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Статті в журналах з теми "Averaged dimensionless parameters"
1
Simon, Frederick F. "The Use of Transition Region Characteristics to Improve the Numerical Simulation of Heat Transfer in Bypass Transitional Flows." International Journal of Rotating Machinery 2, no. 2 (1995): 93–102. http://dx.doi.org/10.1155/s1023621x95000248.
Повний текст джерелаАнотація:
A method is presented for improving the numerical prediction of bypass transition heat transfer on a flat plate in a high-disturbance environment with zero or favorable pressure gradient. The method utilizes low Reynolds number k-ε turbulence models in combination with the characteristic parameters of the transition region. The parameters representing the characteristics of the transition region used are the intermittency, transition length and turbulent spot properties. An analysis is made of the transition length in terms of turbulent spot variables. The nondimensional spot formation rate, required for the prediction of the transition length, is shown by the analysis to be a function of the spot spreading angle, the dimensionless spot velocity ratio and the dimensionless spot area ratio. The intermittency form of the k-ε equations was derived from conditionally averaged equations which have been shown to be an improvement over global-time-averaged equations for the numerical calculation of the transition region. The numerical predictions are in general good agreement with the experimental data and indicate the potential use of the method in accelerating flows. Turbulence models of the k-ε type are known to underpredict the transition length. The present work demonstrates how incorporating transition region characteristics improves the ability of two-equation turbulence models to simulate bypass transition for flat plates with potential application to turbine vanes and blades.
2
Whitney, Michael M., Daniel L. Codiga, David S. Ullman, Pearse M. McManus, and Ralph Jiorle. "Tidal Cycles in Stratification and Shear and Their Relationship to Gradient Richardson Number and Eddy Viscosity Variations in Estuaries." Journal of Physical Oceanography 42, no. 7 (July 1, 2012): 1124–33. http://dx.doi.org/10.1175/jpo-d-11-0172.1.
Повний текст джерелаАнотація:
Abstract Tidal cycles in stratification and shear lead to tidal variations in mixing in many estuaries. This study 1) defines readily observable dimensionless parameters for establishing the sense and magnitude of gradient Richardson number Ri and eddy viscosity K changes from maximum to minimum stratification during a tidal cycle and 2) calculates where representative estuaries fit in this parameter space. The dimensionless parameters are Ri calculated with tidal-averaged stratification and shear, scaled stratification amplitude, and a scaled shear parameter. The scaled stratification amplitude is approximately the tidal amplitude of stratification divided by the tidal-averaged stratification. The scaled shear parameter depends on the scaled tidal amplitude of shear and the phase difference between the tidal cycles of stratification and shear. Over most of the parameter space, Ri is larger at maximum stratification. If the scaled stratification amplitude falls below a threshold value defined in terms of the scaled shear parameter, shear effects dominate and cause Ri to be greater at minimum stratification. Two-thirds of the selected estuary locations have greater Ri at maximum stratification. The remaining locations are dominated by shear differences and have an atypical mixing cycle with greater Ri at minimum stratification. The Ri and K tidal variations and the position in the parameter space can drastically shift with the spring–neap cycle and spatial variations within an estuary.
3
Pavlenko, Ivan, Oleksandr Liaposhchenko, Marek Ochowiak, Radosław Olszewski, Maryna Demianenko, Oleksandr Starynskyi, Vitalii Ivanov, Vitalii Yanovych, Sylwia Włodarczak, and Michał Doligalski. "Three-Dimensional Mathematical Model of the Liquid Film Downflow on a Vertical Surface." Energies 13, no. 8 (April 15, 2020): 1938. http://dx.doi.org/10.3390/en13081938.
Повний текст джерелаАнотація:
Film downflow from captured liquid without wave formation and its destruction is one of the most important aspects in the development of separation equipment. Consequently, it is necessary to create well-organized liquid draining in areas of captured liquid. Thus, the proposed 3D mathematical model of film downflow allows for the determination of the hydrodynamic parameters of the liquid film flow and the interfacial surface. As a result, it was discovered that the interfacial surface depends on the proposed dimensionless criterion, which includes internal friction stress, channel length, and fluid density. Additionally, equations for determining the averaged film thickness, the averaged velocity vectors over the film thickness, the longitudinal and vertical velocity components, and the initial angle of streamline deviation from the vertical axis were analytically obtained.
4
Moukhtari, Fatima-Ezzahra, and Brice Lecampion. "A semi-infinite hydraulic fracture driven by a shear-thinning fluid." Journal of Fluid Mechanics 838 (January 25, 2018): 573–605. http://dx.doi.org/10.1017/jfm.2017.900.
Повний текст джерелаАнотація:
We use the Carreau rheological model which properly accounts for the shear-thinning behaviour between the low and high shear rate Newtonian limits to investigate the problem of a semi-infinite hydraulic fracture propagating at a constant velocity in an impermeable linearly elastic material. We show that the solution depends on four dimensionless parameters: a dimensionless toughness (function of the fracture velocity, confining stress, material and fluid parameters), a dimensionless transition shear stress (related to both fluid and material behaviour), the fluid shear-thinning index and the ratio between the high and low shear rate viscosities. We solve the complete problem numerically combining a Gauss–Chebyshev method for the discretization of the elasticity equation, the quasi-static fracture propagation condition and a finite difference scheme for the width-averaged lubrication flow. The solution exhibits a complex structure with up to four distinct asymptotic regions as one moves away from the fracture tip: a region governed by the classical linear elastic fracture mechanics behaviour near the tip, a high shear rate viscosity asymptotic and power-law asymptotic region in the intermediate field and a low shear rate viscosity asymptotic far away from the fracture tip. The occurrence and order of magnitude of the extent of these different viscous asymptotic regions are estimated analytically. Our results also quantify how shear thinning drastically reduces the size of the fluid lag compared to a Newtonian fluid. We also investigate simpler rheological models (power law, Ellis) and establish the small domain where they can properly reproduce the response obtained with the complete rheology.
5
Zhao, T. S., and P. Cheng. "Oscillatory Heat Transfer in a Pipe Subjected to a Laminar Reciprocating Flow." Journal of Heat Transfer 118, no. 3 (August 1, 1996): 592–97. http://dx.doi.org/10.1115/1.2822673.
Повний текст джерелаАнотація:
An experimental and numerical study has been carried out for laminar forced convection in a long pipe heated by uniform heat flux and subjected to a reciprocating flow of air. Transient fluid temperature variations in the two mixing chambers connected to both ends of the heated section were measured. These measurements were used as the thermal boundary conditions for the numerical simulation of the hydrodynamically and thermally developing reciprocating flow in the heated pipe. The coupled governing equations for time-dependent convective heat transfer in the fluid flow and conduction in the wall of the heated tube were solved numerically. The numerical results for time-resolved centerline fuid temperature, cycle-averaged wall temperature, and the space-cycle averaged Nusselt number are shown to be in good agreement with the experimental data. Based on the experimental data, a correlation equation is obtained for the cycle-space averaged Nusselt number in terms of appropriate dimensionless parameters for a laminar reciprocating flow of air in a long pipe with constant heat flux.
6
Sharifi, S., M. Sterling, and D. W. Knight. "A novel application of a multi-objective evolutionary algorithm in open channel flow modelling." Journal of Hydroinformatics 11, no. 1 (January 1, 2009): 31–50. http://dx.doi.org/10.2166/hydro.2009.033.
Повний текст джерелаАнотація:
The Shiono and Knight method (SKM) is a simple depth-averaged flow model, based on the RANS equations which can be used to estimate the lateral distributions of depth-averaged velocity and boundary shear stress for flows in straight prismatic channels with the minimum of computational effort. However, in order to apply the SKM, detailed knowledge relating to the lateral variation of the friction factor (f), dimensionless eddy viscosity (λ) and a sink term representing the effects of secondary flow (Γ) are required. In this paper a multi-objective evolutionary algorithm is used to study the lateral variation and value of these parameters for simple trapezoidal channels over a wide range of aspect ratios through the model calibration process. Based on the available experimental data, four objectives are selected and the NSGA-II algorithm is applied to several datasets. The best answer for each set is then selected based on a proposed methodology. Rules relating f, λ and Γ to the wetted parameter ratio (Pb/Pw) for a variety of situations have been developed which provide practical guidance for the engineer on choosing the appropriate parameters in the SKM model.
7
Quinn, Daniel B., George V. Lauder, and Alexander J. Smits. "Scaling the propulsive performance of heaving flexible panels." Journal of Fluid Mechanics 738 (December 5, 2013): 250–67. http://dx.doi.org/10.1017/jfm.2013.597.
Повний текст джерелаАнотація:
AbstractWe present an experimental investigation of flexible panels actuated with heave oscillations at their leading edge. Results are presented from kinematic video analysis, particle image velocimetry, and direct force measurements. Both the trailing edge amplitude and the mode shapes of the panel are found to scale with dimensionless parameters originating from the Euler–Bernoulli beam equation. The time-averaged net thrust increases with heaving frequency, but experiences localized boosts near resonant frequencies where the trailing edge amplitude is maximized. These boosts correspond to local maxima in the propulsive efficiency. For a constant heave amplitude, the time-averaged net thrust coefficient is shown to be a function of Strouhal number over a wide range of conditions. It appears, therefore, that self-propelled swimming (zero net thrust) only occurs over a small range of Strouhal numbers. Under these near-constant Strouhal number conditions, the propulsive economy increases with higher flexibilities and slower swimming speeds.
8
Stone, L. D., and R. J. Goldstein. "Film Cooling Effectiveness Data for Simple Injection Geometries: A Collection of Three-Axis Plots." International Journal of Rotating Machinery 1, no. 1 (1994): 73–81. http://dx.doi.org/10.1155/s1023621x94000072.
Повний текст джерелаАнотація:
A three-axis plot of laterally averaged film cooling effectiveness versus blowing rate and versus dimensionless distance downstream is a sufficiently compact representation of film cooling effectiveness data for injection through a row of holes or two rows of holes to enable easy, global comparisons among a variety of data sets. By plotting data from several film cooling studies conducted at the University of Minnesota, the dominant roles played by density ratio, hole spacing, and surface curvature become apparent. It is also seen that a slot-plate prediction/correlation from two-dimensional film cooling studies makes an excellent standard of comparison for all film cooling studies, even though the more commonly encountered (two-axis) comparisons using standardized nondimensional parameters do not usually suggest this.
9
Lenci, Alessandro, and Vittorio Di Federico. "Shear-Thinning Fluid Flow in Variable-Aperture Channels." Proceedings 48, no. 1 (November 12, 2019): 28. http://dx.doi.org/10.3390/ecws-4-06426.
Повний текст джерелаАнотація:
Non-Newtonian fluid flow in a single fracture is a 3D nonlinear phenomenon that is often averaged across the fracture aperture and described as 2D. To capture key interactions between fluid rheology and spatial heterogeneity, we adopted a simplified geometric model to describe aperture variability, consisting of adjacent one-dimensional channels with constant aperture, each drawn from assigned aperture distribution. The flow rate was then derived under the lubrication approximation for the two limiting cases of an external pressure gradient that was parallel/perpendicular to the channels; these two arrangements provided an upper/lower bound to fracture conductance. Fluid rheology was described via the Prandtl–Eyring shear-thinning model. Novel closed-form results for flow rate and hydraulic aperture were derived and are discussed; different combinations of parameters describing the fluid rheology and variability of the aperture field were considered. In general, flow rate depends, in a nonlinear fashion, on the dimensionless pressure gradient and distribution parameters.
10
Ivchenko, V. O., S. Danilov, B. Sinha, and J. Schröter. "Integral Constraints for Momentum and Energy in Zonal Flows with Parameterized Potential Vorticity Fluxes: Governing Parameters." Journal of Physical Oceanography 44, no. 3 (March 1, 2014): 922–43. http://dx.doi.org/10.1175/jpo-d-13-0173.1.
Повний текст джерелаАнотація:
Abstract Integral constraints for momentum and energy impose restrictions on parameterizations of eddy potential vorticity (PV) fluxes. The impact of these constraints is studied for a wind-forced quasigeostrophic two-layer zonal channel model with variable bottom topography. The presence of a small parameter, given by the ratio of Rossby radius to the width of the channel, makes it possible to find an analytical/asymptotic solution for the zonally and time-averaged flow, given diffusive parameterizations for the eddy PV fluxes. This solution, when substituted in the constraints, leads to nontrivial explicit restrictions on diffusivities. The system is characterized by four dimensionless governing parameters with a clear physical interpretation. The bottom form stress, the major term balancing the external force of wind stress, depends on the governing parameters and fundamentally modifies the restrictions compared to the flat bottom case. While the analytical solution bears an illustrative character, it helps to see certain nontrivial connections in the system that will be useful in the analysis of more complicated models of ocean circulation. A numerical solution supports the analytical study and confirms that the presence of topography strongly modifies the eddy fluxes.
Дисертації з теми "Averaged dimensionless parameters"
1
Рєзва, Ксенія Сергіївна. "Удосконалення проточних частин високонапірних оборотних гідромашин на основі чисельного моделювання їх гідродинамічних характеристик". Thesis, Національний технічний університет "Харківський політехнічний інститут", 2019. http://repository.kpi.kharkov.ua/handle/KhPI-Press/40009.
Повний текст джерелаАнотація:
Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.05.17 – гідравлічні машини і гідропневмоагрегати. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2019 р.
Дисертацію присвячено вирішенню науково-практичної задачі удосконалення проточних частин високонапірних оборотних гідромашин за рахунок розробки методів розрахунку та аналізу їх гідродинамічних характеристик. На підставі розгляду тенденцій розвитку гідроенергетики України, з урахуванням ролі високонапірних оборотних гідромашин в об'єднаній енергетичній системі, відмічено актуальність проектування нових проточних частин. Визначено переваги та недоліки існуючих методів дослідження гідродинамічних процесів у проточних частинах оборотних гідромашин. Наведені результати розрахунку гідродинамічних характеристик елементів проточної частини на основі методу осереднених безрозмірних параметрів для оборотних гідромашин ОРО200-В-100 та ОРО500-В-100. Застосована математична модель робочого процесу гідромашини на основі блочно-ієрархічного підходу для проведення дослідження балансу енергії. Визначено вплив геометричних параметрів елементів проточної частини на показники роботи. Проведено чисельне дослідження просторової течії рідини в проточній частині високонапірних оборотних гідромашин за допомогою CFD, що дозволило визначити та візуалізувати картину течії. Складено баланси енергії гідромашин ОРО200-В-100 та ОРО500-В-100. Відмічено, що розподіл втрат по елементам проточної частини нерівномірний: для ОРО200-В-100 найбільшу частину втрат складають втрати в робочому колесі (близько 56 %), для ОРО500-В-100 – втрати у підводі (близько 62 %). Описано основні положення визначення оптимального режиму роботи оборотної гідромашини. Запропоновано та досліджено модифікований підвід для тихохідної оборотної гідромашини ОРО500-В-100, щоб підвищити її енергетичні показники: краще узгоджені елементи ПЧ та гідравлічний ККД збільшився на 2 %.Thesis for granting the Degree of Candidate of Technical sciences in speciality 05.05.17 – Hydraulic machines and hydropneumatic units. – National Technical University "Kharkiv Polytechnic Institute", 2019. The tеhesis is devoted to the solution of the scientific and practical problem of improvement of the water passages of the high-pressure reversible hydraulic due to calculation and analysis their hydrodynamic characteristics. Based on the review of the trends in the development of hydropower engineering in Ukraine and given the role of high-pressure reversible hydraulic machines in the United Power System, it was noted that the designing a new flow parts is topical task. Advantages and disadvantages of the existing methods for research hydrodynamic processes in water passages of reversible hydraulic machines were identified after their analysis. The results of the calculation of the hydrodynamic characteristics of the elements of the water passages based on the method of averaged dimensionless parameters using the example of reversible hydraulic machines OPO200-B-100 and OPO500-B-100 were demonstrated. The mathematical model of the hydraulic machine working process based on a block-hierarchical approach was used to study the energy balance in the turbine and pump modes of hydraulic machines. The influence of the geometrical parameters of the elements of the water passage on the performance was determined: how the angle of flow in the spiral casing (cп ), the height of the wicket gate (b0 D) and the shape of the wicket gate profile influence the value of the coefficient resistance in the wicket gate. A numerical study of the three-dimensional flow of fluid in the water passage of high-pressure reversible hydraulic machines was carried out using the CFD software. This program allows determining the character of the flow and presenting the fields of distribution of velocity components, pressure and streamlines. The balances of energy were compiled: for the OPO200-B-100 in the turbine and pump operation modes, for the OPO500-B-100 in the turbine operation mode. It is noted that the distribution of losses on the elements of the water passage is not uniform: for the OPO200-B-100, the greatest part of the total losses are losses in the runner (about 56%), for OPO500-B-100 - losses in the inlet (about 62%). The main points for determining the optimal operating mode of the reversible hydraulic machine are described. The modified inlet for low-speed high-pressure hydraulic machine OPO500-B-100 was proposed and investigated to increase energy performance of hydraulic machine. The spiral casing was expanded, the number of stay vane blades and wicket gate blades were reduced to 16. As a result of the calculations of the modified inlet, the obtained results showed that the second variant made it possible to better align the elements of the water passage and the hydraulic efficiency increased by 2 %.
2
Рєзва, Ксенія Сергіївна. "Удосконалення проточних частин високонапірних оборотних гідромашин на основі чисельного моделювання їх гідродинамічних характеристик". Thesis, Національний технічний університет "Харківський політехнічний інститут", 2018. http://repository.kpi.kharkov.ua/handle/KhPI-Press/40011.
Повний текст джерелаАнотація:
Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.05.17 – гідравлічні машини і гідропневмоагрегати. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2019 р.
Дисертацію присвячено вирішенню науково-практичної задачі удосконалення проточних частин високонапірних оборотних гідромашин за рахунок розробки методів розрахунку та аналізу їх гідродинамічних характеристик. На підставі розгляду тенденцій розвитку гідроенергетики України, з урахуванням ролі високонапірних оборотних гідромашин в об'єднаній енергетичній системі, відмічено актуальність проектування нових проточних частин. Визначено переваги та недоліки існуючих методів дослідження гідродинамічних процесів у проточних частинах оборотних гідромашин. Наведені результати розрахунку гідродинамічних характеристик елементів проточної частини на основі методу осереднених безрозмірних параметрів для оборотних гідромашин ОРО200-В-100 та ОРО500-В-100. Застосована математична модель робочого процесу гідромашини на основі блочно-ієрархічного підходу для проведення дослідження балансу енергії. Визначено вплив геометричних параметрів елементів проточної частини на показники роботи. Проведено чисельне дослідження просторової течії рідини в проточній частині високонапірних оборотних гідромашин за допомогою CFD, що дозволило визначити та візуалізувати картину течії. Складено баланси енергії гідромашин ОРО200-В-100 та ОРО500-В-100. Відмічено, що розподіл втрат по елементам проточної частини нерівномірний: для ОРО200-В-100 найбільшу частину втрат складають втрати в робочому колесі (близько 56 %), для ОРО500-В-100 – втрати у підводі (близько 62 %). Описано основні положення визначення оптимального режиму роботи оборотної гідромашини. Запропоновано та досліджено модифікований підвід для тихохідної оборотної гідромашини ОРО500-В-100, щоб підвищити її енергетичні показники: краще узгоджені елементи ПЧ та гідравлічний ККД збільшився на 2 %.Thesis for granting the Degree of Candidate of Technical sciences in speciality 05.05.17 – Hydraulic machines and hydropneumatic units. – National Technical University "Kharkiv Polytechnic Institute", 2019. The tеhesis is devoted to the solution of the scientific and practical problem of improvement of the water passages of the high-pressure reversible hydraulic due to calculation and analysis their hydrodynamic characteristics. Based on the review of the trends in the development of hydropower engineering in Ukraine and given the role of high-pressure reversible hydraulic machines in the United Power System, it was noted that the designing a new flow parts is topical task. Advantages and disadvantages of the existing methods for research hydrodynamic processes in water passages of reversible hydraulic machines were identified after their analysis. The results of the calculation of the hydrodynamic characteristics of the elements of the water passages based on the method of averaged dimensionless parameters using the example of reversible hydraulic machines OPO200-B-100 and OPO500-B-100 were demonstrated. The mathematical model of the hydraulic machine working process based on a block-hierarchical approach was used to study the energy balance in the turbine and pump modes of hydraulic machines. The influence of the geometrical parameters of the elements of the water passage on the performance was determined: how the angle of flow in the spiral casing (cп ), the height of the wicket gate (b0 D) and the shape of the wicket gate profile influence the value of the coefficient resistance in the wicket gate. A numerical study of the three-dimensional flow of fluid in the water passage of high-pressure reversible hydraulic machines was carried out using the CFD software. This program allows determining the character of the flow and presenting the fields of distribution of velocity components, pressure and streamlines. The balances of energy were compiled: for the OPO200-B-100 in the turbine and pump operation modes, for the OPO500-B-100 in the turbine operation mode. It is noted that the distribution of losses on the elements of the water passage is not uniform: for the OPO200-B-100, the greatest part of the total losses are losses in the runner (about 56%), for OPO500-B-100 - losses in the inlet (about 62%). The main points for determining the optimal operating mode of the reversible hydraulic machine are described. The modified inlet for low-speed high-pressure hydraulic machine OPO500-B-100 was proposed and investigated to increase energy performance of hydraulic machine. The spiral casing was expanded, the number of stay vane blades and wicket gate blades were reduced to 16. As a result of the calculations of the modified inlet, the obtained results showed that the second variant made it possible to better align the elements of the water passage and the hydraulic efficiency increased by 2 %.
Частини книг з теми "Averaged dimensionless parameters"
1
T. Kajero, Olumayowa, Mukhtar Abdulkadir, Lokman Abdulkareem, and Barry James Azzopardi. "The Effect of Liquid Viscosity on the Rise Velocity of Taylor Bubbles in Small Diameter Bubble Column." In Vortex Dynamics Theories and Applications. IntechOpen, 2020. http://dx.doi.org/10.5772/intechopen.92754.
Повний текст джерелаАнотація:
The rise velocity of Taylor bubbles in small diameter bubble column was measured via cross-correlation between two planes of time-averaged void fraction data obtained from the electrical capacitance tomography (ECT). This was subsequently compared with the rise velocity obtained from the high-speed camera, manual time series analysis and likewise empirical models. The inertia, viscous and gravitational forces were identified as forces, which could influence the rise velocity. Fluid flow analysis was carried out using slug Reynolds number, Froude number and inverse dimensionless viscosity, which are important dimensionless parameters influencing the rise velocity of Taylor bubbles in different liquid viscosities, with the parameters being functions of the fluid properties and column diameter. It was found that the Froude number decreases with an increase in viscosity with a variation in flow as superficial gas velocity increases with reduction in rise velocity. A dominant effect of viscous and gravitational forces over inertia forces was obtained, which showed an agreement with Stokes law, where drag force is directly proportional to viscosity. Hence, the drag force increases as viscosity increases (5 < 100 < 1000 < 5000 mPa s), leading to a decrease in the rise velocity of Taylor bubbles. It was concluded that the rise velocity of Taylor bubbles decreases with an increase in liquid viscosity and, on the other hand, increases with an increase in superficial gas velocity.
Тези доповідей конференцій з теми "Averaged dimensionless parameters"
1
Fugal, Spencer R., Barton L. Smith, and Robert E. Spall. "A Numerical Study of 2-D Synthetic Jet Formation." In ASME 2004 Heat Transfer/Fluids Engineering Summer Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/ht-fed2004-56854.
Повний текст джерелаАнотація:
The formation of a two dimensional synthetic jet is studied numerically by solving the incompressible, unsteady, Reynolds-averaged, Navier-Stokes equations. Results for two exit geometries, a sharp exit and a rounded exit, and several dimensionless stroke lengths are compared. This study focuses on how the exit geometry and dimensionless stroke length change the following parameters: the power required to form the jet, the net momentum flux in the jet downstream of the exit, the formation threshold of the synthetic jet, and the location of the stagnation point during the suction portion of the cycle.
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Huang, Yuefeng, Zihan Zhang, Kun He, and Xin Yan. "Enhanced Film Cooling Effect Downstream of a Cylindrical Hole Using SDBD and DBD-VGs Plasma Actuations." In ASME Turbo Expo 2021: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/gt2021-59413.
Повний текст джерелаАнотація:
Abstract Effects of SDBD and DBD-VGs plasma actuations on film cooling performance of a plain wall were numerically investigated based on the RANS solutions and linearized body force model. With a user defined function (UDF), the plasma actuation forces were implemented into the momentum equations as the source terms in the commercial CFD solver ANSYS Fluent. With the experiment data and referenced numerical results, reliabilities of the linearized body force model and numerical methods were validated. At a range of dimensionless actuation strengths and frequencies, the film cooling effectiveness on the wall surface and flow structure development in the near-wall regions were analyzed and compared with the plasma-off case. The results show that both SDBD and DBD-VGs plasma actuations are beneficial for reducing the development of kidney vortex pair downstream of the cooling hole, thus significantly improving the film cooling effect on the wall surface. With SDBD plasma actuation, the streamwise velocity gradient in near-wall region is increased compared with the plasma-off case, resulting in delayed coolant flow lifting-off downstream of the cooling hole. However, with DBD-VGs plasma actuation, the development of anti-kidney vortex pair is intensified, which in turn weakens the development of kidney vortex pair and widens the coolant coverage on the wall surface along lateral direction. As the actuation strength and frequency increase, the film cooling effectiveness on the wall surface is enhanced along both streamwise and lateral directions. Compared with the plasma-off case, the area-averaged film cooling effectiveness for DBD-VGs plasma actuation case is increased by 331% at dimensionless actuation frequency of 2.5 and dimensionless actuation strength of 30, whereas for SDBD plasma actuation case the area-averaged film cooling effectiveness is only increased by 42.8% at dimensionless actuation frequency of 2.5 and dimensionless actuation strength of 60. With the same actuation parameters, compared against the SDBD case, a higher film cooling effectiveness is achieved on wall surface for the DBD-VGs plasma actuation case, and the coolant coverage along the lateral direction is significantly improved by DBD-VGs plasma actuation.
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Wu, Ruiqin, Wei Zhang, and Ming Hui Yao. "Analysis of Nonlinear Dynamics of a Rotor-Active Magnetic Bearing System With 16-Pole Legs." In ASME 2017 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/detc2017-67105.
Повний текст джерелаАнотація:
In this paper, we use the asymptotic perturbation method to analyze the nonlinear dynamics of a rotor-active magnetic bearing (AMB) system with 16-pole legs. The motion governing equation is derived by using classical Newton law. The resulting dimensionless equation of motion for the system is expressed as a two-degree-of-freedom system including the parametric excitation, quadratic and cubic nonlinearities. The asymptotic perturbation method is used to obtain the averaged equation when the primary resonance and 1/2 sub-harmonic resonance are taken into consideration. From the averaged equations obtained, numerical simulations are presented to investigate the modulation of vibration amplitudes of the rotor-AMB system. Based on a specific set of parameters, it is found that there exist the periodic, quasi-periodic and chaotic motions in the modulated amplitude of the rotor in the system.
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Liou, Tong-Miin, Chieh-Chu Chen, and Chun-Sheng Wang. "Effects of Attack Angle and Relative Thickness of Novel Wing-Shaped Turbulators on Turbulent Hydrothermal Performance in a Two-Pass Square Channel." In ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-14377.
Повний текст джерелаАнотація:
Abstract This work aims to combine the effects of the near wall and core flow disturbance by proposing novel wing-shaped tabulators. The new tabulators are fabricated with the fused deposition modeling (3D printing) technology. To explore their effects on detailed flow fields, local temperature distributions, and pressure drops in a two-pass square channel, Particle Image Velocimetry (PIV), Infrared Thermography (IR camera), and pressure transducer measurements are performed. The tabulator pitch, clearance, and truncation gap ratio based on the channel hydraulic diameter of 45.5 mm are respectively fixed at 0.7, 0.25 and 0.06. Varied parameters include tabulator attack angle (α = 10°, 15°, 20°, and 30°), maximum thickness to chord line ratio (t/C = 0.08, 0.13, 0.16, 0.20, and 0.23), and bulk Reynolds number (Re = 5,000–20,000). From the experimental results and flow parameters analyzed, the dimensionless spanwise-averaged mean transverse velocity and cross-sectionally averaged vorticity magnitude are identified to be the most relevant ones to spanwise-averaged local Nusselt number ratio in the first and second pass. Among all examined cases and previous data with Fanning friction factor ratio (f¯/fo) less than 50, the case with α = 20° and t/C = 0.20 attains the highest thermal performance factor and overall Nusselt number ratio (Nu¯/Nuo) up to 1.68 and 5.36, respectively. Furthermore, empirical correlations of Nu¯/Nuo and f¯/fo versus α, t/C, and Re are proposed.
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Jin, L. W., and K. C. Leong. "Effects of Displacement and Frequency of Oscillating Flow on Heat Transfer in a Porous Channel." In ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-61330.
Повний текст джерелаАнотація:
The development in modern electronics has resulted in rapid increases in power densities for electronic packages. Traditional cooling methods are not capable of removing such high heat fluxes. It is imperative to find new methods to cool high-speed electronic components. One of these methods is to implement a channel filled with a high conductivity porous medium. Many investigations have been conducted on the heat transfer of a channel filled with porous media. However, steady flow through a porous channel still yield a higher temperature difference along the flow direction. It is conceivable that oscillating flow through a porous channel will produce a more uniform temperature distribution due to the two thermal entrance regions of oscillating flow. Some researchers have investigated forced convective heat transfer in porous channels in oscillating flow with different kinds of porous media. Their results showed that the operating temperatures of electronic components can be reduced significantly when an oscillatory flow device is employed. However, research into the two critical factors of displacement and frequency for oscillating flow in a porous channel is very sparse. This paper presents the experimental results of an investigation into the effects of varying flow displacement and frequency on heat transfer enhancement in a porous channel subject to oscillating flow. A comparison was made between the heat transfer performance of oscillating flow through a plate channel without a porous medium and a channel filled with sintered metal foam. The maximum displacements of oscillating flow were varied from 52 to 68 mm and frequencies of oscillation ranged from 1 to 10 Hz. The characteristics of pressure drop, the effects of the dimensionless amplitude of displacement and dimensionless frequency of oscillating flow on heat transfer in porous channel were analyzed. The results revealed that heat transfer in oscillating flow is significantly enhanced by employing porous media in a plate channel. The cycle-averaged local Nusselt number increases with both kinetic Reynolds number Reω and the dimensionless amplitude of flow displacement A0. Based on the experimental data, a correlation equation of the length-averaged Nusselt number with the dimensionless parameters of Reω and A0 is obtained for a porous channel with L/Dh = 3. This correlation equation will be useful to determine heat transfer rates in oscillating flow through a porous channel for applications in electronics cooling.
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Barlow, Douglas N., and Yong W. Kim. "Effect of Surface Roughness on Local Heat Transfer and Film Cooling Effectiveness." In ASME 1995 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1995. http://dx.doi.org/10.1115/95-gt-014.
Повний текст джерелаАнотація:
An experimental investigation of film cooling on rough surfaces has been accomplished at a Reynolds number and dimensionless boundary layer momentum thickness found in current high performance first stage turbine vanes. A transient experimental method using thermochromic liquid crystals is employed to determine both local heat transfer coefficients and film cooling effectiveness values on planar rough surfaces. Two surface roughness configurations are investigated with a single row of cooling holes spaced three diameters apart and inclined 30° to the mainstream flow. The mainstream turbulence level at the point of film injection is 8.5% and the density ratio considered is approximately 1.0. The influence of roughness on the centerline film cooling effectiveness, laterally averaged film cooling effectiveness, laterally averaged heat transfer coefficients, as well as area averaged values are presented. It is found that the presence of roughness causes a decrease in the film cooling effectiveness over that of the smooth surface for the range of experimental parameters considered in this study. In addition, significant lateral smoothing in film cooling effectiveness distribution is observed for the rougher surfaces. Measured heat transfer coefficients on rough surfaces show a trend of monotonic increase with blowing ratio. However, such increase is not as great as that for the case of smooth surface.
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Murray, Daniel, and Jose´ L. Lage. "A 3D Numerical Simulation of a Cylindrical Towel Heater With Symmetric and Asymmetric Heating." In ASME/JSME 2011 8th Thermal Engineering Joint Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajtec2011-44638.
Повний текст джерелаАнотація:
In this study a cylindrical towel heater filled with air is simulated numerically in three-dimensions, with the cylinder being heated electrically from the side. The objective is to investigate the efficiency of the heating process as to maintain the towel at a certain temperature, higher than the ambient temperature (ambient temperature outside the heating cylinder), with the heating being symmetric or asymmetric. The process is modeled analytically assuming the towel as a homogeneous and isotropic porous medium, saturated with air, and enclosed by the cylinder. The cylinder wall is heated with a constant, symmetric or asymmetric heat flux, with the bottom surface assumed adiabatic and the top isothermal in equilibrium with the ambient air. The porous-continuum mass, momentum and energy equations for the natural convection inside the cylinder, derived through volume averaging the continuum equations with appropriate closure equations, are written in nondimensional form and solved numerically using the finite-volume method. A parametric study is then performed, after identifying suitable ranges for the parameters involved, to identify the effects of the several controlling parameters, namely the cylinder heating strength (the Rayleigh number), the towel permeability (the Darcy number), form coefficient (the dimensionless form coefficient), and thermal diffusivity (modified Prandtl number). The results, in terms of volume-averaged and surface-averaged temperatures and Nusselt numbers, indicate that the Darcy and Rayleigh numbers have a predominant effect on the natural convection process inside the cylinder, with the inertia coefficient and the modified Prandtl number having lesser influence on the results. For the asymmetric heating configuration, the resulting Nusselt number is higher while the volume-averaged temperature is lower, as compared to the symmetric heating. Hence, a symmetric heating is preferable if a high average towel temperature is the objective of the heater. If a more efficient heating process is sought, on the other hand, than the asymmetric option should be the best alternative.
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Campbell, Levi A., Michael J. Ellsworth, Madhusudan Iyengar, Robert Simons, and Richard Chu. "Experimental Investigation of the Heat Transfer Performance of Arrays of Round Jets With Sharp-Edged Orifices and Peripheral Effluent: Convective Behavior of Water on a Heated Silicon Surface." In ASME 2005 Summer Heat Transfer Conference collocated with the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems. ASMEDC, 2005. http://dx.doi.org/10.1115/ht2005-72397.
Повний текст джерелаАнотація:
In the present work, deionized water is impinged onto a heated silicon surface using square arrays of round jets. Various numbers of jets and jet diameters are used over a heated area of constant size with the orifice plate height above the heater held constant. In these experiments, the jet orifices are sharp-edged and the fluid exhaust direction is parallel to the heated surface and leaves the chip periphery through a manifold. The resulting temperature and flow data are presented in physical units as well as in groups of dimensionless parameters. A correlation is presented to reasonably predict the experimental results of this study. The techniques used for data reduction and for experimentation, including the construction of the test module, are given in detail, including a numerical conduction simulation based data reduction technique and uncertainty analysis. The results shown include flow rates ranging from 6.1 cc/s to 63.18 cc/s resulting in Reynolds numbers based on orifice diameter ranging from 141 to 6670. Jet diameters investigated in this study range from 377 μm to 1.01 mm, in square arrays of 16 to 324 orifices on an area of 18.52 mm × 18.59 mm. The resulting maximum spatially averaged effective heat transfer coefficient achieved is 7.94 W/cm2K, and the maximum spatially averaged Nusselt number based on jet diameter is 79.4.
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Cortés, Cristóbal, Inmaculada Arauzo, and Antonio Campo. "Dimensionless Parameters for the Optimization of Annular-Finned Tubes." In ASME 2000 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/imece2000-1280.
Повний текст джерелаАнотація:
Abstract This paper addresses the problem of optimizing an array of annular fins starting from an empirical fit of the average convection coefficient that recognizes the influence of the fin spacing. A dimensionless formulation is proposed to reduce the number of independent parameters to only four, being applicable to a rather generic situation. The formulation is illustrated with a parametric study encompassing the ranges of interest of the variables: Reynolds number, thermal conductivity ratio, volume constraint and fin spacing and thickness. Applied to the standard designs of annular-finned heat exchangers, the method predicts fully coherent points of optimum thermal performance. A sequence is suggested to integrate the optimization process within the design calculations of heat exchangers, and several graphs are presented which are suitable to this purpose. The method can be applied to the design and scaling calculations of annular-finned tube bundles for gas-liquid or gas-gas applications.
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Murakami, Toshihiro, Rei Takei, and Tomio Okawa. "Variation of Critical Heat Flux by Flow Oscillation in a Small Vertical Channel." In 17th International Conference on Nuclear Engineering. ASMEDC, 2009. http://dx.doi.org/10.1115/icone17-75147.
Повний текст джерелаАнотація:
The effect of sinusoidal oscillation of inlet mass flux on the critical heat flux (CHF) in forced convective boiling was investigated in experiment and numerical calculation. In the experiment, the test section was a small stainless steel round tube of 5 mm in inside diameter, filtrated and deionized tap water was used as a test fluid, and the flow direction was set to vertical upward. The heated length was 1,600 mm. Electric power supplied to a circulation pump was varied periodically to oscillate the inlet mass flux sinusoidally. Direct current was passed through the test section tube to heat it ohmically. The occurrence of critical heat flux condition was detected using the signal from the thermocouples that were spot-welded on the outer wall of the test section tube. In the present experimental conditions, it was expected that the critical heat flux condition was triggered by the dryout of liquid film in annular two-phase flow regime. The main experimental parameters were the time-averaged inlet mass flux and the amplitude and period of flow oscillation. The system pressure was also used as an important experimental parameter since a boiling water reactor is operated under high pressure condition. If the oscillation period is long enough, it is expected that the critical heat flux under the flow oscillation condition is close to that for the steady state when the flow rate is equal to the minimum flow rate in the oscillatory condition. On the other hand, the decrease of the critical heat flux would be mitigated if the oscillation period is shortened, since interaction would take place between the thin and thick film regions within a boiling channel. In accordance with this expectation, the critical heat flux measured under the flow oscillation condition was reduced with an increase in the oscillation period. It was demonstrated that the reduction of critical heat flux under flow oscillation condition can be correlated fairly well using the concept of dimensionless heated length. Numerical calculations using a one-dimensional three-fluid model were also carried. The calculated critical heat fluxes for flow oscillation conditions increased with increased value of dimensionless heated length, as in the present experiment.