Modeling a Discrete Interaction Jets/Wall Flow. Effect of Curvature

2011 ◽  
Vol 274 ◽  
pp. 71-80
Author(s):  
Amar Berkache ◽  
Rabah Dizene
Keyword(s):  
Flat Plate ◽  
Turbine Blades ◽  
Cross Flow ◽  
Turbulence Models ◽  
Curvature Effects ◽  
Wall Boundary Layer ◽  
Sst Model ◽  
Wall Flow ◽  
Discrete Interaction ◽  
Wall Interaction

A numerical simulation is used to evaluate the curvature effects of the wall on features of the interaction between discrete jets and cross flow, and therefore on the efficiency of the cooling. The injection is realized in a turbulent limit layer through only one row of openings. Our study was especially based on the SST model that is efficient in the capture of the phenomena near and in the wall. Three turbulence models are used; the k-, the RSM and the SST on a flat plate crossed by throw in order to identify which of these models are more capable to capture the near wall interaction phenomena. Discrete jets are arranged across a surface exposed to a wall boundary layer of parallel compressible stream, as occurs in certain discrete-hole cooling systems for turbine blades. Comparisons of the results of this study are presented in the case of a flat plate crossed by throw inclined of 45° with a rate injection Ra=0.6. These results compared to experimental data proved the aptitude of the SST model, in relation to the other models in this case of problems. Applied for a NACA0012 profile, this model (SST) revealed us the distinct difference of features of the interaction in relation to the flat plate.

Performance of Two-Equation Turbulence Models for Flat Plate Flows With Leading Edge Bubbles

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
S. Collie ◽  
M. Gerritsen ◽  
P. Jackson
Keyword(s):  
Flat Plate ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Leading Edge ◽  
Test Case ◽  
Sst Model ◽  
Two Dimensional Flow ◽  
Experimental Values ◽  
University Of Bristol ◽  
Sharp Leading Edge

This paper investigates the performance of the popular k-ω and SST turbulence models for the two-dimensional flow past the flat plate at shallow angles of incidence. Particular interest is paid to the leading edge bubble that forms as the flow separates from the sharp leading edge. This type of leading edge bubble is most commonly found in flows past thin airfoils, such as turbine blades, membrane wings, and yacht sails. Validation is carried out through a comparison to wind tunnel results compiled by Crompton (2001, “The Thin Aerofoil Leading Edge Bubble,” Ph.D. thesis, University of Bristol). This flow problem presents a new and demanding test case for turbulence models. The models were found to capture the leading edge bubble well with the Shear-Stress Transport (SST) model predicting the reattachment length within 7% of the experimental values. Downstream of reattachment both models predicted a slower boundary layer recovery than the experimental results. Overall, despite their simplicity, these two-equation models do a surprisingly good job for this demanding test case.

Computational Fluid Dynamics Evaluation of Heat Transfer Correlations for Sodium Flows in a Heat Exchanger

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Seok-Ki Choi ◽  
Seong-O Kim ◽  
Hoon-Ki Choi
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Turbulence Model ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Cross Flow ◽  
Turbulence Models ◽  
Parallel Flow ◽  
Sst Model ◽  
Heat Transfer Correlations

A numerical study for the evaluation of heat transfer correlations for sodium flows in a heat exchanger of a fast breeder nuclear reactor is performed. Three different types of flows such as parallel flow, cross flow, and two inclined flows are considered. Calculations are performed for these three typical flows in a heat exchanger changing turbulence models. The tested turbulence models are the shear stress transport (SST) model and the SSG-Reynolds stress turbulence model by Speziale, Sarkar, and Gaski (1991, “Modelling the Pressure-Strain Correlation of Turbulence: An Invariant Dynamical System Approach,” J. Fluid Mech., 227, pp. 245–272). The computational model for parallel flow is a flow past tubes inside a circular cylinder and those for the cross flow and inclined flows are flows past the perpendicular and inclined tube banks enclosed by a rectangular duct. The computational results show that the SST model produces the most reliable results that can distinguish the best heat transfer correlation from other correlations for the three different flows. It was also shown that the SSG-RSTM high-Reynolds number turbulence model does not deal with the low-Prandtl number effect properly when the Peclet number is small. According to the present calculations for a parallel flow, all the old correlations do not match with the present numerical solutions and a new correlation is proposed. The correlations by Dwyer (1966, “Recent Developments in Liquid-Metal Heat Transfer,” At. Energy Rev., 4, pp. 3–92) for a cross flow and its modified correlation that takes into account of flow inclination for inclined flows work best and are accurate enough to be used for the design of the heat exchanger.

Investigation of the Performance of Turbulence Models With Respect to High Flow Curvature in Centrifugal Compressors

2015 ◽  
Vol 138 (5) ◽  
Author(s):  
Shady Ali ◽  
Kevin J. Elliott ◽  
Eric Savory ◽  
Chao Zhang ◽  
Robert J. Martinuzzi ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Field Analysis ◽  
Mean Flow ◽  
Production Term ◽  
Curvature Effects ◽  
Sst Model ◽  
Aero Engine ◽  
Compressor Impeller

The goal of this research is to evaluate the performance of three turbulence models with respect to flow with high curvature in a centrifugal compressor stage designed for an aero-engine. The effectiveness of the curvature correction terms in the two-equation turbulence models is the main focus of this study, as implemented in the curvature-corrected shear stress transport (SST-CC) model of Smirnov and Menter. The SST-CC model uses a production multiplier in the k and ω equations. SST-CC results were compared against the SST model and previous simulations by Bourgeois et al. (2011, “Assessment of Turbulence Model Predictions for an Aero-Engine Centrifugal Compressor,” ASME J. Turbomach., 133(1), pp. 1–15) using the Reynolds stress model (RSM–SSG) for stage performance characteristics, experimental velocity profiles at the impeller–diffuser interface, and velocity contours at the diffuser exit. The production multiplier was investigated in the compressor impeller. The comparisons showed that the SST-CC model better predicted the choke region in the pressure characteristic and efficiency characteristic, whereas the SST model better predicted the stall region. However, both models predicted a similar mean flow velocity field. Analysis of the production multiplier demonstrated that the term provided the expected effects near the walls of the convex and concave surfaces. However, away from the walls where turbulent production term was insignificant, the production multiplier showed abnormal predictions. The rotation effects were found to be weaker than the curvature effects near the impeller trailing edge of the current compressor.

A Validation of CFD Methods on Predicting Valve Performance Parameters

2018 ◽  
Author(s):  
Yu Duan ◽  
Matthew D. Eaton ◽  
Michael J. Bluck ◽  
Christopher Jackson
Keyword(s):  
Turbulence Models ◽  
Acceptable Error ◽  
Cfd Models ◽  
Physical Measurements ◽  
Viscosity Models ◽  
Sst Model ◽  
Mesh Resolution ◽  
Wall Flow ◽  
Poppet Valves ◽  
Near Wall

The influence of mesh resolution, the abilities of various eddy viscosity models, and near wall flow treatments on predicting the flow coefficients of poppet valves, operating in water are investigated in this paper. The computational fluid dynamics (CFD) models are solved using STAR-CCM+ 12.04. Grid-convergence is studied first, followed by quantitative assessments of the ability of standard k-ε model, realizable k-ε model, EB k-ε model, Lag EB k-ε model, V2F model and k-ω-sst model, and different wall treatments, such as high y+ wall treatment, two-layer wall treatment and all y+ wall treatment, embedded in the solver. The flow discharge coefficient (Cq) of poppet valves predicted by CFD models are compared to physical measurements. It was demonstrated in the study that grid resolutions normal to the wall and mesh quality are key factors. Advanced near wall flow treatments produce similar or worse predictions when using the standard k-ε model, and the effects of the near wall flow treatments are marginal for the realizable k-ε model. The ability of turbulence models varies greatly in predicting flow in different valves and lift levels. The realizable k-ε model is the optimal option for the considered valve flows giving an acceptable error within ±5%.

scholarly journals LES and RANS Analysis of the End-Wall Flow in a Linear LPT Cascade With Variable Inlet Conditions: Part II — Loss Generation

2018 ◽  
Author(s):  
Michele Marconcini ◽  
Roberto Pacciani ◽  
Andrea Arnone ◽  
Vittorio Michelassi ◽  
Richard Pichler ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Companion Paper ◽  
Wall Boundary Layer ◽  
Wall Flow ◽  
Inlet Conditions ◽  
End Wall ◽  
The Impact

In low-pressure-turbines (LPT) at design point around 60–70% of losses are generated in the blade boundary layers far from end-walls, while the remaining 30%–40% is controlled by the interaction of the blade profile with the end-wall boundary layer. Increasing attention is devoted to these flow regions in industrial design processes. Experimental techniques have shed light on the mechanism that controls the growth of the secondary vortices, and scale-resolving CFD have provided a detailed insight into the vorticity generation. Along these lines, this paper discusses the end-wall flow characteristics of the T106 profile with parallel end-walls at realistic LPT conditions, as described in the experimental setup of Duden and Fottner (1997) “Influence of Taper, Reynolds Number and Mach Number on the Secondary Flow Field of a Highly Loaded Turbine Cascade”, P. I. Mech. Eng. A-J. Pow., 211 (4), pp.309–320. The simulations target first the same inlet conditions as documented in the experiments, and determines the impact of the incoming boundary layer thickness by running additional cases with modified incoming boundary layers. Calculations are carried out by both RANS, due to its continuing role as the design verification workhorse, and highly-resolved LES. Part II of the paper focuses on the loss generation associated with the secondary end-wall vortices. Entropy generation and the consequent stagnation pressure losses are analyzed following the aerodynamic investigation carried out in the companion paper. The ability of classical turbulence models generally used in RANS to discern the loss contributions of the different vortical structures is discussed in detail and the attainable degree of accuracy is scrutinized with the help of LES and the available test data. The purpose is to identify the flow features that require further modelling efforts in order to improve RANS/URANS approaches and make them able to support the design of the next generation of LPTs.

An Assessment of Turbulence Models in Simulating a Synthetic Jet

2013 ◽  
Vol 465-466 ◽  
pp. 603-607
Author(s):  
Greg G. Gomang ◽  
Ann Lee
Keyword(s):  
Experimental Data ◽  
Shear Stress ◽  
Numerical Study ◽  
Cross Flow ◽  
Turbulence Models ◽  
Synthetic Jet ◽  
Shear Stress Transport ◽  
Sst Model ◽  
Realistic Prediction ◽  
Good Agreement

This paper presents a two-dimensional numerical study on the interaction of synthetic jet and the cross flow inside a microchannel. Three different turbulence models namely the standard k-, Shear Stress Transport (SST) and Scale Adaptive Simulation Shear Stress Transport (SAS SST) were tested for their ability to predict the flow structure generated by a synthetic jet. The results are validated against existing experimental data. The SAS SST model was found to give the most realistic prediction of the fluid flow based on the good agreement with experimental data.

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