Numerical investigation of a confined jet flow in a rectangular cavity (original) (raw)
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Unsteady phenomena of an oscillating turbulent jet flow inside a cavity: Effect of aspect ratio
Journal of Fluids and Structures, 2009
Self-sustained oscillatory phenomena in confined flow may occur when a turbulent plane jet is discharging into a rectangular cavity. An experimental setup was developed and the flow analysis has been made using mainly hot-wire measurements, which were complemented by visualisation data. Previous studies confirmed that periodic oscillations may occur, depending on the location of the jet exit nozzle inside the cavity, and also the distance between the sidewalls. The present study deals with the symmetrical interaction between a turbulent plane jet and a rectangular cavity and the influence of the geometrical characteristics of the cavity on the oscillatory motion. The size and aspect ratio of the cavity were varied together with the jet width compared to that of the cavity. The study is carried out both numerically and experimentally. The numerical method solves the unsteady Reynolds averaged Navier-Stokes equations (URANS) together with the continuity equation for an incompressible fluid. The closure of the flow equations system is achieved using a two-scale energy-flux model at high Reynolds number in the core flow coupled with a wall function treatment in the vicinity of the wall boundaries. The fundamental frequency of the oscillatory flow was found to be practically independent of the cavity length. Moreover, the oscillations are attenuated as the cavity width increases, until they disappear for a critical value of the cavity width. Contour maps of the instantaneous flow field are drawn to show the flow pattern evolution at the main phases of oscillation. They are given for several aspect ratios of the cavity, keeping constant values for the cavity width and the jet thickness. The proposed approach may help to investigate further the oscillation mechanisms and the entrainment process occurring in pressure driven jet-cavity interactions.
Flow Turbulence and Combustion, 2001
The present work is devoted to the experimental and numerical study ofthe interaction of a turbulent plane jet with a rectangular cavity.Several flow regimes have been found to occur: the non-oscillationregime, the stable oscillation regime and an unstable oscillationregime. The first two regimes have been particularly considered. Theexperimental study has been carried out using hot wire anemometry andsome visualisations. The numerical predictions based on statisticalmodelling have been made using on the one hand the standard k–ε model and on the other hand a two-scales split spectrum model. The structuralproperties of the flow have been described for the different situations.For the oscillatory regime, a parametrical study allowed to determinethe influence of the jet exit location and the Reynolds number on thefrequency of the jet flapping. The one point closures have been able topredict the oscillatory regime, and in particular the two-scales modelled to improved results because better account is taken of lag effectsin unsteady non-equilibrium situations.
flowing inside a rectangular cavity Oscillatory phenomena of a turbulent plane jet
2002
and the Reynolds number. numerically in different situations : the location of the exit of the jet in the cavity of the stable-oscillation flow regime have been detailed experimentally and The structural properties of the flow and the frequency of the flapping of the jet oscillation regime, stable-oscillation regime and unstable-oscillation regime. have been observed for different positions of the jet inside the cavity : no(k - E) and the two-scales energy - flux-models. Three types of flow regimes on two statistical models of the turbulence : the mono-scale energy - dissipation anemometer and supplemented by visualizations. The numerical study is based in the cavity. The experimental study is made essentially by hot wire cavity is investigated under some conditions of the location of the exit of the jet In this study , the oscillation of a turbulent plane jet flowing inside a rectangular
Simulation of a Wall Jet Flow over a Rectangular Cavity
The simulation of a turbulent wall jet flow over a rectangular cavity is realised by the low Re stress-omega model. FLUENT 6.3 CFD code was used as the solver. The structured grid was built using Gambit 2.3. A preliminary study of a wall jet flow and a wall jet backward facing step interaction has been undertaken to validate the turbulence model. The numerical approach reproduces fairly the experimental results. A wall jet flow over rectangular cavities of different aspect ratios was investigated. The cavity aspect ratio effect on the flow structure evolution, particularly on the reattachment phenomenon, was examined in this paper. The results of this study show that the flow structure is very sensitive to the cavity aspect ratio. The reattachment length in the wall jet incoming flow case is very short compared to that of the boundary layer incoming flow case.
Study of the oscillatory regime of a turbulent plane jet impinging in a rectangular cavity
Applied Mathematical Modelling, 2003
The present work considers the general case of a turbulent plane jet flowing into a rectangular cavity. The study is relevant to a wide range of practical applications including forced convection, renewal of fluid inside a cavity and flowmeters. The experimental study considers the effect of the confinement on the jet characteristics. All the measurements are made using hot wire anemometry and complemented by visualisation of the various observed flow patterns. Numerical modelling has been carried out using two statistical models of the turbulence: the standard k-e model and a two-scale energy-flux model. The key feature of the multiple scale energy-flux model is the splitting of the turbulence spectrum devised for nonequilibrium turbulence modelling. Three flow regimes are observed depending on the location of the jet exit inside the cavity: oscillatory, transitional and steady. The oscillatory flow characteristics have been analysed from the structural and parametric points of view and the underlying mechanisms are discussed. The onepoint closure models proved to be able to reproduce the measured unsteady behaviour of the flow and some improvements are obtained using the multiple scale concept. (R. Schiestel). 0307-904X/02/$ -see front matter Ó 2002 Elsevier Science Inc. All rights reserved. PII: S 0 3 0 7 -9 0 4 X ( 0 2 ) 0 0 0 5 0 -1
Applied Mathematical Modelling, 2007
In this paper we present the results of numerical investigation of self-sustained oscillations of a jet confined in a symmetric cavity. This work represents an attempt to reproduce empirical observations of asymmetric flows in geometrically symmetric systems and to extend the jet flow investigations to more complex possible scenarios. A well-known example of such two-dimensional flow has been reported experimentally and reproduced numerically for simple flow [E. Schreck, M. Schaefer, Numerical study or bifurcation in three-dimensional sudden channel expansions, Comput. Fluids 29 (2000) 583-593]. It has been found that for some particular control parameter, above its critical value (bifurcation point), the jet can be deflected to either of the two sides of the cavity. In this paper we report a similar behaviour which is, however, characterized by a more complicated flow pattern. While simple flow appears only within small cavity lengths the complex flows develops with increased cavity lengths. Unlike stationary asymmetric solutions accompanied by cavity jet oscillations, as experimentally reported in e.g., [A. Maurel, P. Ern, B.J.A. Zielinska, J.E. Wesfreid, Experimental study of self-sustained oscillations in a confined jet, Phys Rev. E 54 (1996) 3643-3651], in our investigations of both simple and complex asymmetric flow we observed the slow periodical drift of the jet from one to another side of the cavity. The essential control parameters were Reynolds number Re and the ratio length to inlet width L/d. According to experiments of , the jet is stable and symmetric, when both L/d and Re are below certain critical values, otherwise jet oscillations appear in both experiment and our simulation (cavity oscillations regime). However, further increase of either (or both) L/d and Re leads of so called free jet type oscillations regime. This paper describes complex jet behaviour within the later oscillations regime. We believe that both simple ''classical'' and ''our'' complex stationary asymmetric solutions (as well as superimposed cavity-type and free-jet oscillations) can be explained based on physical arguments as already done in previous works. However, the origin of slow drift motion remains still to be resolved. This might be of high importance for clear distinguishing between relevant physical and numerical features in future codes developments.
Steady interaction of a turbulent plane jet with a rectangular heated cavity
Thermal Science, 2014
Turbulent heat transfer between a confined jet flowing in a hot rectangular cavity is studied numerically by finite volume method using the k-w SST one point closure turbulence model. The location of the jet inside the cavity is chosen so that the flow is in the non-oscillation regime. The flow structure is described for different jet-to-bottom-wall distances. A parametrical study was conducted to identify the influence of the jet exit location and the Reynolds number on the heat transfer coefficient. The parameters of this study are: the jet exit Reynolds number (Re, 1560< Re <33333), the temperature difference between the cavity heated wall and the jet exit (DT=60?C) and the jet location inside the cavity (Lf, 2? Lf? 10 and Lh 2.5
Jet-cavity interaction: effect of the cavity depth
Progress in Computational Fluid Dynamics, An International Journal, 2012
ABSTRACT A two-dimensional turbulent wall jet over a shallow cavity is studied numerically. The present paper investigates the wall jet outer layer effect on a shallow cavity flow structure. This layer is an important turbulence source which is added to that of the inner shear layer. It was found that the reattachment process seems to be accelerated in the turbulent wall jet incoming flow compared to that of the cavity in duct flow. The present study shows that the flow structure is very sensitive to the cavity depth to nozzle height ratio; the increasing of this ratio induces a reattachment length decrease.
Control of self-sustained jet oscillations in 3D thin rectangular cavity
Chemical Engineering Research and Design, 2017
The aim of this work is the control of an oscillatory jet submerged in a 3D thin rectangular cavity, with two opposite injections added on its thinnest sidewalls at the same height, perpendicular and above the jet exit. This type of control is required when the characteristics of the main jet (Reynolds number, nozzle size) are not modifiable. Due to Coanda effect, the oscillations of the main jet occur in the widest plane of the cavity, and depend on the mass flow of two injections. Unsteady, 3D problem is solved by finite volume method using URANS modeling. The validation confirms that second order models predict more accurately this flow configuration than first order models. Two behaviors of time average of flow fields corresponding for two ranges of ˇ are detected. When 0 ≤ ˇ <25.51%, the main jet effect decreases to reach the case without lateral injections (ˇ = 0). Similarly for 25.51 ≤ ˇ≤ 50.67%, the main jet effect diminishes for higher value of ˇ. Thus, ˇ = 25.51% is a threshold value for this type of flow configuration. Moreover, for ˇ = 25.51% the minimum values for the kinetic energy, main jet deflection angle and oscillations frequency are reached. Furthermore, the deflection angle reaches its maximum value for ˇ = 12.90% and the best deflections are recommended for ˇ < 25.51%.
Numerical Validation of a Coaxial and Confined Jet Flow
Icheap-10: 10th International Conference on Chemical and Process Engineering, Pts 1-3, 2011
The purpose of this study is to investigate experimentally and numerically the flow behavior of a confined coaxial jet flow for two different velocity ratios Ru=0.04 and Ru=0.08. For the experimental analysis a two dimension particle image velocimetry system (2D-PIV) is used to measure the gas behavior in the measurement section. The numerical analysis is developed for four different Reynolds Average Navier-Stokes models: standard k-, k-ω, SST and RSM. The experimental and numerical results are presented in radial profiles in two different axial positions (L/D=3 and L/D=6) in terms of axial mean velocity and turbulence kinetic energy. All turbulence models showed a good qualitatively agreement in relation to the axial mean velocity analysis. However, the turbulence kinetic energy analysis showed that the Reynolds Stress model can better describe the flow behavior in the confined coaxial jet.