Two parallel plane jets: Comparison of the performance of three turbulence models

1998 ◽  
Vol 212 (6) ◽  
pp. 379-391 ◽  
Author(s):  
J C S Lai ◽  
A Nasr
Keyword(s):  
Laser Doppler Anemometry ◽  
Turbulence Models ◽  
Domain Size ◽  
Flow Region ◽  
Quantitative Agreement ◽  
Parallel Plane ◽  
Computational Domain ◽  
Recirculation Flow ◽  
Plane Jets ◽  
Plane Jet

There have been many investigations in the literature to examine the performance of different turbulence models in predicting flow over backward-facing steps where the flow is bounded by solid boundaries. However, the evaluation of different turbulence models in predicting free shear layers with no solid boundaries, such as two parallel plane jets, is limited. In this paper, the velocity field of two parallel plane jets with a small nozzle separation ratio of s/ w = 4:25 determined by laser Doppler anemometry (LDA) is first presented. These experimental results are used to examine the performance of three turbulence models (i.e. k - ɛ, RNG k - ɛ and Reynolds stress) in predicting this flow field. The effects of computational domain size, grid resolution and different discretization schemes on the predictions are discussed. The existence of a recirculation flow region, a merging region and a combined region in the two parallel plane jet configuration has been predicted qualitatively by all three turbulence models. On the other hand, quantitative agreement between predictions and measurements varied by as much as 18 per cent for the merging length while the jet spread in the outer shear layer has been substantially under- predicted by all three models.

Numerical Investigation of Anisotropic Turbulence Effects Around a Film Cooled Turbine Vane

2002 ◽  
Author(s):  
Dieter E. Bohn ◽  
Christian Tu¨mmers
Keyword(s):  
Turbulence Model ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Flow Region ◽  
Main Flow ◽  
Experimental Investigations ◽  
Test Case ◽  
Similar Distribution ◽  
Computational Domain ◽  
Turbine Vane

In this paper the 3D flow around a turbine vane with showerhead cooling is simulated with the anisotropic cubic-eddy-viscosity k-ε turbulence model of Craft et. al. The results are analyzed in detail and compared to calculations performed with the isotropic algebraic turbulence model by Baldwin & Lomax and the isotropic Low-Reynolds k-ε-model of Launder et. al. for the same test case. The computational domain consists of the coolant supply (plenum), the ejection holes and the main flow region around the vane. Periodic boundary conditions have been used in the radial direction. Thus, endwall effects have been excluded. The numerical investigations focus on the influence of the anisotropic effects in the flow field. The flow conditions are taken from experimental investigations conducted by other authors and the results have been documented as a test case for numerical calculations of ejection flow phenomena. The results show a similar distribution of the predicted total pressure loss in the kidney vortex and downstream the ejection holes for the cubic-eddy viscosity model in comparison to the other turbulence models. Furthermore it is shown, that the influence of the cooling jets on the main flow, predicted by the two-equation models of Launder et. al. and Craft. et al., seems to be slightly higher compared to the algebraic model of Baldwin & Lomax.

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.

Analysis of Highly Swirled, Turbulent Flows in Dump Combustor With Exit Contraction

2005 ◽  
Author(s):  
Daniel A. Nickolaus ◽  
Clifford E. Smith
Keyword(s):  
Turbulent Flows ◽  
Recirculation Zone ◽  
Swirling Flow ◽  
Turbulence Models ◽  
Flow Patterns ◽  
Navier Stokes ◽  
Computational Domain ◽  
Recirculation Flow ◽  
Dump Combustor ◽  
Radial Profiles

Highly swirled flows are commonly used in gas turbine combustors to stabilize the flame and enhance fuel-air mixing. Experiments by D. G. Lilley, 1985 have shown that swirling flow patterns (i.e. recirculation zones) are dramatically impacted by a downstream contraction. For unconstricted swirling flow, a large, central recirculation zone is formed, while for constricted swirling flows, the recirculation zone can be annular in shape and high (positive) axial velocity is seen on the centerline of the combustor. Over the past 20 years, steady-state Reynolds Averaged Navier Stokes (RANS) solutions with various turbulence models have not been able to mimic the flowfield patterns for swirling flow with a downstream contraction. In this study, Large Eddy Simulation (LES) calculations were performed that correctly predicted the recirculation flow patterns for swirling flow with a downstream contraction. In addition, LES predicted radial profiles of swirl velocity agreed well with measurements, including the solid body vortex core on the centerline of the combustor. RANS produced inferior predictions. Two cases with 45° swirlers and a dump combustor with and without a downstream contraction were modeled. The LES predictions were compared with RANS predictions and Lilley’s measurements. The computational domain included flow through the swirl vanes, the combustor, and the contraction area. The unstructured, parallel CFD-ACE+ code was used, with the Localized Dynamic kinetic Energy Model (LDKM) for subgrid turbulence.

scholarly journals Optimising the computational domain size in CFD simulations of tall buildings

Heliyon ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. e06723
Author(s):  
Yousef Abu-Zidan ◽  
Priyan Mendis ◽  
Tharaka Gunawardena
Keyword(s):  
Tall Buildings ◽  
Domain Size ◽  
Computational Domain ◽  
Cfd Simulations

Multi-Objective Optimization of a Microturbine Compact Recuperator

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Diego Micheli ◽  
Valentino Pediroda ◽  
Stefano Pieri
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Numerical Procedure ◽  
Design Procedure ◽  
Domain Size ◽  
Multidisciplinary Optimization ◽  
Computational Domain ◽  
Surface Geometry ◽  
Multi Objective ◽  
Flux Boundary Conditions

An automatic approach for the multi-objective shape optimization of microgas turbine heat exchangers is presented. According to the concept of multidisciplinary optimization, the methodology integrates a CAD parametric model of the heat transfer surfaces, a three-dimensional meshing tool, and a CFD solver, all managed by a design optimization platform. The repetitive pattern of the surface geometry has been exploited to reduce the computational domain size, and the constant flux boundary conditions have been imposed to better suit the real operative conditions. A new approach that couples cold and warm fluids in a periodic unitary cell is introduced. The effectiveness of the numerical procedure was verified comparing the numerical results with available literature data. The optimization objectives are maximizing the heat transfer rate and minimizing both friction factor and heat transfer surface. The paper presents the results of the optimization of a 50kWMGT recuperator. The design procedure can be effectively extended and applied to any industrial heat exchanger application.

Evaluation of Different Turbulence Models Applied in Turbopump’s Hydraulic Turbine

2021 ◽  
Author(s):  
Daniel Ferreira Corrêa Barbosa ◽  
Daniel da Silva Tonon ◽  
Luiz Henrique Lindquist Whitacker ◽  
Jesuino Takachi Tomita ◽  
Cleverson Bringhenti
Keyword(s):  
Boundary Conditions ◽  
Turbulence Model ◽  
Rotor Blade ◽  
Space Shuttle ◽  
Turbulence Models ◽  
Tip Clearance ◽  
Test Facility ◽  
Speed Ratio ◽  
Computational Domain ◽  
Axial Turbine

Abstract The aim of this work is an evaluation of different turbulence models applied in Computational Fluid Dynamics (CFD) techniques in the turbomachinery area, in this case, in an axial turbine stage used in turbopump (TP) application. The tip clearance region was considered in this study because it has a high influence in turbomachinery performance. In this region, due to its geometry and the relative movement between the rotor row and casing, there are losses associated with vortices and secondary flow making the flowfield even more turbulent and complex. Moreover, the flow that leaks in the tip region does not participate in the energy transfer between the fluid and rotor blades, degradating the machine efficiency and performance. In this work, the usual flat tip rotor blade geometry was considered. The modeling of turbulent flow based on Reynolds Averaged Navier-Stokes (RANS) equations predicts the variation of turbine operational characteristics that is sufficient for the present turbomachine and flow analysis. Therefore, the appropriate choice of the turbulence model for the study of a given flow is essential to obtain adequate results using numerical approximations. This comparison become important due to the fact that there is no general turbulence model for all engineering applications that has fluid and flow. The turbomachine considered in the present work, is the first stage of the hydraulic axial turbine used in the Low Pressure Oxidizer Turbopump (LPOTP) of the Space Shuttle Main Engine (SSME), considering the 3.0% tip clearance configuration relative to rotor blade height. The turbulence models evaluated in this work were the SST (Shear Stress Transport), the k-ε Standard and the k-ε RNG. The computational domain was discretized in several control volumes based on unstructured mesh. All the simulations were performed using the commercial software developed by ANSYS, CFX v15.0 (ANSYS). All numerical settings and how the boundary conditions were imposed at different surfaces are explained in the work. The boundary conditions settings follow the same rule used in the test facility and needs some attention during the simulations to vary the Blade-Jet-Speed ratio parameter adequately. The results from numerical simulations, were synthesized and compared with the experimental data published by National Aeronautics and Space Administration (NASA), in which the turbine efficiency and its jet velocity parameter are analyzed for each turbulence model result. The work fluid considered in this work was water, the same fluid used in the NASA test facility.

Three-Dimensional Forced Convection in Plane Symmetric Sudden Expansion

2004 ◽  
Vol 126 (5) ◽  
pp. 836-839 ◽  
Author(s):  
J. H. Nie and ◽  
B. F. Armaly
Keyword(s):  
Nusselt Number ◽  
Forced Convection ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Flow Region ◽  
Outer Edge ◽  
Sudden Expansion ◽  
Recirculation Flow ◽  
Plane Symmetric ◽  
Laminar Forced Convection

Simulations of three-dimensional laminar forced convection in a plane symmetric sudden expansion are presented for Reynolds numbers where the flow is steady and symmetric. A swirling “jetlike” flow develops near the sidewalls in the separating shear layer, and its impingement on the stepped wall is responsible for the maximum that develops in the Nusselt number adjacent to the sidewalls and for the reverse flow that develops in that region. The maximum Nusselt number on the stepped wall is located inside the primary recirculation flow region and its location does not coincide with the jetlike flow impingement region. The results reveal that the location where the streamwise component of wall shear stress is zero on the stepped walls does not coincide with the outer edge of the primary recirculation flow region near the sidewalls.

Direct Numerical Simulations of a Transonic Tip Flow With Free-Stream Disturbances

2013 ◽  
Author(s):  
Andrew P. S. Wheeler ◽  
Richard D. Sandberg
Keyword(s):  
Heat Transfer ◽  
High Performance ◽  
Free Stream ◽  
Separation Bubble ◽  
Cross Flow ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Computational Domain ◽  
Free Stream Turbulence ◽  
Gap Height

In this paper we use direct numerical simulation to investigate the unsteady flow over a model turbine blade-tip at engine scale Reynolds and Mach numbers. The DNS is performed with a new in-house multi-block structured compressible Navier-Stokes solver purposely developed for exploiting high-performance computing systems. The particular case of a transonic tip flow is studied since previous work has suggested compressibility has an important influence on the turbulent nature of the separation bubble at the inlet to the gap and subsequent flow reattachment. The effects of free-stream turbulence, cross-flow and pressure-side boundary-layer on the tip flow aerodynamics and heat transfer are investigated. For ‘clean’ in-flow cases we find that even at engine scale Reynolds numbers the tip flow is intermittent in nature (neither laminar nor fully turbulent). The breakdown to turbulence occurs through the development of spanwise modes with wavelengths around 25% of the gap height. Cross-flows of 25% of the streamwise gap exit velocity are found to increase the stability of the tip flow, and to significantly reduce the turbulence production in the separation bubble. This is predicted through in-house linear stability analysis, and confirmed by the DNS. For the case when the inlet flow has free-stream turbulence, viscous dissipation and the rapid acceleration of the flow at the inlet to the tip-gap causes significant distortion of the vorticity field and reductions of turbulence intensity as the flow enters the tip gap. This means that only very high turbulence levels at the inlet to the computational domain significantly affect the tip heat transfer. The DNS results are compared with RANS predictions using the Spalart-Allmaras and k–ω SST turbulence models. The RANS and DNS predictions give similar qualitative features for the tip flow, but the size and shape of the inlet separation bubble and shock positions differ noticeably. The RANS predictions are particularly insensitive to free-stream turbulence.

Study of Wake Profiles of a Simplified Model of High Speed Train Using RANS and LES Turbulent Models

2014 ◽  
Vol 629 ◽  
pp. 426-430
Author(s):  
Sufiah Mohd Salleh ◽  
Mohamed Sukri Mat Ali ◽  
Sheikh Ahmad Zaki Shaikh Salim ◽  
Sallehuddin Muhamad ◽  
Muhammad Iyas Mahzan
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Sudden Change ◽  
Domain Size ◽  
Recirculation Region ◽  
Bluff Bodies ◽  
Computational Domain ◽  
High Speed Train ◽  
Free Shear Layer ◽  
Turbulent Models

Flow structure over bluff bodies is more complex in wake. The wake is characterized by the unsteady behavior of the flow, large scale turbulent structure and strong recirculation region. For the case of high speed train, wake can be observed at the gap between the coaches and also on the rear coach. Wakes formation of high speed train are generated by free shear layer that is originated from the flow separation due to the sudden change in geometry. RANS and LES turbulent models are used in this paper to stimulate the formation of wakes and behavior of the flow over a simplified high speed train model. This model consists of two coaches with the gap between them is 0.5D. A total of four simulations have been made to study the effect of computational domain size and grid resolution on wake profiles of a simplified high speed train. The result shows that the computational domain can be reduced by decreasing the ground distance to 1.5D without affecting the magnitude of the wake profile. Both RANS and LES can capture the formation of the wake, but LES requires further grid refinement as the results between the two grid resolutions are grid dependent.

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