Study of Turbulent Variable Density Jets With Different Asymmetric Geometries

Volume 1 ◽  
2004 ◽  
Author(s):  
Bachir Imine ◽  
Miloud Abidat ◽  
Omar Imine ◽  
Hichem Gazzah ◽  
Iskender Go¨kalp
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Turbulent Kinetic Energy ◽  
Comparative Studies ◽  
Longitudinal Velocity ◽  
Turbulent Jets ◽  
Reynolds Stress Model ◽  
Variable Density ◽  
Stress Model ◽  
Density Ratios

In the present study, the effects of inlet jet geometry on the process of mixture with variable density have been investigated numerically. Three density ratios were considered, namely 1.0, 1.8 and 0.66 for Air-air, CH4-Air and CO2-Air mixtures respectively. The jets are produced through rectangular, elliptic and triangular tubes with aspect ratio 1.33. A second-order Reynolds stress model (RSM) is used to investigate variable density effects in asymmetric turbulent jets. Comparative studies are presented in the case of the calculations of the average variables such as the longitudinal velocity, species and the turbulent kinetic energy. The results obtained show that the asymmetric geometry noticeably enhances mixture in comparison with the axisymmetric case. Typical phenomenon of 3D jets are observed.

Measurements and Predictions of a Highly Turbulent Flowfield in a Turbine Vane Passage

2000 ◽  
Vol 122 (4) ◽  
pp. 666-676 ◽  
Author(s):  
R. W. Radomsky ◽  
K. A. Thole
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flow ◽  
Gas Turbine ◽  
Turbulent Kinetic Energy ◽  
Reynolds Stress ◽  
Complex Geometry ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Mean Flow

As highly turbulent flow passes through downstream airfoil passages in a gas turbine engine, it is subjected to a complex geometry designed to accelerate and turn the flow. This acceleration and streamline curvature subject the turbulent flow to high mean flow strains. This paper presents both experimental measurements and computational predictions for highly turbulent flow as it progresses through a passage of a gas turbine stator vane. Three-component velocity fields at the vane midspan were measured for inlet turbulence levels of 0.6%, 10%, and 19.5%. The turbulent kinetic energy increased through the passage by 130% for the 10% inlet turbulence and, because the dissipation rate was higher for the 19.5% inlet turbulence, the turbulent kinetic energy increased by only 31%. With a mean flow acceleration of five through the passage, the exiting local turbulence levels were 3% and 6% for the respective 10% and 19.5% inlet turbulence levels. Computational RANS predictions were compared with the measurements using four different turbulence models including the k-ε, Renormalization Group (RNG) k-ε, realizable k-ε, and Reynolds stress model. The results indicate that the predictions using the Reynolds stress model most closely agreed with the measurements as compared with the other turbulence models with better agreement for the 10% case than the 19.5% case. [S0098-2202(00)00804-X]

PIV Investigation of Separated and Reattached Turbulent Flows Over Ribs of Various Aspect Ratio

2014 ◽  
Author(s):  
Kathryn M. Atamanchuk ◽  
Mark F. Tachie
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Turbulent Kinetic Energy ◽  
Turbulent Flows ◽  
Reynolds Shear Stress ◽  
Separated Flow ◽  
Particle Image Velocimetry System ◽  
Shear Stresses ◽  
Mean Velocity ◽  
Freestream Velocity

An experimental study is undertaken to investigate the features of separated and reattached flow over surface mounted traverse ribs of varying aspect ratio (1:1, 1:2, and 1:4) in a recirculating open channel turbulent flow. A particle image velocimetry system was used to conduct the velocity measurements. Upstream conditions were kept consistent among all three test cases. The reattachment length of the separated flow was found to decrease as rib aspect ratio increased, primarily as a result of a secondary separation reattachment formation on the ribs of increased aspect ratio. Contour plots of mean velocities, turbulence intensities, turbulent kinetic energy and Reynolds shear stresses, as well as one-dimensional profiles of streamwise mean velocity, turbulent kinetic energy and Reynolds shear stress in the recirculation and reattachment region are presented and discussed. The results show that maximum wall-normal mean velocities are approximately 40% of the approach freestream velocity. The results also indicate that the turbulence levels downstream of the block tend to decrease as the rib aspect ratio increases.

Development of Turbulent Quantities Inside an Axial Turbine Vane

2021 ◽  
Author(s):  
Stephan Behre ◽  
Dragan Kožulović ◽  
Christian Hösgen ◽  
Peter Jeschke
Keyword(s):  
Experimental Data ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Axial Flow ◽  
Turbulent Energy ◽  
Reynolds Stress Model ◽  
Cfd Simulations ◽  
Velocity Gradients ◽  
Extensive Field

Abstract The paper presents experimental and numerical investigations of the three components of turbulent kinetic energy and its development upstream and downstream of the first vane of 1.5 stage axial flow turbine. The experimental data has been recorded using a miniature hot wire probe, equipped with three 9μm platinized tungsten wires, allowing the determination of the kinetic energy in all three spatial directions. By means of turbulent grids, a total of three different inlet turbulence levels, varying from 0.4 to 4.5%, was created. Extensive field traverses up- and downstream of the first stator have been conducted, covering more than one stator pitch and including both the free stream and the wake. For one inlet condition, a total of three axial positions between the stator and the rotor have been measured to evaluate the development of the composition of the turbulence. The type of turbulence is visualized by making use of the barycentric color map. Detailed investigations of all three fluctuation components reveal that, depending on the anisotropy level and the distribution of energy along the three spatial directions at the stator’s inlet, the velocity gradients within the first stator either promote a production or destruction of turbulent kinetic energy. As a consequence, the distribution of turbulent energy along the three spatial directions is at the stator’s outlet almost identical for the three configurations. Finally, the measurements with focus on the turbulence composition are compared to unsteady CFD simulations using, the, in industrial application, most commonly applied k-w turbulence model. In addition, an Explicit Algebraic Reynolds Stress Model (EARSM) is also applied and compared to numerical and experimental data. However, the paper is focused on the interpretation of the experimental data.

scholarly journals INFLUENCE OF ASPECT RATIO IN THE TURBULENT CONVECTION IN CAVITIES

2013 ◽  
Vol 12 (2) ◽  
pp. 73
Author(s):  
R. M. Guimarães ◽  
V. C. Mariani ◽  
K. C. Mendonça
Keyword(s):  
Fluid Dynamics ◽  
Aspect Ratio ◽  
Turbulent Flow ◽  
Numerical Investigation ◽  
Turbulence Model ◽  
Reynolds Stress Model ◽  
Turbulent Convection ◽  
Air Distribution ◽  
Stress Model ◽  
Rectangular Room

The purpose of this study is to know the air distribution in a conditioned room, through the numerical investigation of the influence of aspect ratio in the thermal and fluid dynamics behavior of a turbulent flow. To achieve that objective, some simulations were done of the flow inside a rectangular room, where the air enters through an opening in the top of one wall and leaves the room through an opening in the bottom of the opposite wall. The Reynolds mean equations are used, with the turbulence model RSM BSL (Reynolds Stress Model - Baseline) to solve four cases, with different geometries. It was concluded that, in general, the turbulence model used in this work is capable to predict quite well the fluid dynamics behavior of the flow, which is influenced by the room length, but not by its width.

Complete self-preservation on the axis of a turbulent round jet

2016 ◽  
Vol 790 ◽  
pp. 57-70 ◽  
Author(s):  
L. Djenidi ◽  
R. A. Antonia ◽  
N. Lefeuvre ◽  
J. Lemay
Keyword(s):  
Reynolds Number ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Energy Budget ◽  
Dissipation Rate ◽  
Longitudinal Velocity ◽  
Order Structure ◽  
Mean Velocity ◽  
Round Jet ◽  
The Mean

Self-preservation (SP) solutions on the axis of a turbulent round jet are derived for the transport equation of the second-order structure function of the turbulent kinetic energy ($k$), which may be interpreted as a scale-by-scale (s.b.s.) energy budget. The analysis shows that the mean turbulent energy dissipation rate, $\overline{{\it\epsilon}}$, evolves like $x^{-4}$ ($x$ is the streamwise direction). It is important to stress that this derivation does not use the constancy of the non-dimensional dissipation rate parameter $C_{{\it\epsilon}}=\overline{{\it\epsilon}}u^{\prime 3}/L_{u}$ ($L_{u}$ and $u^{\prime }$ are the integral length scale and root mean square of the longitudinal velocity fluctuation respectively). We show, in fact, that the constancy of $C_{{\it\epsilon}}$ is simply a consequence of complete SP (i.e. SP at all scales of motion). The significance of the analysis relates to the fact that the SP requirements for the mean velocity and mean turbulent kinetic energy (i.e. $U\sim x^{-1}$ and $k\sim x^{-2}$ respectively) are derived without invoking the transport equations for $U$ and $k$. Experimental hot-wire data along the axis of a turbulent round jet show that, after a transient downstream distance which increases with Reynolds number, the turbulence statistics comply with complete SP. For example, the measured $\overline{{\it\epsilon}}$ agrees well with the SP prediction, i.e. $\overline{{\it\epsilon}}\sim x^{-4}$, while the Taylor microscale Reynolds number $Re_{{\it\lambda}}$ remains constant. The analytical expression for the prefactor $A_{{\it\epsilon}}$ for $\overline{{\it\epsilon}}\sim (x-x_{o})^{-4}$ (where $x_{o}$ is a virtual origin), first developed by Thiesset et al. (J. Fluid Mech., vol. 748, 2014, R2) and rederived here solely from the SP analysis of the s.b.s. energy budget, is validated and provides a relatively simple and accurate method for estimating $\overline{{\it\epsilon}}$ along the axis of a turbulent round jet.

scholarly journals Numerical investigation of mixture generation due to different inlet and outlet positions

2019 ◽  
Vol 15 (2) ◽  
pp. 308-317
Author(s):  
Hussain Saad Abd ◽  
Abdulmunem R Abdulmunem ◽  
Mohammed Hassan Jabal
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Dead Zone ◽  
Sudden Change ◽  
Flow Characteristics ◽  
Reynolds Stress Model ◽  
Accurate Solution ◽  
Flow Properties ◽  
Navier Stokes Equation ◽  
Rate Of Dissipation

Abstract A numerical simulation is a method carried out to study the flow characteristics of compressible fluid through different channels. Two approaches using air as a working substance were used to study the flow characteristics. In the first approach, two inlets and one outlet horizontally in the x direction was depended on to generate different flow characteristics; the flow properties were calculated along the diagonal line inside the channel. In the second approach, one inlet and outlet horizontally with sudden change in the area of the channel was employed. In this research, the flow properties were calculated along the center line inside the channel and the flow fields have been investigated. A non-linear k-Є model is employed to solve the flow characteristics by using the finite difference method with a curvilinear coordinate system near the dead zone and the k-Є and Reynolds stress model area semi-empirical model based on modeling of the equations of transport that contain the dissipation rate (ε) as well as turbulent kinetic energy (k). The derivation of turbulent kinetic energy and its rate of dissipation derived from the Navier–Stokes equation. In this work, the simulation outcomes of the proposed k-ε turbulence model indicated a good compatibility with published correlations. In order to get an accurate solution, the value of 10–8 for the maximal normalized equation residual was considered to be the convergence between computation and steady solution. The model applied for flow velocity 30 m/s and the obtained results presented as curves, surface and contours for velocities turbulent kinetic energy, rate of dissipation of turbulent kinetic energy and vortices. The builder model can be utilized for academic purposes since it is widely used for many physical and engineering applications.

The mixing region in freely decaying variable-density turbulence

2015 ◽  
Vol 772 ◽  
pp. 386-426 ◽  
Author(s):  
Pooya Movahed ◽  
Eric Johnsen
Keyword(s):  
Kinetic Energy ◽  
Density Gradient ◽  
Kinematic Viscosity ◽  
Density Ratio ◽  
Variable Density ◽  
Unit Mass ◽  
Material Interface ◽  
Variable Density Turbulence ◽  
Set Up ◽  
Density Ratios

A novel set-up is proposed to numerically study turbulent multimaterial mixing, starting from an unperturbed material interface between a light and a heavy fluid. We conduct direct numerical simulation (DNS) to better understand the role of density gradient alone on the turbulence, specifically with regard to the mixing region dynamics and anisotropy across scales. Freely decaying isotropic turbulent fields of different densities but identical kinematic viscosities are juxtaposed. The rationale for this strategy is that conventional turbulence scalings are based on kinetic energy per unit mass and kinematic viscosity. Thus, by matching the initial kinematics (root-mean-square velocity) and the dissipation (kinematic viscosity), the turbulence (kinetic energy per unit mass) decays at the same rate in both fluids. With this set-up, the effect of the density gradient alone on the turbulence can be considered, independently from other contributions (e.g. mismatch in kinetic energy per unit mass, acceleration field, etc.). We examine the mixing region dynamics at large and small scales for different density ratios and Reynolds numbers. After an initial transient, we observe a self-similar growth of the mixing region, which we explain via theoretical arguments verified by the DNS results. Inside the mixing region, the momentum of the heavier eddies causes the mean interface location to shift toward the light fluid. A higher density ratio leads to a wider, less molecularly mixed mixing region. Although anisotropy is evident at the large scales, the dissipation scales remain essentially isotropic, even at the highest density ratio under consideration (12:1). The intermittency of the velocity field exhibits isotropy, while the mass fraction field is more intermittent in the direction of the density gradient.

RECIRCULATION OF CONFINED VARIABLE DENSITY TURBULENT JETS

2004 ◽  
Vol 27 (4) ◽  
pp. 279-294
Author(s):  
A. Benaissa ◽  
M.F. Bardon ◽  
J.E.D. Gauthier ◽  
F. Anselmet ◽  
E. Ruffïn
Keyword(s):  
Experimental Data ◽  
Turbulent Flow ◽  
Flow Pattern ◽  
Initial Conditions ◽  
Numerical Study ◽  
Turbulent Jets ◽  
Variable Density ◽  
Confined Jets ◽  
Recirculating Flow ◽  
Density Ratios

An investigation of recirculating characteristics of circular turbulent confined jets with large density variations is presented. This numerical study aims at testing analytical predictions associated with the Craya-Curtet number. It investigates also its effect on the dynamic field and recirculation. It appears that for different density (He-air, CO2-air) and geometry ratios, the non-isothermal Craya-Curtet number [1] is not sufficient to describe the flow pattern or predict its recirculation. Depending on the momentum, aspect and density ratios of the flow, the centre of the recirculating flow (the eye) tends to reach the initial (non-self-preserving) region of the jet and influences the development of the jet. As a consequence, predictions are not in agreement with theory. The reason is that initial conditions do not satisfy the hypothesis used in the prediction of recirculation theory. Calculations are performed in three configurations: CO2, air and He. These configurations are fully developed pipe jets evolving in an air secondary turbulent flow. Validations are performed using experimental data [2] obtained in similar configurations for the three gases.

Analysis of Impinging and Countercurrent Stagnating Flows by Reynolds Stress Model

2002 ◽  
Vol 124 (3) ◽  
pp. 706-718 ◽  
Author(s):  
Yong H. Im ◽  
Kang Y. Huh ◽  
Kwang-Yong Kim
Keyword(s):  
Numerical Simulation ◽  
Kinetic Energy ◽  
Turbulent Flows ◽  
Reynolds Stress ◽  
Dissipation Rate ◽  
Flow Characteristics ◽  
Turbulence Models ◽  
Reynolds Stress Model ◽  
Stress Model ◽  
Stagnation Region

Numerical simulation is performed for stagnating turbulent flows of impinging and countercurrent jets by the Reynolds stress model (RSM). Results are compared with those of the k−ε model and available data to assess the flow characteristics and turbulence models. Three variants of the RSM tested are those of Gibson and Launder (GL), Craft and Launder (GL-CL) and Speziale, Sarkar and Gatski (SSG). As is well known, the k−ε model significantly overestimates turbulent kinetic energy near the wall. Although the RSM is superior to the k−ε model, it shows considerable difference according to how the redistributive pressure-strain term is modeled. Results of the RSM for countercurrent jets are improved with the modified coefficients for the dissipation rate, Cε1 and Cε2, suggested by Champion and Libby. Anisotropic states of the stress near the stagnation region are assessed in terms of an anisotropy invariant map (AIM).

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