Turbulent Forced Convection in a Plane Asymmetric Diffuser: Effect of Diffuser Angle

2007 ◽  
Author(s):  
H. Lan ◽  
B. F. Armaly ◽  
J. A. Drallmeier
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Forced Convection ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Separated Flow ◽  
Velocity Data ◽  
Measured Velocity ◽  
Flow And Heat Transfer ◽  
Diffuser Angle

Simulation of two-dimensional turbulent forced convection in a plane asymmetric diffuser is performed and the effect of diffuser angle on the flow and heat transfer is reported. This geometry is common in many heat exchanging devices and the convective heat transfer in it has not been examined. The flow field in this geometry, however, has received significant attention already and the results show that the υ2–f turbulence model provides a better comparison with measured velocity distributions than the k–ε turbulence models. This improvement in predictions is due to selecting different turbulent velocity scale and time scale for the eddy viscosity than what is used in conventional two-equation turbulence models. The results show that the diffuser angle influences significantly the flow field (separation and reattachment) and consequently, it must influence significantly the heat transfer. The υ2–f type turbulence models have been shown to provide good heat transfer results for separated flow, and for that reason a k-ε-ζ (or υ2–f type) turbulence model is used in this study. FLUENT 6.2.16 is used as the platform for these simulations and User Defined Functions (UDF) are developed to incorporate this turbulence model (which is not included in the commercial version of the FLUENT code at this time) into this CFD code. The UDF for the k-ε-ζ turbulence model is validated by comparisons with available measured velocity data in an asymmetric diffuser and with available measured heat transfer and velocity data in a backward facing step flow, and with heat transfer data for a normally-impinging jet flow with very good agreement between simulated and measured results.

Turbulent Forced Convection in a Plane Asymmetric Diffuser: Effect of Diffuser Angle

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
H. Lan ◽  
B. F. Armaly ◽  
J. A. Drallmeier
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Flow Region ◽  
Expansion Ratio ◽  
Benchmark Problems ◽  
Measured Velocity ◽  
Recirculation Flow ◽  
Diffuser Angle

A simulation of two-dimensional turbulent forced convection in a plane asymmetric diffuser with an expansion ratio of 4.7 is performed, and the effect of the diffuser angle on the flow and heat transfer is reported. This geometry is common in many heat exchanging devices, and the turbulent convective heat transfer in it has not been examined. The momentum transport in this geometry, however, has received significant attention already, and the studies show that the results from the υ2¯‐f type turbulence models provide better agreement with measured velocity distributions than that from the k‐ε or k‐ω turbulence models. In addition, the υ2¯‐f type turbulence models have been shown to provide good heat transfer results for separated and reattached flows. The k‐ε‐ζ (υ2¯‐f type) turbulence model is used in this study due to its improved numerical robustness, and the FLUENT-CFD code is used as the simulation platform. User defined functions for the k‐ε‐ζ turbulence model were developed and incorporated into the FLUENT-CFD code, and that process is validated by simulating the flow and the heat transfer in typical benchmark problems and comparing these results with available measurements. This new capability is used to study the effect of the diffuser angle on forced convection in an asymmetric diffuser, and the results show that the angle influences significantly both the flow and the thermal field. The increase in that angle increases the size of the recirculation flow region and enhances the rate of the heat transfer.

Steady RANS of Flow and Heat Transfer in a Smooth and Pin-Finned U-Duct With a Trapezoidal Cross Section

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Kenny S.-Y. Hu ◽  
Xingkai Chi ◽  
Tom I.-P. Shih ◽  
Minking Chyu ◽  
Michael Crawford
Keyword(s):  
Heat Transfer ◽  
Relative Error ◽  
Turbulence Models ◽  
Separated Flow ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Maximum Relative Error ◽  
Flow And Heat Transfer ◽  
Pin Fins ◽  
Turn Region

Steady Reynolds-averaged Navier--Stokes (RANS) simulations were performed to examine the ability of four turbulence models—realizable k–ε (k–ε), shear-stress transport (SST), Reynolds stress model with linear pressure strain (RSM-LPS), and stress-omega RSM (RSM-τω)—to predict the turbulent flow and heat transfer in a trapezoidal U-duct with and without a staggered array of pin fins. Results generated for the heat-transfer coefficient (HTC) were compared with experimental measurements. For the smooth U-duct, the maximum relative error in the averaged HTC in the up-leg is 2.5% for k–ε, SST, and RSM-τω and 9% for RSM-LPS. In the turn region, the maximum is 50% for k–ε and RSM-LPS, 14.5% for RSM-τω, and 29% for SST. In the down-leg, SST gave the best predictions and RSM-τω being a close second with maximum relative error less than 10%. The ability to predict the separated flow downstream of the turn dominated the performance of the models. For the U-duct with pin fins, SST and RSM-τω predicted the best, and k–ε predicted the least accurate HTCs. For k–ε, the maximum relative error is about 25%, whereas it is 15% for the SST and RSM-τω, and they occur in the turn. In the turn region, the staggered array of pin fins was found to behave like guide vanes in turning the flow. The pin fins also reduced the size of the separated region just after the turn.

Steady RANS of Flow and Heat Transfer in a Smooth and Pin-Finned U-Duct With a Trapezoidal Cross Section

2018 ◽  
Author(s):  
Kenny S.-Y. Hu ◽  
Xingkai Chi ◽  
Tom I-P. Shih ◽  
Minking Chyu ◽  
Michael Crawford
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Relative Error ◽  
Turbulence Models ◽  
Separated Flow ◽  
Maximum Relative Error ◽  
Trapezoidal Cross Section ◽  
Flow And Heat Transfer ◽  
Pin Fins ◽  
Turn Region

Steady RANS were performed to examine the ability of four turbulence models — realizable k-ε (k-ε), shear-stress transport (SST), Reynolds stress model with linear pressure strain (RSM-LPS), and stress-omega RSAM (RSM-τω) — to predict the turbulent flow and heat transfer in a U-duct with a trapezoidal cross section and with and without a staggered array of pin fins. Results generated for the heat-transfer coefficient (HTC) were compared with experimentally measured values. For the smooth U-duct, the maximum relative error in the averaged HTC in the up-leg is 2.5% for k-ε, SST, and RSM-τω and 9% for RSM-LPS. In the turn region, that maximum is 14.5% for RSM-τω, 29% for SST, and 50% for k-ε and RSM-LPS. In the down-leg, SST gave the best predictions and RSM-τω being a close second with maximum relative error less than 10%. The ability to predict the secondary flow in the turn region and the separated flow downstream of the turn dominated in how well the models predict the HTC. For the U-duct with pin fins, k-ε predicted the lowest and the least accurate HTCs, and SST and RSM-τω predicted the best. For k-ε, the maximum relative error in the averaged HTC is about 25%, whereas it is 15% for the SST and RSM-τω, and they occur in the turn. In the turn region, the staggered array of pin fins was found to behave like guide vanes in turning the flow. The pin fins also reduced the size of the separated region just after the turn.

Numerical Investigation of the Compressible Flat-Plate Turbulent Boundary Layer with Extended GAO-YONG Turbulence Model

2013 ◽  
Vol 444-445 ◽  
pp. 416-422
Author(s):  
Yang Yang Tang ◽  
Zhi Qiang Li ◽  
Yong Wang ◽  
Ya Chao Di ◽  
Huan Xu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Turbulence Model ◽  
Turbulence Models ◽  
Wall Region ◽  
Flow And Heat Transfer ◽  
Empirical Coefficients ◽  
Near Wall

The extended GAO-YONG turbulence model is used to simulate the flow and heat transfer of flat-plate turbulent boundary layer, and the results indicate that GAO-YONG turbulence model may well describe boundary layer flow and heat transfer from near-wall region to far outer area, without using any empirical coefficients and near-wall treatments, such as wall-function or modified low Reynolds number model, which are used widely in all RANS turbulence models.

Computations of Flow Field and Heat Transfer in a Stator Vane Passage Using the v2¯−f Turbulence Model

2005 ◽  
Vol 127 (3) ◽  
pp. 627-634 ◽  
Author(s):  
A. Sveningsson ◽  
L. Davidson
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Mean Flow ◽  
Stator Vane ◽  
Good Agreement

In this study three-dimensional simulations of a stator vane passage flow have been performed using the v2¯−f turbulence model. Both an in-house code (CALC-BFC) and the commercial software FLUENT are used. The main objective is to investigate the v2¯−f model’s ability to predict the secondary fluid motion in the passage and its influence on the heat transfer to the end walls between two stator vanes. Results of two versions of the v2¯−f model are presented and compared to detailed mean flow field, turbulence, and heat transfer measurements. The performance of the v2¯−f model is also compared with other eddy-viscosity-based turbulence models, including a version of the v2¯−f model, available in FLUENT. The importance of preventing unphysical growth of turbulence kinetic energy in stator vane flows, here by use of the realizability constraint, is illustrated. It is also shown that the v2¯−f model predictions of the vane passage flow agree well with experiments and that, among the eddy-viscosity closures investigated, the v2¯−f model, in general, performs the best. Good agreement between the two different implementations of the v2¯−f model (CALC-BFC and FLUENT) was obtained.

Computations of Flow Field and Heat Transfer in a Stator Vane Passage Using the v2–f Turbulence Model

2004 ◽  
Author(s):  
Andreas Sveningsson ◽  
Lars Davidson
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Fluid Motion ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Mean Flow ◽  
Stator Vane ◽  
Good Agreement

In this study three-dimensional simulations of a stator vane passage flow have been performed using the v2–f turbulence model. Both an in-house code (CALC-BFC) and the commercial software Fluent are used. The main objective is to investigate the v2–f model’s ability to predict the secondary fluid motion in the passage and its influence on the heat transfer to the endwalls between two stator vanes. Results of two versions of the v2–f model are presented and compared with detailed mean flow field, turbulence and heat transfer measurements. The performance of the v2–f model is also compared with other eddy-viscosity based turbulence models, including a version of the v2–f model, available in Fluent. The importance of preventing unphysical growth of turbulence kinetic energy in stator vane flows, here by use of the realizability constraint, is illustrated. It is also shown that the v2–f model predictions of the vane passage flow agree well with experiments and that, amongst the eddy-viscosity closures investigated, the v2–f model in general performs the best. Good agreement between the two different implementations of the v2–f model (CALC-BFC and Fluent) was obtained.

Fundamental Issues and Recent Advancements in Analysis of Aircraft Brake Natural Convective Cooling

1998 ◽  
Vol 120 (4) ◽  
pp. 840-857 ◽  
Author(s):  
M. P. Dyko ◽  
K. Vafai
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flow Field ◽  
Three Dimensional ◽  
Convective Cooling ◽  
Cooling Flow ◽  
Physical Mechanisms ◽  
Braking System ◽  
Flow And Heat Transfer ◽  
Convection Cooling

A heightened awareness of the importance of natural convective cooling as a driving factor in design and thermal management of aircraft braking systems has emerged in recent years. As a result, increased attention is being devoted to understanding the buoyancy-driven flow and heat transfer occurring within the complex air passageways formed by the wheel and brake components, including the interaction of the internal and external flow fields. Through application of contemporary computational methods in conjunction with thorough experimentation, robust numerical simulations of these three-dimensional processes have been developed and validated. This has provided insight into the fundamental physical mechanisms underlying the flow and yielded the tools necessary for efficient optimization of the cooling process to improve overall thermal performance. In the present work, a brief overview of aircraft brake thermal considerations and formulation of the convection cooling problem are provided. This is followed by a review of studies of natural convection within closed and open-ended annuli and the closely related investigation of inboard and outboard subdomains of the braking system. Relevant studies of natural convection in open rectangular cavities are also discussed. Both experimental and numerical results obtained to date are addressed, with emphasis given to the characteristics of the flow field and the effects of changes in geometric parameters on flow and heat transfer. Findings of a concurrent numerical and experimental investigation of natural convection within the wheel and brake assembly are presented. These results provide, for the first time, a description of the three-dimensional aircraft braking system cooling flow field.

Sign in / Sign up

Export Citation Format

Share Document