Three-dimensional study of turbulent flow characteristics of an offset plane jet with variable density (original) (raw)
Related papers
Axisymmetric wall jet development in confined jet impingement
Physics of Fluids
The flow field surrounding an axisymmetric, confined, impinging jet was investigated with a focus on the early development of the triple-layered wall jet structure. Experiments were conducted using stereo particle image velocimetry at three different confinement gap heights (2, 4, and 8 jet diameters) across Reynolds numbers ranging from 1000 to 9000. The rotating flow structures within the confinement region and their interaction with the surrounding flow were dependent on the confinement gap height and Reynolds number. The recirculation core shifted downstream as the Reynolds number increased. For the smallest confinement gap height investigated, the strong recirculation caused a disruption of the wall jet development. The radial position of the recirculation core observed at this small gap height was found to coincide with the location where the maximum wall jet velocity had decayed to 15% of the impinging jet exit velocity. After this point, the self-similarity hypothesis failed to predict the evolution of the wall jet further downstream. A reduction in confinement gap height increased the growth rates of the wall jet thickness but did not affect the decay rate of the wall jet maximum velocity. For jet Reynolds numbers above 2500, the decay rate of the maximum velocity in the developing region of the wall jet was approximately 1.1, which is close to previous results reported for the fully developed region of radial wall jets. A much higher decay rate of 1.5 was found for the wall jet formed by a laminar impinging jet at Re = 1000.
Comparative study of flow characteristics of a single offset jet and a turbulent dual jet
Heat and Mass Transfer, 2018
The present paper consists of a numerical investigation of dynamic and thermal characteristics of the flow field resulting from the interaction of dual-jet consisting of a wall jet and an offset jet and comparison with a single turbulent offset jet. The effects of velocity and offset ratios between two jets in the near field region have been simulated numerically using two-dimensional steady RANS equations. The simulation is carried out through the resolution of the different governing Navier-Stokes' equations by means of the finite volume method. Two different closure models were tested: the standard k-e model and the Reynolds stress model (RSM) second order model. A non-uniform mesh system tightened close to the emitting nozzle and both the vertical and horizontal walls is also adopted. The confrontation of the numerical results with experimental data from literature shows satisfying agreement with the RSM model in the description of the handled flow; that's why we adopted it for the rest of the paper. Once the model validated, a detailed discussion has been provided on the mean velocities, pressure field, Reynolds stress, and kinetic energy. The merge point, the combined point and the impact point have also been obtained and compared with other results. A similarity profile has been obtained in the downstream direction for different offset and velocity ratios.
Experimental Analysis of Axisymmetric Impinging Jet Flow
Journal of Engineering and Applied Science
An experimental study of fully developed confined impinging axisymmetric water vapor jet is completed with turbulent characteristics measured when this jet impinges normal to a flat plate. The velocity measurements are made using laser Doppler anemometer (LDA). The flow is illuminated by a sheet of light obtained by spreading a laser beam and the flow patterns are recorded using a digital camera to observe different flow regions and the impact of presence of upper surface on flow pattern. Flow field and velocities are investigated for both straight and contoured jet tube exits.
Investigation of a Compound Wall Jet in the Vicinity of Jet Exit
International Conference on Aerospace Sciences and Aviation Technology, 1993
Wind tunnel tests are conducted to study the effect of upper surface blowing on aerodynamic characteristics. A wall jet is issued tangent to a flat plate that forms the upper surface of an airfoil at zero angle of attack. The leading edge of the airfoil is NACA 0015. The effect of chordwise blowing on the aerodynamic load is studied through investigation of the pressure distribution on the flat surface. The pressure coefficient shows two consecutive sharp peaks resulting in two adverse pressure gradients. Higher peaks are obtained for the higher jet/free stream velocity ratios. This feature indicates the complicated structure of the vortex flow in the transition region along the flat plate surface. In addition to the investigation of the aerodynamic load, the effect of upper surface blowing on the mean velocity, turbulence and Reynolds shear stress of the flow field is illustrated. It is found that the chordwise mean velocity profiles are similar in the free mixing region. As the jet/free stream velocity ratio becomes more than unity, jet blowing activates the mean upward lateral velocity which increases with increasing jet velocity. The inflection points of mean velocity profiles are accompanied by peaks of turbulence and Reynolds shear stress. Likewise, both normal and turbulent shear stress profiles exhibit the similarity episode.
Characterisation of confinement and impingement effects on the near field of axisymmetric jets
Laser Techniques for Fluid Mechanics, 2002
Laser Doppler Anemometry and Particle Image Velocimetry are applied to a domestic burner configuration to determine the effect of geometrical parameters and gas density on the flow field and on the entrainment process. The flow field is that of a confined jet impinging onto a plate. The main design parameters of the experimental devices may be adjusted to modify the confinement ratio and the distance from the outer section of the injector to the stagnation plate. The impinging distance is known to influence the structure of the flow field, mostly when the stagnation plate is in the near field region of the jet. Two density ratios were studied: an isodensity (R ρ = 1) and a light jet (R ρ = 0.55). The two nominal flow rates were investigated, associated with low Reynolds turbulent jets and laminar jets. A totally transparent new device was manufactured in quartz. This new device presents greater optical accesses for PIV measurements inside the burner. Several configurations were investigated for the different gases and impinging distances: free jets, confined jets, impinging jets, and confined impinging jets (whole burner configurations). The results concentrate on the jet development and the dynamic field in the vicinity of the stagnation point. The structure of the flow field was investigated in terms of 2D dynamic fields, axial and radial profiles of velocity. A new derivation method for intercorrelation (Hart) is compared with classic FFT intercorrelation, bringing better resolution in the zones of highest velocity gradients. To guarantee high accuracy of the measurements for the whole flow field, two sets of experiments had to be conducted, with two different PIV pulse delay values: one to match the higher velocities encountered in the jet part and the other the lower velocities encountered in the entrainment part. The flow field consists in a combination of these two sets of experiments. The radial jets profiles allow to deduce the entrained air flow rate, against the distance of the stagnation plate as a function of the density ratio. The amount of air entrained by the jet is linked to the density ratio, the length of jet development and also to the pressure gradient due to the impact on the plate. An analysis of the mixture fraction distribution using planar LIF images is in progress.
T he flow field characteristics of multiple wall jets issuing from cylindrical surfaces in still air, their mutual interaction, separation and reattachment to the wall are experimentally investigated. The effects of cylinder curvature and pitch between jets are studied. Mean velocity distribution in both spanwise and normal planes was measured using both pressure probes and a hot wire anemometer. Good agreement for the results of the two techniques has been obtained. Surface curvature seldom has an effect on merging between in-line jets, but it affects the reat-tachment length on the wall. In the spanwise direction, the jet growth rate increases as the pitch decreases. There is good agreement between the reattachment lengths determined by the hot wire anemometer and those obtained by flow vi-sualization using the oil film technique. The effect of the wall offset from jets on the flow field was also investigated. The results indicate that as the distance between the wall and jets increases, the growth rate of the jet decreases and causes maximum velocity deviation towards the wall. Increasing the offset of the wall also delays both the merging between jets and reattachment to the wall. Local turbulence intensity and root mean square value in normal direction are measured downstream the jets.
Bench-Scale Investigation of Inclined Dense Jets
Journal of Hydraulic Engineering, 2005
ABSTRACT In this work experimental data on the geometry of dense inclined jets issuing in a lab-scale glass rectangular tank are presented. The surrounding fluid was always tap water at room temperature while the dense jets were water solutions of NaCl. Four parameters were changed in the experiments, namely nozzle diameter and inclination, and jet density and flow rate. Jet trajectories were revealed by a colored tracer. Images of the jet were recorded by a digital camera and then further digitally processed, eventually resulting in a time-averaged tracer intensity field. All the jet geometrical parameters, once normalized, were found to be very well correlated to the densimetric Froude number. Moderate jet viscosity variations were found to not significantly affect jet behavior. The reported data allow a quick and easy estimation of maximum rise level, position of the trajectory maximum, and impact point distance of dense jets issued at different angles above the horizontal. Journal of Hydraulic Engineering
Hydrodynamics of submerged turbulent plane offset jets
Physics of Fluids, 2017
The results of an experimental study on the turbulent flow characteristics in submerged plane offset jets are presented. The vertical profiles of time-averaged velocity components and Reynolds stresses at different horizontal locations are depicted to illustrate their variations across the pre-attachment, impingement, and wall jet regions. The characteristic lengths and the jet profile of submerged offset jets in the pre-attachment region are determined from the velocity profiles. The regional profiles of velocity and Reynolds stresses are analyzed in the context of the self-similarity, the decay of their representative scales, and the development of the length scales. The self-similarity characteristics in the pre-attachment and wall jet regions are preserved better than those in the impingement region. The turbulent kinetic energy (TKE) fluxes suggest that within the jet layer in the pre-attachment region, an upward advection of low-speed fluid streaks induces a strong retardation to the jet; while in the wall jet region, an inrush of low-speed fluid streaks induces a weak retardation. Analysis of the TKE budget reveals that within the jet layer, the TKE diffusion rate and the pressure energy diffusion rate oppose each other, and the peaks of the dissipation rate lag from those of the corresponding production rate.