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Journal articles on the topic "Axial peak suppression"
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Toraya, H., and T. Ochiai. "Refinement of unit-cell parameters by whole-powder-pattern fitting technique." Powder Diffraction 9, no. 4 (December 1994): 272–79. http://dx.doi.org/10.1017/s0885715600018996.
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The accuracy of the unit-cell parameters refined by using the whole-powder-pattern decomposition method is discussed. Powders of W, ZnO, TiO2, BaTiO3 Mg2SiO4, Al2SiO5 (+α-SiO2), and monoclinic ZrO2 were used as test samples. Two internal standard reference materials of Si and CeO2 and two types of powder diffractometers were used for data collections. The systematic peak-shift was corrected by determining the unit-cell parameters and the error function simultaneously during the whole-pattern-fitting. The estimated standard deviations for sample means ranged from <10 ppm (10−6) in cubic symmetry to 20∼50 ppm in monoclinic symmetry. These analyses could be carried out almost automatically in a computation time of less than l min for each sample on a workstation. The use of symmetric experimental profiles, obtained by the suppression of axial divergence, is very effective and of essential importance for improving the accuracy of unit-cell parameters.
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Wang, Weijun, and Zhenggui Li. "Influence of different types of volutes on centrifugal aviation fuel pump." Advances in Mechanical Engineering 13, no. 3 (March 2021): 168781402110052. http://dx.doi.org/10.1177/16878140211005202.
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High efficiency and low vibration are two hot topics in the field of fluid mechanics. In this paper, different spiral volutes are designed for centrifugal aviation fuel pump based on Velocity Coefficient Method. Physical fields under different operating conditions are simulated by computational fluid dynamics (CFD) software that solved the Navier–Stokes equations for three-dimensional flow (3D-RANS). And theoretical and simulation values of radial and axial forces are analyzed. The unsteady pressure fluctuation based on the steady results at the monitoring point is solved and Fast Fourier Transform (FFT) is used to obtain the influence of different volutes on pressure pulsation. The influence of three volutes on is analyzed and compared with the simulation. The results show that the double volutes improve significantly the large flow efficiency of the aviation fuel pump, 20%–30% higher than that of the single volute. The doubles volute can also optimize the radial force under the off-design condition. The radial force of the single volute fuel pump is 100 N. The radial force of the two types of double volute fuel pump is between 10 and 20 N. The three types of volute have no obvious influence on the axial force. Two types of double volutes provide excellent suppression of fuel pump pulsation spikes over the full frequency range. The peak value of single volute is mainly concentrated in the low frequency area below 2000 Hz. The blade frequency (170 Hz) and frequency multiplication are the main frequencies of the pulsation and the pulsation decreases rapidly in the high frequency area. The research results provide theoretical support for the design of aviation fuel pump with low pressure pulsation.
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Farag, Ashraf, Jeffery Hammersley, Dan Olson, and Terry Ng. "Mechanics of the Flow in the Small and Middle Human Airways." Journal of Fluids Engineering 122, no. 3 (May 3, 2000): 576–84. http://dx.doi.org/10.1115/1.1287724.
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Steady divergent flow (inspiration directed) is measured using Laser Doppler Velocimetry in a large-scale model carefully mimicing the morphometry of small human airways. The anatomical features, which induced vorticity in the flow from vorticity free entrance flow, are evaluated under conditions of convective similitude. The flow pattern in the daughter tubes is typical of laminar flow within the entrance to sharp bends (Dean number >500) with rapid development of strong secondary flows (maximum secondary velocity is 45 percent of mean axial velocity). The secondary flow consists of two main vortices, with two smaller and weaker secondary vortex activities toward the inner wall of curvature. There appears to be time dependent interaction with these vortices causing warbling at specific flow conditions. The calculated vorticity transport along the flow axis showed interaction between the viscous force at the new boundary layer development along the carinal wall and centrifugal force of curvature, with a significant influence by the upstream flow prior to entering the actual flow division. This interplay results in an overshoot of the calculated vorticity transport comparable to flow entering curved bends and suppression for the tendency to separate at the inner wall of these tight bends. The maximum primary flow velocities are skewed toward the carinal side (outer wall of curvature) and development of a second peak occurred with convection of the high velocity elements toward the inner wall of curvature by the strong secondary flow. [S0098-2202(00)01903-9]
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Wong, K. W. L., J. Zhao, D. Lo Jacono, M. C. Thompson, and J. Sheridan. "Experimental investigation of flow-induced vibration of a sinusoidally rotating circular cylinder." Journal of Fluid Mechanics 848 (June 5, 2018): 430–66. http://dx.doi.org/10.1017/jfm.2018.379.
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The present experimental investigation characterises the dynamic response and wake structure of a sinusoidally rotating circular cylinder with a low mass ratio (defined as the ratio of the total oscillating mass to the displaced fluid mass) undergoing cross-stream flow-induced vibration (FIV). The study covers a wide parameter space spanning the forcing rotary oscillation frequency ratio $0\leqslant f_{r}^{\ast }\leqslant 4.5$ and the forcing rotation speed ratio $0\leqslant \unicode[STIX]{x1D6FC}_{r}^{\ast }\leqslant 2.0$, at reduced velocities associated with the vortex-induced vibration (VIV) upper and lower amplitude response branches. Here, $f_{r}^{\ast }=f_{r}/f_{nw}$ and $\unicode[STIX]{x1D6FC}_{r}^{\ast }=\unicode[STIX]{x1D6FA}_{o}D/(2U)$, where $f_{r}$ is the forcing rotary oscillation frequency, $f_{nw}$ is the natural frequency of the system in quiescent fluid (water), $\unicode[STIX]{x1D6FA}_{o}$ is the peak angular rotation speed, $D$ is the cylinder diameter and $U$ is the free-stream velocity; the reduced velocity is defined by $U^{\ast }=U/(\,f_{nw}D)$. The fluid–structure system was modelled using a low-friction air-bearing system in conjunction with a free-surface recirculating water channel, with axial rotary motion provided by a microstepping motor. The cylinder was allowed to vibrate with only one degree of freedom transverse to the oncoming free-stream flow. It was found that in specific ranges of $f_{r}^{\ast }$, the body vibration frequency may deviate from that seen in the non-rotating case and lock onto the forcing rotary oscillation frequency or its one-third subharmonic. The former is referred to as the ‘rotary lock-on’ (RLO) region and the latter as the ‘tertiary lock-on’ (TLO) region. Significant increases in the vibration amplitude and suppression of VIV could both be observed in different parts of the RLO and TLO regions. The peak amplitude response in the case of $U^{\ast }=5.5$ (upper branch) was observed to be $1.2D$, an increase of approximately $50\,\%$ over the non-rotating case, while in the case of $U^{\ast }=8.0$ (lower branch), the peak amplitude response was $2.2D$, a remarkable increase of $270\,\%$ over the non-rotating case. Notably, the results showed that the amplitude responses at moderate Reynolds numbers ($Re=UD/\unicode[STIX]{x1D708}=2060$ and $2940$, where $\unicode[STIX]{x1D708}$ is the kinematic viscosity of the fluid) in the present study showed significant differences from those of a previous low-Reynolds-number ($Re=350$) numerical study at similar reduced velocities by Du & Sun (Phys. Fluids, vol. 14 (8), 2015, pp. 2767–2777). Remarkably, in an additional study examining the cylinder vibration as a function of $U^{\ast }$ while the fixed forcing rotary oscillation parameters were kept constant at $(f_{r}^{\ast },\unicode[STIX]{x1D6FC}_{r}^{\ast })=(1.0,1.0)$, the cylinder experienced substantially larger oscillations than in the non-rotating case, and a rotation-induced galloping response was observed for $U^{\ast }>12$, where the amplitude increased monotonically to reach approximately $3.0D$ at the highest reduced velocity ($U^{\ast }=20$) tested. Furthermore, new wake modes were identified in the RLO and TLO regions using particle image velocimetry measurements at selected points in the $f_{r}^{\ast }-\unicode[STIX]{x1D6FC}_{r}^{\ast }$ parameter space.
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Sareen, A., J. Zhao, D. Lo Jacono, J. Sheridan, K. Hourigan, and M. C. Thompson. "Vortex-induced vibration of a rotating sphere." Journal of Fluid Mechanics 837 (December 20, 2017): 258–92. http://dx.doi.org/10.1017/jfm.2017.847.
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Vortex-induced vibration (VIV) of a sphere represents one of the most generic fundamental fluid–structure interaction problems. Since vortex-induced vibration can lead to structural failure, numerous studies have focused on understanding the underlying principles of VIV and its suppression. This paper reports on an experimental investigation of the effect of imposed axial rotation on the dynamics of vortex-induced vibration of a sphere that is free to oscillate in the cross-flow direction, by employing simultaneous displacement and force measurements. The VIV response was investigated over a wide range of reduced velocities (i.e. velocity normalised by the natural frequency of the system): $3\leqslant U^{\ast }\leqslant 18$, corresponding to a Reynolds number range of $5000<Re<30\,000$, while the rotation ratio, defined as the ratio between the sphere surface and inflow speeds, $\unicode[STIX]{x1D6FC}=|\unicode[STIX]{x1D714}|D/(2U)$, was varied in increments over the range of $0\leqslant \unicode[STIX]{x1D6FC}\leqslant 7.5$. It is found that the vibration amplitude exhibits a typical inverted bell-shaped variation with reduced velocity, similar to the classic VIV response for a non-rotating sphere but without the higher reduced velocity response tail. The vibration amplitude decreases monotonically and gradually as the imposed transverse rotation rate is increased up to $\unicode[STIX]{x1D6FC}=6$, beyond which the body vibration is significantly reduced. The synchronisation regime, defined as the reduced velocity range where large vibrations close to the natural frequency are observed, also becomes narrower as $\unicode[STIX]{x1D6FC}$ is increased, with the peak saturation amplitude observed at progressively lower reduced velocities. In addition, for small rotation rates, the peak amplitude decreases almost linearly with $\unicode[STIX]{x1D6FC}$. The imposed rotation not only reduces vibration amplitudes, but also makes the body vibrations less periodic. The frequency spectra revealed the occurrence of a broadband spectrum with an increase in the imposed rotation rate. Recurrence analysis of the structural vibration response demonstrated a transition from periodic to chaotic in a modified recurrence map complementing the appearance of broadband spectra at the onset of bifurcation. Despite considerable changes in flow structure, the vortex phase ($\unicode[STIX]{x1D719}_{vortex}$), defined as the phase between the vortex force and the body displacement, follows the same pattern as for the non-rotating case, with the $\unicode[STIX]{x1D719}_{vortex}$ increasing gradually from low values in Mode I of the sphere vibration to almost $180^{\circ }$ as the system undergoes a continuous transition to Mode II of the sphere vibration at higher reduced velocity. The total phase ($\unicode[STIX]{x1D719}_{total}$), defined as the phase between the transverse lift force and the body displacement, only increases from low values after the peak amplitude response in Mode II has been reached. It reaches its maximum value (${\sim}165^{\circ }$) close to the transition from the Mode II upper plateau to the lower plateau, reminiscent of the behaviour seen for the upper to lower branch transition for cylinder VIV. Hydrogen-bubble visualisations and particle image velocimetry (PIV) performed in the equatorial plane provided further insights into the flow dynamics near the sphere surface. The mean wake is found to be deflected towards the advancing side of the sphere, associated with an increase in the Magnus force. For higher rotation ratios, the near-wake rear recirculation zone is absent and the flow is highly vectored from the retreating side to the advancing side, giving rise to large-scale shedding. For a very high rotation ratio of $\unicode[STIX]{x1D6FC}=6$, for which vibrations are found to be suppressed, a one-sided large-scale shedding pattern is observed, similar to the shear-layer instability one-sided shedding observed previously for a rigidly mounted rotating sphere.
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Huang, Xiuchang, Zhiwei Su, Sen Wang, Xinsheng Wei, Yong Wang, and Hongxing Hua. "High-frequency disturbance force suppression mechanism of a flywheel equipped with a flexible dynamic vibration absorber." Journal of Vibration and Control 26, no. 23-24 (March 16, 2020): 2113–24. http://dx.doi.org/10.1177/1077546320915340.
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Flywheels generate speed-related disturbances and induce micro-vibrations that influence the performance of high-sensitivity instruments on board. This study addresses dynamic modeling and disturbance force suppression of the flywheels due to its inherent characteristic structural modes. The disturbance force transmission of a rotating flywheel due to a unit radial force applied at the rim of the wheel body is reported using the three-dimensional finite element method and frequency response function–based substructuring method. The characteristic structural modes for the radial and axial disturbance forces are identified. The axial deformation–dominated flapping mode and the radial deformation–dominated transverse mode will contribute most to the axial and radial disturbance forces, respectively. A flexible ring structure, which is rested on the arms of the wheel body through independent viscoelastic pads and simultaneously in contact with the inner rim of the wheel body by independent resilient cushion members, is proposed to function as a damped dynamic vibration absorber. The modes of the dynamic vibration absorber and the modes of the flywheel equipped with the dynamic vibration absorber are analyzed. It is shown that the dynamic vibration absorber is effective to suppress both the radial and axial disturbance forces at the characteristic structural modes under different rotational speeds, provided that the loss factor of the complex elastic modulus for the viscoelastic pads is larger than 0.2 and the proportional damping constant for the stiffness matrix is larger than 6 Ns/m. Experimental analyses are conducted on a flywheel with a well-designed dynamic vibration absorber to validate the theoretical findings. Modal tests and disturbance force measurements are carried out for the flywheel with/without the dynamic vibration absorber. It is shown that the identified characteristic structural modes will contribute remarkable peaks for the radial and axial disturbance forces. The proposed dynamic vibration absorber is capable to suppress the high-frequency disturbance forces efficiently under different rotational speeds.
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Nakajima, Kunito, Noah Utsumi, Yoshihisa Saito, and Masashi Yoshida. "Deformation Property and Suppression of Ultra-Thin-Walled Rectangular Tube in Rotary Draw Bending." Metals 10, no. 8 (August 10, 2020): 1074. http://dx.doi.org/10.3390/met10081074.
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Recently, miniaturization and weight reduction have become important issues in various industries such as automobile and aerospace. To achieve weight reduction, it is effective to reduce the material thickness. Generally, a secondary forming process such as bending is performed on the tube, and it is applied as a structural member for various products and a member for transmitting electromagnetic waves and fluids. If the wall thickness of this tube can be thinned and the bending technology can be established, it will contribute to further weight reduction. Therefore, in this study, we fabricated an aluminum alloy rectangular tube with a height H0 = 20 mm, width W0 = 10 mm, wall thickness t0 = 0.5 mm (H0/t0 = 40) and investigated the deformation properties in the rotary draw bending. As a result, the deformation in the height direction of the tube was suppressed applying the laminated mandrel. In contrast, it was found that the pear-shaped deformation peculiar to the ultra-thin wall tube occurs. In addition, axial tension and lateral constraint were applied. Furthermore, the widthwise clearance of the mandrel was adjusted to be bumpy. As a result, the pear-shaped deformation was suppressed, and a more accurate cross-section was obtained.
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Teoh, Choe-Yung, and Zaidi MohdRipin. "Dither effect on drum brake squeal." Journal of Vibration and Control 23, no. 7 (August 9, 2016): 1057–72. http://dx.doi.org/10.1177/1077546315597117.
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This paper describes the dither control system used for suppressing drum brake squeal. The dither force is generated by a piezoceramic actuator installed on the back plate of a drum brake system and successfully quenches the drum brake squeal to background noise level above the critical dither actuation level. The dither is represented as a forcing function in sine waveform in a bi-axial two degrees of freedom mathematical model of drum brake squeal. The model parameters are based on the complex eigenvalue obtained from the mobility measurement and verified with the measured frequency response function. The numerical results show that dither control is more efficient at low sliding speed where lower dither force is needed to quench the brake squeal. Both measured and simulated results show that dither tends to excite the sidebands of the squeal peak with equal frequency spacing at both sides, and these sidebands shift closer to the squeal peak with increase in the dither actuation force.
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Sidharta, Nicholas, and Almanzo Arjuna. "Study on the effect of various burnable poisons on pebble bed reactor with OTTO fuelling schemes using Serpent 2 Monte Carlo code." IOP Conference Series: Earth and Environmental Science 927, no. 1 (December 1, 2021): 012018. http://dx.doi.org/10.1088/1755-1315/927/1/012018.
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Abstract Pebble bed reactor with a once-through-then-out fuelling scheme has the advantage of simplifying the refueling system. However, the core upper-level power density is relatively higher than the bottom, producing an asymmetric core axial power distribution. Several burnable poison (BP) configurations are used to flatten the peak power density and improve power distribution while suppressing the excess core reactivity at the beginning of the burnup cycle. This study uses HTR-PM, China’s pebble bed reactor core, to simulate several burnable poison (BP) configurations. Serpent 2 coupled with Octave and a discrete element method simulation is used to model and simulate the pebble bed reactor core. It is found that erbium needs a large volumetric fraction in either QUADRISO or distributed BP to perform well. On the other hand, gadolinium and boron need a smaller volumetric fraction but perform worse in radial power distribution criteria in the fuel sphere. This study aims to verify the effect of BP added fuel pebbles on an OTTO refueling scheme HTR-PM core axial power distribution and excess reactivity.
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Okui, Tsutomu, and Akifumi Yamaji. "PRELIMINARY POWER TRANSIENT ANALYSIS OF THE SUPER FR WITH AXIALLY HETEROGENEOUS CORE." EPJ Web of Conferences 247 (2021): 07002. http://dx.doi.org/10.1051/epjconf/202124707002.
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The Super FR is one of the SuperCritical Water cooled Reactor (SCWR) concepts with once-through direct cycle plant system. Recently, new design concept of axially heterogeneous core has been proposed, which consists of multiple layers of MOX and blanket fuels. To clarify the safety performance during power transient, safety analyses have been conducted for uncontrolled control rod (CR) withdrawal and CR ejection at full power. RELAP/SCDAPSIM code was used for the safety analysis. The results show that the peak cladding surface temperature (PCST) is high in the upper MOX fuel layer. It is also shown that axial temperature gradient of cladding greatly increases in a short period. Suppressing such large temperature gradient may be a design issue for the axially heterogeneous core from the viewpoint of ensuring fuel integrity.
Conference papers on the topic "Axial peak suppression"
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GUO, Yanchao, Limin GAO, Lei WANG, and Xiaochen MAO. "Effect of axial slot casing treatment on a counter-rotating axial compressor performance and stability." In GPPS Xi'an21. GPPS, 2022. http://dx.doi.org/10.33737/gpps21-tc-133.
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For the purpose of exploring the stall margin improvement capacity potential of axial slot casing treatment (ASCT) technology in the axial counter-rotating compressor (CRAC), the effects of ASCT position and radial deflection angle on the overall performance and stall margin of the counter-rotating axial compressor were studied by numerical method. To reveal the stability expansion mechanism of ASCT in a counter-rotating axial compressor and the effect of casing treatment on the rotor/rotor interference effect between the front and rear rotors. The results show that the axial slot position has little effect on stall margin improvement, but has a great influence on peak efficiency. The peak efficiency loss can be reduced by increasing the radial deflection angle of the ASCT. The stall margin can be improved by about 10% by arranging the ASCT on the rear rotor. The suppression of tip leakage flow by axial slot and the transport of low-energy fluid in tip region can delay the occurrence of the stall, but the mixing of flow in slot increases the efficiency loss.
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Chen, Huang, Yuanchao Li, and Joseph Katz. "On the Interactions of a Rotor Blade Tip Flow With Axial Casing Grooves in an Axial Compressor Near the Best Efficiency Point." In ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-77071.
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Previous studies have shown that axial casing grooves (ACGs) are effective in delaying the onset of stall, but degrade the performance of axial turbomachines around the best efficiency point (BEP). Our recent experimental study [1] in the JHU refractive index-matched liquid facility have examined the effects of ACGs on delaying stall of a one and half stage compressor. The semicircular ACGs based on Müller et al. [2] reduce the stall flow rate by 40% with a slight decrease in pressure rise at higher flow rates. Stereo-PIV (SPIV) measurements at a flow rate corresponding to the pre-stall condition of the untreated machine have identified three flow features that contribute to the delay in stall. Efficiency measurements conducted as part of the present study show that the ACGs cause a 2.4% peak efficiency loss. They are followed by detailed characterizations of the impact of the ACGs on the flow structure and turbulence in the tip region at high flow rates away from stall. Comparisons with the flow structure without casing grooves and at low flow rate are aimed at exploring relevant flow features that might be associated with the reduced efficiency. The SPIV measurements in several meridional and radial planes show that the periodic inflow into the groove peaks when the rotor blade pressure side (PS) overlaps with the downstream end of the groove, but diminishes when this end faces the blade suction side (SS). The inflow velocity magnitude is substantially lower than that occurring at a flow rate corresponding to the pre-stall conditions of the untreated machine. Yet, entrainment of the PS boundary layer and its vorticity during the inflow phase generates counter-rotating radial vortices at the entrance to the groove, and a “discontinuity” in the appearance of the tip leakage vortex (TLV). While being exposed to the blade SS, the backward tip leakage flow causes flow separation and formation of a counter-rotating vortex at the downstream corner of the groove, which migrates towards the passage with increasing flow rate. Interactions of this corner vortex with the TLV cause fragmentation of the latter, creating a broad area with secondary flows and elevated turbulence level. Consequently, the vorticity shed from the blade tip remains scattered from the groove corner to the blade tip long after the blade clears this groove. The turbulence peaks around the corner vortex, the TLV, and the shear layer connecting it to the SS corner. During periods of inflow, there is a weak outflow from the upstream end of the groove. At other phases, most of the high secondary flows are confined to the downstream corner, leaving only weak internal circulation in the rest of the groove, but with a growing shear layer with elevated (but weak) turbulence originating from the upstream corner. Compared to a smooth endwall, the groove also increases the flow angle near the blade tip leading edge (LE) and varies it periodically. Accordingly, the magnitude of circulation shed from the blade tip and leakage flow increase near the leading edge. The insight from these observations might guide the development of ACGs that take advantage of the effective stall suppression by the ACGs but alleviate the adverse effects at high flowrates.
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Zhou, Tongming, S. F. Mohd Razali, and Liang Cheng. "Investigation on Suppression of Vortex-Induced Vibration Using Helical Strakes." In ASME 2010 29th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2010. http://dx.doi.org/10.1115/omae2010-20984.
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While the effect of helical strakes on suppression of Vortex-Induced Vibrations (VIV) has been studied extensively, the mechanism of VIV mitigation using helical strakes is less well documented in the literature. In the present study, experiments were conducted in a wind tunnel at four velocities, i.e. 1.92, 3.83, 5.74 and 7.65 m/s. Strakes with a dimension of 10d in pitch and 0.12d in height were fitted onto a rigid cylinder of diameter d = 80mm, and subjected to a transverse air flow. Hotwire techniques were used to measure the instantaneous velocity fluctuations at various locations to explore the mechanism for VIV mitigation by using helical strakes. It was found that the helical strakes reduce VIV by about 98%. Unlike the bare cylinder which experiences lock-in over the reduced velocity of 5 ∼ 9, the straked cylinder does not show any lock-in region. In exploring the mechanism of VIV reduction by helical strakes, it was found that vortices shed from the straked cylinder are weakened significantly. The dominant frequency of the vortex structures along the spanwise direction of the bare cylinder was very stable. This is not the case for the straked cylinder wake, which differs by about 36% of the averaged peak frequency over the length of 3.125d along the cylinder axial direction, indicating that the vortex shed from the latter is out-of-phase and mismatching. This is supported by the phase shift between the velocity signals measured at two locations separated in the spanwise direction. The cross-correlation coefficients in the bare cylinder wake were much larger than that obtained in the straked cylinder wake, indicating that the correlation length of the former is much larger than that of the latter.
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Law, Yun Zhi, and Rajeev K. Jaiman. "Staggered Grooves for the Suppression of Vortex-Induced Vibration in Flexible Cylinders." In ASME 2019 38th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/omae2019-95649.
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Abstract Vortex-Induced Vibration (VIV) remains a challenge to the offshore structures such as deepwater riser and subsea pipelines, which require a robust and cost-effective control to circumvent the impact of the dynamic loads and the fatigue damage. While the state-of-the-art helical strakes are effective in the suppression of VIV amplitudes, they cause a higher drag force and bending moment on the submerged structure. In this work, we numerically investigate the recently proposed staggered groove concept to reduce both the VIV amplitudes and the drag force. The staggered groove is constructed by aligning the square grooves alternatively along the spanwise (axial) direction of the cylinder. The performance of the staggered groove concept is examined in three dimensions for two VIV configurations at subcritical Reynolds number (Re) namely: (i) two-degree-of-freedom elastically mounted rigid cylinder (Re = 3000–10000), and (ii) pinned-pinned flexible cylinder in a uniform current flow at Re = 4800. Their characteristic responses and the vortex dynamics are compared to their plain cylinder counterparts. For the two VIV configurations, our results show a remarkable reduction of both the peak vibration amplitude and the drag force up to 40% and 20%, respectively. Further analysis has shown that such reduction is related to the diminishing of the spanwise correlation of hydrodynamic forces due to the alternating alignment of the grooves. Such effect on the spanwise correlation leads to the broadening of the frequency spectra of the forces, thereby reduces the average power transferred to the cylinder and leads to the VIV suppression.
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Chen, Huang, Subhra Shankha Koley, Yuanchao Li, and Joseph Katz. "Systematic Experimental Evaluations Aimed at Optimizing the Geometry of Axial Casing Groove in a Compressor." In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-91050.
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Abstract Performance and flow measurements are carried out to investigate the impact of varying the geometry of axial casing grooves on the stall margin and efficiency of an axial turbomachine. Prior studies have shown that skewed semi-circular grooves installed near the blade leading edge (LE) have multiple effects on the flow structure, including ingestion of the tip leakage vortex (TLV), suppression of backflow vortices, and periodic variations of flow angle. To determine which of these phenomena is a key contributor, the present study examines the impact of several grooves, all with the same inlet geometry, but with outlets aimed at different directions. The “U” grooves that have circumferential exits aimed against the direction of blade rotation achieve the highest stall margin improvement of well above 60% but cause a 2.0% efficiency loss near the best efficiency point (BEP). The “S” grooves, which have exits aimed with the blade rotation, achieve a relatively moderate stall margin improvement of 36%, but they do not reduce the BEP efficiency. Other grooves, which are aligned with and against the flow direction at the exit from upstream inlet guide vanes, achieve lower improvements. These trends suggest that causing high periodic variations in flow angle around the blade leading edge is particularly effective in extending the stall margin, but also reduces the peak efficiency. In contrast, maintaining low flow angles near the LE achieves more moderate improvement in stall margin, without the maximum efficiency loss. Hence, of the geometries tested, the S grooves appear to have the best overall impact on the machine performance. Velocity measurements and flow visualizations are performed in an axial plane located downstream of the grooves, near the trailing edge of the rotor. Reduced efficiency or performance co-occurs with elevated circumferential velocity in the tip region, but differences in the axial blockage are subtle. Yet, near the BEP, the regions with reduced axial velocity, or even negative velocity between the TLV and the endwall, are wider behind the U grooves compared to the S grooves. The vorticity profiles also show that at low flow rates the TLV is ingested entirely by the grooves, in contrast to the best efficiency point, where a considerable fraction of the TLV rollup occurs downstream of the grooves.
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Farag, Ashraf, Terry Ng, Dan Olson, and Jeffrey Hammersley. "Effect of Different Geometric Parameters on the Flow Characteristics in a Symmetric Bifurcation Model." In ASME 1998 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/imece1998-0049.
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Abstract Steady divergent flow (inspiratory directed) is measured using Laser Doppler Velocimetry in large scale models carefully mimicing the morphometry of small human airways. We Evaluated the anatomical features which induced vorticity in the flow from a vorticity free entrance, under conditions of convective similitude (simultaneous Reynolds And Dean’s Numbers). Five symmetrical bifurcation models with different bifurcation angles and curvature ratios are tested. A flow separation (carina) in each model is shaped to anatomical measures and the conformation of the transition between parent and daughter branches representing the morphmetric mean shape defined from casts of human airways. The flow pattern in the daughter tubes is typical of laminar flow within the entrance (diameter/axial length < 5) to sharp bends (Dean number > 500), with rapid development of strong secondary flows (maximum secondary velocity is 40% of mean axial velocity) consisting of two main vortices, with two smaller and weaker secondary vortex activities towards the inner wall of curvature. These may be time dependent interrelation with these vortices causing warbling at specific flow conditions. The calculated vorticity transport along the flow axis showed interaction between the viscous forces at the new boundary layer development along the carinal wall and centrifugal forces of curvature, with a significant influence by the upstream flow prior to the entering the actual flow division. This interplay resulted in an overshoot of the calculated vorticity transport comparable to flow entering curved bends an a suppression for the tendency to separate at the inner wall of these tight bends. The maximum primary flow velocities are skewed towards the carinal side (outer wall of curvature) and development of a second peak occurred with convection of the higher velocity elements towards the inner wall of curvature by the strong secondary flow. The appearance of the second peak depends mainly on the curvature ratio of the daughter tubes. This study is the “baseline” observation for a airway structure to function analysis. The observed flow patterns have high influence on conductive mixing, particle deposition, volume flow distribution, gaseous scrubbing (absorption at the liquid wall surfaces), and conductive-diffusive axial dispersion mechanism; all critical features for respiration. Detailed velocity measurements are carried out in all models at different axial locations. The locations are chosen according to the expected rate of velocity alterations in the models. Figures 1 to 4 show some typical primary and secondary velocities in models 1 (1/7 curvature ration and 70° bifurcation angle) and 4 (1/14 curvature ratio and 70° bifurcation angle at Reynolds number of 1500 based on the parent tube diameter. As can be seen in Figures 1 and 2, the second peak is not observed in model 4 while it is clearly observed in model 1.
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Shankha Koley, Subhra, Huang Chen, Ayush Saraswat, and Joseph Katz. "Effect of Axial Casing Groove Geometry on Rotor-Groove Interactions in the Tip Region of a Compressor." In ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-14696.
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Abstract The present experimental study expands an ongoing effort to characterize the interactions of axial casing grooves (ACGs) with the flow in the tip region of an axial turbomachine. In recent work, we have tested a series of grooves with the same inlet geometry that overlaps with the rotor blade leading edge, but with different exit directions. Two geometries have stood out: The U grooves, which have an outflow in the negative circumferential direction (opposing the blade motion) are the most effective in suppressing stall, achieving as much as 60% reduction in stall flowrate, but cause a 2% decrease in efficiency around the best efficiency point (BEP). In contrast, the S grooves, which have an outflow in the positive circumferential direction, achieve a milder improvement in stall suppression (36%) but do not degrade the performance near BEP. This paper focuses on explaining these trends by measuring the flow in the tip region and within the U and S grooves. The stereo-PIV (SPIV) measurements are performed in the JHU refractive index matched facility, which allows unobstructed observations in the entire machine. Data has been acquired in two meridional planes that intersect with the grooves at different locations, and two radial planes (z, θ), the first coinciding with the blade tip, and the second, with the tip gap. For each plane, data has been acquired at fourteen rotor orientations relative to the grooves to examine the rotor-grooves interactions. At low flow rates, the inflow into both grooves peaks periodically when the blade pressure side (PS) faces the entrance (downstream side) to the grooves. This inflow rolls up into a large vortex that remains and lingers within the groove long after the blade clears the groove. The outflow depends on the shape of the groove. For the S groove, the outflow exits at the upstream end of the groove in the positive circumferential direction, as designed. In contrast, for the U grooves, the fast radially and circumferentially negative outflow peaks at the base of the U. The resulting jet causes substantial periodic variations in the flow angle near the leading edge of the rotor blade. Close to the BEP, the chordwise location of primary blade loading moves downstream, as expected. The inflow into the grooves occurs for a small fraction of the blade passing period, and most of the tip leakage vortex remains in the main flow passage. For the S grooves, the rotor-groove interactions seem to be minimal, with little (but not zero) inflow or outflow at both ends, and minimal changes to the flow angle in the passage. In contrast, for the U groove, the inflow into and outflow from the groove reverse direction (compared to the low flowrate trends), entering at the base of the U, and exiting mostly at its downstream end, especially when the blade is not near. The resulting entrainment of secondary flows from the groove into the passage are likely contributors to the reduced efficiency at BEP for the U grooves.
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Chen, Huang, Yuanchao Li, Subhra Shankha Koley, Nick Doeller, and Joseph Katz. "An Experimental Study of Stall Suppression and Associated Changes to the Flow Structures in the Tip Region of an Axial Low Speed Fan Rotor by Axial Casing Grooves." In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-65099.
Full textAbstract:
The effects of axial casing grooves on the performance and flow structures in the tip region of an axial low speed fan rotor have been studied experimentally in the JHU refractive index-matched liquid facility. The four-per-passage semicircular grooves are skewed by 45° in the positive circumferential direction, and have a diameter of 65% of the rotor blade axial chord length. A third of the groove overlaps with the blade front, and the rest extends upstream. These grooves have a dramatic effect on the machine performance, reducing the stall flow rate by 40% compared to the same machine with a smooth endwall. However, they reduce the pressure rise at high flow rates. The flow characterization consists of qualitative visualizations of vortical structures using cavitation, as well as stereo-PIV (SPIV) measurements in several meridional and (z,θ) planes covering the tip region and interior of the casing grooves. The experiments are performed at a flow rate corresponding to pre-stall conditions for the untreated machine. They show that the flow into the downstream sides of the grooves and the outflow from their upstream sides vary periodically. The inflow peaks when the downstream end is aligned with the pressure side (PS) of the blade, and decreases, but does not vanish, when this end is located near the suction side (SS). These periodic variations have three primary effects: First, substantial fractions of the leakage flow and the tip leakage vortex (TLV) are entrained periodically into the groove. Consequently, in contrast to the untreated flow, The TLV remnants remain confined to the vicinity of the entrance to the groove, and the TLV strength diminishes starting from the mid-chord. Second, the grooves prevent the formation of large scale backflow vortices (BFVs), which are associated with the TLV, propagate from one blade passage to the next, and play a key role in the onset of rotating stall in the untreated fan. Third, the flow exiting from the grooves causes periodic variations of about 10° in the relative flow angle around the blade leading edge, presumably affecting the blade loading. The distributions of turbulent kinetic energy provide statistical evidence that in contrast to the untreated casing, very little turbulence originating from a previous TLV, including the BFVs, propagates from the PS to the SS of the blade. Hence, the TLV-related turbulence remain confined to the entrance to groove. Elevated, but lower turbulence is also generated as the outflow from the groove jets into the passage.
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Zhu, Mingmin, Xiaoqing Qiang, and Jinfang Teng. "Numerical Investigation on Slot Casing Treatment in a Transonic Axial Compressor Stage: Part 1 — Casing Treatment Design." In ASME 2016 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/imece2016-65260.
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Slot-type casing treatment generally has a great potential of enhancing the operating range for tip-critical compressor rotors, however, with remarkable efficiency drop. Part I of this two-part paper was committed to develop a slot configuration with desired stall margin improvement and minimized efficiency loss. Steady simulation was carried out in a 1.5 transonic axial compressor stage at part design rotating speed. At this rotating speed this compressor stage operated at a subsonic condition and showed a rather narrow operating range, which needed to be improved badly. Flow fields analysis at peak efficiency and near stall point showed that the development of tip leakage vortex and resulting blockage near casing resulted in numerical stall. Three kinds of skewed slots with same rotor exposure and casing porosity were designed according to the tip flow field and some empirical strategies. Among three configurations, arc-curved skewed slot showed minimum peak efficiency drop with considerable stall margin improvement. Then rotor exposure and casing porosity were varied based on the original arc-curved skewed slot, with a special interest in detecting their impact on the compressor stability and overall efficiency. Result showed that smaller rotor exposure and casing porosity leaded to less efficiency drop. But meanwhile, effectiveness of improving compressor stability was weakened. The relation between efficiency drop and stall margin improvement fell on a smooth continuous curve throughout all slots configurations, indicating that the detrimental effect of casing treatment on compressor was inevitable. Flow analysis was carried out for cases of smooth casing and three arc-curved configurations at smooth casing near stall condition. The strength of suction/injection, tip leakage flow behavior and removal of blockage near casing were detailed examined. Larger rotor tip exposure and slots number contributed to stronger injection flow. The loss generated within the mixing process of injection flow with main flow and leakage flow is the largest source of entropy increase. Further loss mechanisms were interpreted at eight axial cuts, which were taken through the blade row and slots to show the increase in entropy near tip region. Entropy distributions manifested that loss generations with smooth casing were primarily ascribed to low-momentum tip leakage flow/vortex and suction surface separation at leading edge. CU0 slot, the arc-curved slots with 50% rotor tip exposure, was capable of suppressing the suction surface separation loss. Meanwhile, accelerated tip leakage flow brought about additional loss near casing and pressure surface. Upstream high entropy flow would be absorbed into the rear portion of slots repeatedly, resulting in further loss.
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Behjat, Amir, Manaswin Oddiraju, Mohammad Ali Attarzadeh, Mostafa Nouh, and Souma Chowdhury. "Metamodel Based Forward and Inverse Design for Passive Vibration Suppression." In ASME 2020 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/detc2020-22747.
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Abstract Aperiodic metamaterials represent a class of structural systems that are composed of different building blocks (cells), instead of a self-repeating chain of the same unit cells. Optimizing aperiodic cellular structural systems thus presents high-dimensional design problems, that become intractable to solve using purely high-fidelity structural analysis coupled with optimization. Specialized analytical modeling along with metamodel based optimization can provide a more tractable alternative to designing such aperiodic metamaterials. To explore this concept, this paper presents an initial design automation framework applied to a case study representative of a simple 1D metamaterial system. The case under consideration is a drill string, where vibration suppression is of utmost importance. The drill string comprises a set of nonuniform rings attached to the outer surface of a longitudinal rod. As such, the resultant system can now be perceived as an aperiodic 1D metamaterial with each ring/gap representing a cell. Despite being a 1D system, the simultaneous consideration of multiple degrees of freedom (associated with torsional, axial, and lateral motions) poses significant computational challenges. To deal with these challenges, a transfer matrix method (TMM) is employed to analytically determine the frequency response of the drill string. However, due to the minute scale cost of the TMM method, the optimization remains computationally burdensome. This latter challenge is addressed by training a suite of neural networks on a set of TMM samples, with each network providing the response w.r.t. a specific frequency. Optimization is then performed to minimize mass subject to constraints on the gap between consecutive resonance peaks in one case, and minimizing this gap in the second case. Crucial improvements are accomplished over the initial baselines in both cases. Further novel contributions occur through the development of an inverse modeling approach that can learn optimal inverse designs with minimum mass and a desirable non-resonant frequency range, which partially mimics band gap behavior in perfectly periodic dispersive structures. To this end, we introduce the use of an emerging modeling formalism called in-vertible neural nets. Our study indicates that the inverse model is able to generate constraint satisfying designs with slightly higher mass.