alveolar attachments to the airways, from mature and immature (6-mo- and 4-wk-old, respectively) rabbit lungs that were formalin fixed at total lung capacity. The results demonstrate that the airway walls of immature rabbits had a greater percentage of smooth muscle, a lower percentage of cartilage, and fewer alveolar attachments compared with mature rabbit airways; however, we did not find maturational differences in the airway wall thickness relative to airway size. We conclude that structural differences in the airway wall may contribute to the greater airway narrowing observed in immature rabbits during bronchoconstriction.
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Hasson, D. A., und W. L. Flint. „An Investigation of the Liquid Petrol Wall Film in the Manifold of a Carburetted Spark Ignition Engine: Effect of Carburettor and Manifold Geometry on Wall Film Quantities, Engine Performance and Emissions“. Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 203, Nr. 2 (April 1989): 77–89. http://dx.doi.org/10.1243/pime_proc_1989_203_153_02.
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The rate of deposition on the manifold wall of liquid droplets from the multi-component, two-phase stream of fluid flowing in the inlet manifold of a carburetted petrol engine and the re-entrainment of droplets into the stream from the liquid film which flows on the walls have been investigated using a single cylinder crossflow engine. The effect of throttle opening, straight manifold length, a smooth bend and a mitre bend is reported: measurements of exhaust emissions and cycle-to-cycle pressure variation of cylinder pressure are related to wall film quantities. It was found that throttle position was important in determining the initial wall film, that the average thickness of the film decreases with length along the straight manifold and that droplet re-entrainment from a sharp bend is greater than from a smooth bend. Removal of the wall film yields a significant reduction in the emission of unburned hydrocarbons and virtually eliminates cycle-to-cycle variations of pressure in the engine cylinder.
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Salameh, Tareq, und Bengt Sunden. „A numerical investigation of heat transfer in a smooth bend part of a U-duct“. International Journal of Numerical Methods for Heat & Fluid Flow 24, Nr. 1 (20.12.2013): 137–47. http://dx.doi.org/10.1108/hff-03-2012-0066.
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Purpose – The aim of this paper is to study two-dimensional numerical simulations of the flow and temperature fields inside the bend (turn) part of a U-duct. Design/methodology/approach – Several turbulence models based on two and five equations were used to solve the momentum and energy equations inside the bend (turn) part of the U-duct. For two-equation models, both the renormalization group and realizable k-ɛ turbulence models were implemented. The five-equation model used is a Reynolds stress model with different wall boundary conditions. Standard, non-equilibrium and enhanced wall functions were used in parallel with the two- and five-equation models to treat the turbulent flow near the duct walls. Findings – Several turbulence models were used to simulate the flow and temperature fields along the bend part of a U-duct with different inlet and thermal boundary conditions. The numerical results indicate that the renormalization and realizable k-ɛ turbulence models with standard wall function treatment gave the best results when compared with experimental data obtained for similar conditions. Research limitations/implications – For heat transfer analysis, two different thermal boundary conditions, i.e. constant wall temperature and constant heat flux at the wall are implemented. The results are calculated for Reynolds number equal 20,000. Practical implications – The results can be used in designing heat exchangers, piping and duct systems, and internal passage cooling of gas turbine blades. Originality/value – The numerical results obtained here concentrate on the detailed investigation of flow and temperature field at the outer wall of the bend part. Different boundary conditions at the inlet and the outer bend walls of the U-duct were applied to study how these boundary conditions affect the flow and temperature fields.
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Dunford, Joseph R., E. Josiah Lutton, Jolene Atia, Andrew M. Blanks und Hugo A. van den Berg. „Computational physiology of uterine smooth muscle“. Science Progress 102, Nr. 2 (20.05.2019): 103–26. http://dx.doi.org/10.1177/0036850419850431.
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Pregnancy can be accompanied by serious health risks to mother and child, such as pre-eclampsia, premature birth and postpartum haemorrhage. Understanding of the normal physiology of uterine function is essential to an improved management of such risks. Here we focus on the physiology of the smooth muscle fibres which make up the bulk of the uterine wall and which generate the forceful contractions that accompany parturition. We survey computational methods that integrate mathematical modelling with data analysis and thereby aid the discovery of new therapeutic targets that, according to clinical needs, can be manipulated to either stop contractions or cause the uterine wall muscle to become active.
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Shevchenko, Marina A., Andrey O. Bogorodskiy, Natalia I. Troyanova, Ekaterina A. Servuli, Elena L. Bolkhovitina, Georg Büldt, Christoph Fahlke et al. „Aspergillus fumigatusInfection-Induced Neutrophil Recruitment and Location in the Conducting Airway of Immunocompetent, Neutropenic, and Immunosuppressed Mice“. Journal of Immunology Research 2018 (2018): 1–12. http://dx.doi.org/10.1155/2018/5379085.
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Susceptibility to fungal infection is commonly associated with impaired neutrophil responses. To study the mechanisms underlying this association, we investigated neutrophil recruitment to the conducting airway wall afterAspergillus fumigatusconidium inhalation in mouse models of drug-induced immunosuppression and antibody-mediated neutrophil depletion (neutropenia) by performing three-dimensional confocal laser-scanning microscopy of whole-mount primary bronchus specimens. Actin staining enabled visualization of the epithelial and smooth muscle layers that mark the airway wall. Gr-1+or Ly6G+neutrophils located between the epithelium and smooth muscles were considered airway wall neutrophils. The number of airway wall neutrophils for immunocompetent, immunosuppressed, and neutropenic mice before and 6 h afterA. fumigatusinfection were analyzed and compared. Our results show that the number of conducting airway wall neutrophils in immunocompetent mice significantly increased upon inflammation, while a dramatic reduction in this number was observed following immunosuppression and neutropenia. Interestingly, a slight increase in the infiltration of neutrophils into the airway wall was detected as a result of infection, even in immunosuppressed and neutropenic mice. Taken together, these data indicate that neutrophils are present in intact conducting airway walls and the number elevates uponA. fumigatusinfection. Conducting airway wall neutrophils are affected by both neutropenia and immunosuppression.
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Verschoof, Ruben A., Dennis Bakhuis, Pim A. Bullee, Sander G. Huisman, Chao Sun und Detlef Lohse. „The influence of wall roughness on bubble drag reduction in Taylor–Couette turbulence“. Journal of Fluid Mechanics 851 (20.07.2018): 436–46. http://dx.doi.org/10.1017/jfm.2018.515.
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We experimentally study the influence of wall roughness on bubble drag reduction in turbulent Taylor–Couette flow, i.e. the flow between two concentric, independently rotating cylinders. We measure the drag in the system for the cases with and without air, and add roughness by installing transverse ribs on either one or both of the cylinders. For the smooth-wall case (no ribs) and the case of ribs on the inner cylinder only, we observe strong drag reduction up to DR$=33\,\%$ and DR$=23\,\%$, respectively, for a void fraction of $\unicode[STIX]{x1D6FC}=6\,\%$. However, with ribs mounted on both cylinders or on the outer cylinder only, the drag reduction is weak, less than DR$=11\,\%$, and thus quite close to the trivial effect of reduced effective density. Flow visualizations show that stable turbulent Taylor vortices – large-scale vortical structures – are induced in these two cases, i.e. the cases with ribs on the outer cylinder. These strong secondary flows move the bubbles away from the boundary layer, making the bubbles less effective than what had previously been observed for the smooth-wall case. Measurements with counter-rotating smooth cylinders, a regime in which pronounced Taylor rolls are also induced, confirm that it is really the Taylor vortices that weaken the bubble drag reduction mechanism. Our findings show that, although bubble drag reduction can indeed be effective for smooth walls, its effect can be spoiled by e.g. biofouling and omnipresent wall roughness, as the roughness can induce strong secondary flows.
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Gre´goire, G., M. Favre-Marinet und F. Julien Saint Amand. „Modeling of Turbulent Fluid Flow Over a Rough Wall With or Without Suction“. Journal of Fluids Engineering 125, Nr. 4 (01.07.2003): 636–42. http://dx.doi.org/10.1115/1.1593705.
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The turbulent flow close to a wall with two-dimensional roughness is computed with a two-layer zonal model. For an impermeable wall, the classical logarithmic law compares well with the numerical results if the location of the fictitious wall modeling the surface is considered at the top of the rough boundary. The model developed by Wilcox for smooth walls is modified to account for the surface roughness and gives satisfactory results, especially for the friction coefficient, for the case of boundary layer suction.
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Han, J. C., Y. M. Zhang und Kathrin Kalkuehler. „Uneven Wall Temperature Effect on Local Heat Transfer in a Rotating Two-Pass Square Channel With Smooth Walls“. Journal of Heat Transfer 115, Nr. 4 (01.11.1993): 912–20. http://dx.doi.org/10.1115/1.2911387.
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The influence of uneven wall temperature on the local heat transfer coefficient in a rotating, two-pass, square channel with smooth walls is investigated for rotation numbers from 0.0352 to 0.352 by varying Reynolds numbers from 25,000 to 2500. The two-pass square channel, composed of 12 isolated copper sections, has a length-to-hydraulic diameter ratio of 12. The mean rotating radius to the channel hydraulic diameter ratio is kept at a constant value of 30. Three cases of thermal boundary conditions are studied: (A) four walls at the same temperature, (B) four walls at the same heat flux, and (C) trailing wall hotter than leading with side walls unheated and insulated. The results for case A of four walls at the same temperature show that the first channel (radial outward flow) heat transfer coefficients on the leading surface are much lower than that of the trailing surface due to the combined effect of Coriolis and buoyancy forces. The second channel (radial inward flow) heat transfer coefficients on the leading surface are higher than that of the trailing surface. The difference between the heat transfer coefficients for the leading and trailing surface in the second channel is smaller than that in the first channel due to the opposite effect of Coriolis and buoyancy forces in the second channel. However, the heat transfer coefficients on each wall in each channel for cases B and C are higher than case A because of interactions between rotation-induced secondary flows and uneven wall temperatures in cases B and C. The results suggest that the effect of uneven wall temperatures on local heat transfer coefficients in the second channel is greater than that in the first channel.
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Moon, H. K., T. O’Connell und R. Sharma. „Heat Transfer Enhancement Using a Convex-Patterned Surface“. Journal of Turbomachinery 125, Nr. 2 (01.04.2003): 274–80. http://dx.doi.org/10.1115/1.1556404.
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The heat transfer rate from a smooth wall in an internal cooling passage can be significantly enhanced by using a convex patterned surface on the opposite wall of the passage. This design is particularly effective for a design that requires the heat transfer surface to be free of any augmenting features (smooth). Heat transfer coefficients on the smooth wall in a rectangular channel, which had convexities on the opposite wall were experimentally investigated. Friction factors were also measured to assess the thermal performance. Relative clearances δ/d between the convexities and the smooth wall of 0, 0.024, and 0.055 were investigated in a Reynolds number ReHD range from 15,000 to 35,000. The heat transfer coefficients were measured in the thermally developed region using a transient thermochromic liquid crystal technique. The clearance gap between the convexities and the smooth wall adversely affected the heat transfer enhancement NuHD. The friction factors (f ), measured in the aerodynamically developed region, were largest for the cases of no clearance δ/d=0). The average heat transfer enhancement Nu¯HD was also largest for the cases of no clearance δ/d=0, as high as 3.08 times at a Reynolds number of 11,456 in relative to that Nuo of an entirely smooth channel. The normalized Nusselt numbers Nu¯HD/Nuo, as well as the normalized friction factors f/fo, for all three cases, decreased with Reynolds numbers. However, the decay rate of the friction factor ratios f/fo with Reynolds numbers was lower than that of the normalized Nusselt numbers. For all three cases investigated, the thermal performance Nu¯HD/Nuo/f/fo1/3 values were within 5% to each other. The heat transfer enhancement using a convex patterned surface was thermally more effective at a relative low Reynolds numbers (less than 20,000 for δ/d=0) than that of a smooth channel.
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Moreno-Martínez, Ana Esther, Emilia Gómez-Molero, Pablo Sánchez-Virosta, Henk L. Dekker, Albert de Boer, Elena Eraso, Oliver Bader und Piet W. J. de Groot. „High Biofilm Formation of Non-Smooth Candida parapsilosis Correlates with Increased Incorporation of GPI-Modified Wall Adhesins“. Pathogens 10, Nr. 4 (19.04.2021): 493. http://dx.doi.org/10.3390/pathogens10040493.
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Candida parapsilosis is among the most frequent causes of candidiasis. Clinical isolates of this species show large variations in colony morphotype, ranging from round and smooth to a variety of non-smooth irregular colony shapes. A non-smooth appearance is related to increased formation of pseudohyphae, higher capacity to form biofilms on abiotic surfaces, and invading agar. Here, we present a comprehensive study of the cell wall proteome of C. parapsilosis reference strain CDC317 and seven clinical isolates under planktonic and sessile conditions. This analysis resulted in the identification of 40 wall proteins, most of them homologs of known Candida albicans cell wall proteins, such as Gas, Crh, Bgl2, Cht2, Ecm33, Sap, Sod, Plb, Pir, Pga30, Pga59, and adhesin family members. Comparative analysis of exponentially growing and stationary phase planktonic cultures of CDC317 at 30 °C and 37 °C revealed only minor variations. However, comparison of smooth isolates to non-smooth isolates with high biofilm formation capacity showed an increase in abundance and diversity of putative wall adhesins from Als, Iff/Hyr, and Hwp families in the latter. This difference depended more strongly on strain phenotype than on the growth conditions, as it was observed in planktonic as well as biofilm cells. Thus, in the set of isolates analyzed, the high biofilm formation capacity of non-smooth C. parapsilosis isolates with elongated cellular phenotypes correlates with the increased surface expression of putative wall adhesins in accordance with their proposed cellular function.
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Ismail, Umair, Tamer A. Zaki und Paul A. Durbin. „Simulations of rib-roughened rough-to-smooth turbulent channel flows“. Journal of Fluid Mechanics 843 (21.03.2018): 419–49. http://dx.doi.org/10.1017/jfm.2018.119.
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High-fidelity simulations of turbulent flow through a channel with a rough wall, followed by a smooth wall, demonstrate a high degree of non-equilibrium within the recovery region. In fact, the recovery of all the flow statistics studied is incomplete by the streamwise exit of the computational domain. Above a thin wall layer, turbulence intensities significantly higher than fully developed, smooth-wall levels persist in the developing region. Within the thin wall layer, the profile shapes for turbulence stresses recover very quickly and wall-normal locations of characteristic peaks are established. However, even in this thin layer, complete recovery of magnitudes of turbulence stresses is exceptionally slow. A similar initially swift but eventually incomplete and slow relaxation behaviour is also shown by the skin friction. Between the turbulence shear and streamwise stresses, the turbulence shear stress shows a comparatively quick rate of recovery above a thin wall layer. Over the developing smooth wall, the balance is not merely between fluxes due to pressure and shear stresses. Strong momentum fluxes, which are directly influenced by the upstream roughness size, contribute significantly to this balance. Approximate curve fits estimate the streamwise distance required by the outer peaks of Reynolds stresses to attain near-fully-developed levels at approximately $20\unicode[STIX]{x1D6FF}{-}25\unicode[STIX]{x1D6FF}$, with $\unicode[STIX]{x1D6FF}$ being the channel half height. An even longer distance, of more than $50\unicode[STIX]{x1D6FF}$, might be needed by the mean velocity to approach near-fully-developed magnitudes. Visualizations and correlations show that large-scale eddies that are created above the roughness persist downstream, and sporadically perturb the elongated streaks. These streaks of alternating high and low momentum appear almost instantly after the roughness is removed. The mean flow does not re-establish an equilibrium log layer within the computational domain, and the velocity deficit created by the roughness continues throughout the domain. On the step change in roughness, near the wall, profiles for turbulence kinetic energy dissipation rate, $\unicode[STIX]{x1D716}$, and energy spectra indicate a sharp reduction in energy at small scales. Despite this, reversion towards equilibrium smooth-wall levels is slow, and ultimately incomplete, due to a rather slow adjustment of the turbulence cascade. The non-dimensional roughness height, $k^{+}$ ranges from 42 to 254 and the friction velocity Reynolds number at the smooth wall, $Re_{\unicode[STIX]{x1D70F}S}$, ranges from 284 to 1160 in the various simulations.
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Sparrow, E. M., und D. R. Otis. „Ductflow heat transfer at a smooth wall which faces a wall covered by protuberances“. International Journal of Heat and Mass Transfer 28, Nr. 7 (Juli 1985): 1317–26. http://dx.doi.org/10.1016/0017-9310(85)90162-0.
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