Direct numerical simulation of a wall jet: flow physics

A direct numerical simulation (DNS) of a plane wall jet is performed at a Reynolds number of $Re_{j}=7500$. The streamwise length of the domain is long enough to achieve self-similarity for the mean flow and the Reynolds shear stress. This is the highest Reynolds number wall jet DNS for a large domain achieved to date. The high resolution simulation reveals the unsteady flow field in great detail and shows the transition process in the outer shear layer and inner boundary layer. Mean flow parameters of maximum velocity decay, wall shear stress, friction coefficient and jet spreading rate are consistent with several other studies reported in the literature. Mean flow, Reynolds normal and shear stress profiles are presented with various scalings, revealing the self-similar behaviour of the wall jet. The Reynolds normal stresses do not show complete similarity for the given Reynolds number and domain length. Previously published inner layer budgets based on LES are inaccurate and those that have been measured are only available in the outer layer. The current DNS provides fully balanced, explicitly calculated budgets for the turbulence kinetic energy, Reynolds normal stresses and Reynolds shear stress in both the inner and outer layers. The budgets are scaled with inner and outer variables. The inner-scaled budgets in the near wall region show great similarity with turbulent boundary layers. The only remarkable difference is for the turbulent diffusion in the wall-normal Reynolds stress and Reynolds shear stress budgets. The outer layer interacts with the inner layer through turbulent diffusion and the excess energy from the wall-normal direction is transferred to the spanwise direction.</jats:p

Direct numerical simulation of a wall jet: flow physics

The authors greatly acknowledge the United Kingdom Turbulence Consortium (UKTC), under EPSRC grant EP/L000261/1, for providing compute time on ARCHER, the UK National Supercomputing Service (http://www.archer.ac.uk) for these simulations

Analysis of second moment closure modeling for a rectangular surface jet using dns data

Results for a DNS of a horizontal, rectangular turbulent surface jet of aspect ratio 2:1 at a Reynolds number of 4,420 issuing into a quiescent medium are presented. The simulation is validated against experimental data. The DNS results are used to investigate sub-models used in the RANS “Basic Model” and TCL model. It is shown that the pressure-strain correlation and dissipation anisotropy models incompletely describe the near surface behaviour. These deficiencies negatively impact the prediction of the jet spreading rate and the existence of the surface layer associated with fast variations of the horizontal vorticity component

Body force modelling of internal geometry for jet noise prediction

The noise produced by aeroengines is a critical topic in engine design. Large-Eddy Simulation (LES) and hybrid Reynolds-Averaged Navier-Stokes (RANS)-LES provides amethod to increase understanding of influences on the noise produced and could lead to improved models for use in design. Use of Immersed Boundary (IB) and Body Force Methods (BFM) allows arbitrary geometry to be added rapidly and so this is explored to model internal geometry effects on jet noise. This reduces grid complexity and broadens the accessible design space by reducing setup time and computational cost. Using LES and BFM/IB, many effects that are difficult to test experimentally can be assessed numerically within useful timeframes. To enable challenging targets for jet noise to be met, the importance of the many influences on jet noise must be understood. These include the use of, single or dual stream jet nozzles, the presence (or lack of) of a pylon, wing, flap and deflection angles, nozzle serrations, eccentricity, temperature and velocity ratio, flight stream and upstream/internal geometry effects. The latter effects are the main focus of this study

Cost-effective hybrid RANS-LES type method for jet turbulence and noise prediction

Jets at higher Reynolds numbers have a high concentration of energy in small scales in the nozzle vicinity. This is challenging for large-eddy simulation, potentially placing severe demands on grid density. To circumvent this, we propose a novel procedure based on well-known Reynolds number (Re) independent of jets. We reduce the jet Re while rescaling the boundary layer properties to maintain incoming boundary layer thickness consistent with high Re jet. The simulations are carried out using hybrid large-eddy simulation type of approach which is incorporated by using near-wall turbulence model with modified properties. No subgrid scale model is used in these simulations. Hence, they effectively become numerical large-eddy simulation with Reynolds-averaged Navier–Stokes covering the full boundary layer region. The noise post-processing is carried out using the Ffowcs-Williams-Hawking approach. The simulations are made for Mach numbers (M) of 0.75 and 0.875 (cold and hot). The results for the overall sound pressure level are observed to be within 2–3% of the measurements, and directivity of sound is also captured accurately for both the cases. Hence, the low Re simulations can be more beneficial in saving time and cost while providing reasonably accurate results