scholarly journals LARGE EDDY SIMULATION OF AN ELLIPTIC JET INJECTED INTO A SUPERSONIC CROSSFLOW

2012 ◽  
Vol 19 ◽  
pp. 109-113
Author(s):  
GUO-LEI WANG ◽  
XI-YUN LU
Keyword(s):  
Large Eddy Simulation ◽  
Vortex Pair ◽  
Horseshoe Vortex ◽  
Mach Disk ◽  
Spanwise Direction ◽  
Complex Flow ◽  
Transverse Jet ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Features

A transverse jet issuing from an elliptic injector into a supersonic crossflow has been investigated using large eddy simulation. The complex flow structures and the relevant flow features are analyzed to exhibit the evolution of shock structures, vertical structures and jet shear layer. A horseshoe vortex is formed in the upstream of the jet and the shock structures exhibit small fluctuations due to the flow interaction. The kidney-shaped counter-rotating vortex pair dominates the flow field in the downstream of the jet. The elliptic jet spreads rapidly in the spanwise direction and then the axis-switching phenomenon occurs. Intense turbulent fluctuations are identified behind the Mach disk because of the large velocity gradients.

Large Eddy Simulation on the Interactions of Wake and Film-Cooling Near a Leading Edge

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
S. Sarkar ◽  
Harish Babu
Keyword(s):  
Large Eddy Simulation ◽  
Film Cooling ◽  
Vortex Pair ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Constant Thickness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Past A Cylinder ◽  
Downward Spiral

The unsteady flow physics due to interactions between a separated shear layer and film cooling jet apart from excitation of periodic passing wake are studied using large eddy simulation (LES). An aerofoil of constant thickness with rounded leading edge induced flow separation, while film cooling jets were injected normal to the crossflow a short distance downstream of the blend point. Wake data extracted from precursor LES of flow past a cylinder are used to replicate a moving bar that generates wakes in front of a cascade (in this case, an infinite row of the model aerofoils). This setup is a simplified representation of rotor-stator interaction in a film cooled gas turbine. The results of numerical simulation are presented to elucidate the formation, convection and breakdown of flow structures associated with the highly anisotropic flow involved in film cooling perturbed by convective wakes. The various vortical structures namely, horseshoe vortex, roller vortex, upright wake vortex, counter rotating vortex pair (CRVP), and downward spiral separation node (DSSN) vortex associated with film cooling are resolved. The effects of wake on the evolution of these structures are then discussed.

Large Eddy Simulation on the Interactions of Wake and Film-Cooling Near a Leading Edge

2014 ◽  
Author(s):  
Harish Babu ◽  
S. Sarkar
Keyword(s):  
Large Eddy Simulation ◽  
Film Cooling ◽  
Vortex Pair ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Constant Thickness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Past A Cylinder ◽  
Rotor Stator Interaction

The unsteady flow physics due to interactions between a separated shear layer and film cooling jet apart from excitation of periodic passing wake are studied using Large Eddy Simulation (LES). An aerofoil of constant thickness with rounded leading edge induced flow separation, while film cooling jets were injected normal to the crossflow a short distance downstream of the blend point. Wake data extracted from precursor LES of flow past a cylinder are used to replicate a moving bar that generates wakes in front of a cascade (in this case, an infinite row of the model aerofoils). This setup is a simplified representation of rotor-stator interaction in a film cooled gas turbine. The results of numerical simulation are presented to elucidate the formation, convection and breakdown of flow structures associated with the highly anisotropic flow involved in film cooling perturbed by convective wakes. The various vortical structures namely, horseshoe vortex, roller vortex, upright wake vortex, counter rotating vortex pair and DSSN vortex associated with film cooling are resolved. The effects of wake on the evolution of these structures are then discussed.

Large-Eddy Simulation of Turbulent Mixing of a Jet in Cross-Flow

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Mostafa Esmaeili ◽  
Asghar Afshari ◽  
Farhad A. Jaberi
Keyword(s):  
Large Eddy Simulation ◽  
Velocity Profile ◽  
Turbulent Mixing ◽  
Mass Density ◽  
Cross Flow ◽  
Vortex Pair ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Jet In Cross Flow ◽  
Large Eddy

An Eulerian–Lagrangian mathematical/computational methodology is employed for large-eddy simulation (LES) and detailed study of turbulent mixing in jet in cross-flow (JICF) configuration. Accurate prediction of mixing in JICF is crucially important to the development of advanced combustion systems. A high-order multiblock finite difference (FD) computational algorithm is used to solve the Eulerian velocity and pressure equations in a generalized coordinate system. The composition field, describing the mixing, is obtained from the filtered mass density function (FMDF) and its stochastic Lagrangian Monte-Carlo (MC) solver. Our simulations are shown to accurately predict the important flow features present in JICF such as the counter-rotating vortex pair (CVP), horseshoe, shear layer, and wake vortices. The consistency of the FD and MC parts of the hybrid LES/FMDF model is established for the simulated JICF in various conditions, indicating the numerical accuracy of the model. The effects of parameters influencing the jet penetration, entrainment, and turbulent mixing such as the jet velocity profile, and jet pulsation are investigated. The results show that the jet exit velocity profile significantly changes the trajectory and mixing of injected fluid. The jet pulsation is also shown to enhance the mixing depending on the flow Strouhal number. The LES/FMDF results are shown to be in good agreement with the available experimental data, confirming the reliability of LES/FMDF method for numerical simulation of turbulent mixing in complex flow configurations.

Numerical Study of Heat Transfer in a Row of Cylinders by 2D Large Eddy Simulation

2019 ◽  
Author(s):  
Andreas Stengaard Thorstensen ◽  
Andreas Krogh ◽  
Bjørn Christian Dueholm ◽  
Sebastian Bækkel Højte ◽  
Signe Birkebæk Thomasen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Large Eddy Simulation ◽  
Local Time ◽  
Numerical Study ◽  
Heat Transfer Analysis ◽  
Spanwise Direction ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Large Eddy

Abstract Complex flow structures arise as fluids are forced to flow across cylinder rows at moderate Reynolds numbers. In this study a numerical heat transfer analysis of 12 cylinders in an inline configuration is performed using Large Eddy Simulation (LES). The LES is conducted to get a better understanding of changes in the time averaged Nusselt number, 〈Nu〉, and local time averaged Nusselt number, 〈Nuθ〉, for each cylinder in the cylinder row. The simulations are performed at Re = UD/v = 10,000 and Pr = 0.71 with isothermal cylinders and a constant and uniform inflow temperature. The results show that the time averaged Nusselt number increases slightly between the first and second cylinder due to increased turbulent velocity fluctuations. Beyond the second cylinder, the time averaged Nusselt number decreases until it reaches a near constant value after the fifth cylinder. For all 12 cylinders the local time averaged Nusselt number around the surface is highest at the stagnation point. The first cylinder in the row has the same distribution as the reference simulation conducted for a single cylinder. From the second cylinder and onwards a larger part of the overall heat transfer is in the spanwise direction compared to the first- and reference cylinder.

scholarly journals Large-Eddy Simulation Study of Flow and Heat Transfer in Swirling and Non-Swirling Impinging Jets on a Semi-Cylinder Concave Target

2021 ◽  
Vol 11 (15) ◽  
pp. 7167
Author(s):  
Liang Xu ◽  
Xu Zhao ◽  
Lei Xi ◽  
Yonghao Ma ◽  
Jianmin Gao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Wall Temperature ◽  
Target Surface ◽  
Impinging Jets ◽  
Small Scale ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Large Eddy

Swirling impinging jet (SIJ) is considered as an effective means to achieve uniform cooling at high heat transfer rates, and the complex flow structure and its mechanism of enhancing heat transfer have attracted much attention in recent years. The large eddy simulation (LES) technique is employed to analyze the flow fields of swirling and non-swirling impinging jet emanating from a hole with four spiral and straight grooves, respectively, at a relatively high Reynolds number (Re) of 16,000 and a small jet spacing of H/D = 2 on a concave surface with uniform heat flux. Firstly, this work analyzes two different sub-grid stress models, and LES with the wall-adapting local eddy-viscosity model (WALEM) is established for accurately predicting flow and heat transfer performance of SIJ on a flat surface. The complex flow field structures, spectral characteristics, time-averaged flow characteristics and heat transfer on the target surface for the swirling and non-swirling impinging jets are compared in detail using the established method. The results show that small-scale recirculation vortices near the wall change the nearby flow into an unstable microwave state, resulting in small-scale fluctuation of the local Nusselt number (Nu) of the wall. There is a stable recirculation vortex at the stagnation point of the target surface, and the axial and radial fluctuating speeds are consistent with the fluctuating wall temperature. With the increase in the radial radius away from the stagnation point, the main frequency of the fluctuation of wall temperature coincides with the main frequency of the fluctuation of radial fluctuating velocity at x/D = 0.5. Compared with 0° straight hole, 45° spiral hole has a larger fluctuating speed because of speed deflection, resulting in a larger turbulence intensity and a stronger air transport capacity. The heat transfer intensity of the 45° spiral hole on the target surface is slightly improved within 5–10%.

Large eddy simulation study of turbulent flow around smooth and rough domes

2013 ◽  
Vol 227 (12) ◽  
pp. 2686-2700 ◽  
Author(s):  
N Kharoua ◽  
L Khezzar
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Flow Behavior ◽  
Pressure Coefficient ◽  
Horseshoe Vortex ◽  
Scale Model ◽  
Stream Velocity ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy

Large eddy simulation of turbulent flow around smooth and rough hemispherical domes was conducted. The roughness of the rough dome was generated by a special approach using quadrilateral solid blocks placed alternately on the dome surface. It was shown that this approach is capable of generating the roughness effect with a relative success. The subgrid-scale model based on the transport of the subgrid turbulent kinetic energy was used to account for the small scales effect not resolved by large eddy simulation. The turbulent flow was simulated at a subcritical Reynolds number based on the approach free stream velocity, air properties, and dome diameter of 1.4 × 105. Profiles of mean pressure coefficient, mean velocity, and its root mean square were predicted with good accuracy. The comparison between the two domes showed different flow behavior around them. A flattened horseshoe vortex was observed to develop around the rough dome at larger distance compared with the smooth dome. The separation phenomenon occurs before the apex of the rough dome while for the smooth dome it is shifted forward. The turbulence-affected region in the wake was larger for the rough dome.

Large Eddy Simulation of the Flow Around a Diffuser-Equipped Bluff Body in Ground Effect

2011 ◽  
Author(s):  
Lara Schembri Puglisevich ◽  
Gary Page
Keyword(s):  
Large Eddy Simulation ◽  
Bluff Body ◽  
Vortex Formation ◽  
Ground Effect ◽  
Vortical Flow ◽  
Navier Stokes ◽  
Flow Structures ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Features

Unsteady Large Eddy Simulation (LES) is carried out for the flow around a bluff body equipped with an underbody rear diffuser in close proximity to the ground, representing an automotive diffuser. The goal is to demonstrate the ability of LES to model underbody vortical flow features at experimental Reynolds numbers (1.01 × 106 based on model height and incoming velocity). The scope of the time-dependent simulations is not to improve on Reynolds-Averaged Navier Stokes (RANS), but to give further insight into vortex formation and progression, allowing better understanding of the flow, hence allowing more control. Vortical flow structures in the diffuser region, along the sides and top surface of the bluff body are successfully modelled. Differences between instantaneous and time-averaged flow structures are presented and explained. Comparisons to pressure measurements from wind tunnel experiments on an identical bluff body model shows a good level of agreement.

Very Large Eddy Simulation of Passive Drag Control for a D-Shaped Cylinder

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
Xingsi Han ◽  
Siniša Krajnović
Keyword(s):  
Large Eddy Simulation ◽  
Flow Control ◽  
Control Problem ◽  
Bluff Body ◽  
Numerical Study ◽  
Numerical Results ◽  
Complex Flow ◽  
Local Disturbance ◽  
Eddy Simulation ◽  
Large Eddy

The numerical study reported here deals with the passive flow control around a two-dimensional D-shaped bluff body at a Reynolds number of Re=3.6×104. A small circular control cylinder located in the near wake behind the main bluff body is employed as a local disturbance of the shear layer and the wake. 3D simulations are carried out using a newly developed very large eddy simulation (VLES) method, based on the standard k − ε turbulence model. The aim of this study is to validate the performance of this method for the complex flow control problem. Numerical results are compared with available experimental data, including global flow parameters and velocity profiles. Good agreements are observed. Numerical results suggest that the bubble recirculation length is increased by about 36% by the local disturbance of the small cylinder, which compares well to the experimental observations in which the length is increased by about 38%. A drag reduction of about 18% is observed in the VLES simulation, which is quite close to the experimental value of 17.5%. It is found that the VLES method is able to predict the flow control problem quite well.

A Dynamic Time Filtering Technique for Hybrid RANS-LES Simulation of Non-Stationary Turbulent Flow

2019 ◽  
Author(s):  
Tausif Jamal ◽  
D. Keith Walters
Keyword(s):  
Large Eddy Simulation ◽  
Comprehensive Evaluation ◽  
Model Performance ◽  
Turbulence Models ◽  
Mean Flow ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Filtering Technique ◽  
Dynamic Time

Abstract Unsteady turbulent wall bounded flows can produce complex flow physics including temporally varying mean pressure gradients, intermittent regions of high turbulence intensity, and interaction of different scales of motion. As a representative example, pulsating channel flow presents significant challenges for newly developed and existing turbulence models in computational fluid dynamics (CFD) simulations. The present study investigates the performance of the Dynamic Hybrid RANS-LES (DHRL) model with a newly proposed dynamic time filtering (DTF) technique, compared against an industry standard Reynolds-Averaged Navier-Stokes (RANS) model, Monotonically Integrated Large Eddy Simulation (MILES), and two conventional Hybrid RANS-LES (HRL) models. Model performance is evaluated based on comparison to previously documented Large Eddy Simulation (LES) results. Simulations are performed for a fully developed flow in a channel with time-periodic driving pressure gradient. Results highlight the relative merits of each model type and indicate that the use of a dynamic time filtering technique improves the accuracy of the DHRL model when compared to a static time filtering technique. A comprehensive evaluation of the results suggests that the DHRL-DTF method provides the most consistently accurate reproduction of the time-dependent mean flow characteristics for all models investigated.

Sign in / Sign up

Export Citation Format

Share Document