Evaluation of Reattaching Shear-Layer in Compressible Turbulent Flows: A Large Eddy Simulation Approach

2020 ◽  
Author(s):  
Rozie Zangeneh
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Shear Layer ◽  
Turbulent Flows ◽  
High Speed ◽  
High Fidelity ◽  
Free Shear Layer ◽  
Eddy Simulation ◽  
Shock Unsteadiness ◽  
Large Eddy

Abstract The boundary-layer separation and subsequent reattachment due to the free shear-layer and Shockwave interaction have a significant impact on the aerothermal design of supersonic aerospace systems. This problem is prevalent in high-speed flights and can significantly affect the skin friction, aerodynamic loads, and heat transfer. In recent years, considerable progress has been achieved in the prediction of turbulent compressible flows using high-fidelity models. However, the prediction of reattaching free shear-layer and shockwave interactions still needs to be modified for accurate predictivity. The objective of this study is to investigate the ability of a new computational fluid dynamics model to predict these critical flow phenomena accurately. The new high-fidelity model is based on a collocated central scheme, which has the advantage of being a Riemann free solver, and therefore easy to implement on unstructured grids. It is developed to capture any discontinuities at shocks while it is able to capture broadband spatial and temporal variations in turbulent flows with minimal dissipation and dispersion. Large Eddy Simulation is performed on a compression corner at a Mach number of 2.92 and a high Reynolds number. The geometry of the model is specifically designed to isolate the reattachment process of a high-speed separated flow. To examine the accuracy of the predicted results, results of velocity profiles in the free shear-layer, boundary layer development, turbulent fluctuations, and pressure are compared to an experimental effort by Princeton. Excellent agreement is observed, and it is recommended that the model can be used to investigate the physics of the shock unsteadiness due to interaction with a free shear-layer.

scholarly journals Large Eddy Simulation of Microbubble Drag Reduction in Fully Developed Turbulent Boundary Layers

2020 ◽  
Vol 8 (7) ◽  
pp. 524
Author(s):  
Tongsheng Wang ◽  
Tiezhi Sun ◽  
Cong Wang ◽  
Chang Xu ◽  
Yingjie Wei
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Eddy Simulation ◽  
Drag Reduction ◽  
High Speed ◽  
Streamwise Velocity ◽  
Burst Frequency ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Good Agreement

Microbubble drag reduction has good application prospects. It operates by injecting a large number of bubbles with tiny diameters into a turbulent boundary layer. However, its mechanism is not yet fully understood. In this paper, the mechanisms of microbubble drag reduction in a fully developed turbulent boundary layer over a flat-plate is investigated using a two-way coupled Euler-Lagrange approach based on large eddy simulation. The results show good agreement with theoretical values in the velocity distribution and the distribution of fluctuation intensities. As the results show, the presence of bubbles reduces the frequency of bursts associated with the sweep events from 637.8 Hz to 611.2 Hz, indicating that the sweep events, namely the impacting of high-speed fluids on the wall surface, are suppressed and the streamwise velocity near the wall is decreased, hence reducing the velocity gradient at the wall and consequently lessening the skin friction. The suppression on burst frequency also, with the fluid fluctuation reduced in degree, decreases the intensity of vortices near the wall, leading to reduced production of turbulent kinetic energy.

scholarly journals Unsteady Adjoint of Pressure Loss for a Fundamental Transonic Turbine Vane

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Chaitanya Talnikar ◽  
Qiqi Wang ◽  
Gregory M. Laskowski
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Adjoint Equations ◽  
High Fidelity ◽  
Trailing Edge ◽  
Eddy Simulation ◽  
Large Eddy ◽  
High Fidelity Simulations ◽  
Unsteady Adjoint ◽  
Adjoint Solutions

High-fidelity simulations, e.g., large eddy simulation (LES), are often needed for accurately predicting pressure losses due to wake mixing and boundary layer development in turbomachinery applications. An unsteady adjoint of high-fidelity simulations is useful for design optimization in such aerodynamic applications. In this paper, we present unsteady adjoint solutions using a large eddy simulation model for an inlet guide vane from von Karman Institute (VKI) using aerothermal objectives. The unsteady adjoint method is effective in capturing the gradient for a short time interval aerothermal objective, whereas the method provides diverging gradients for long time-averaged thermal objectives. As the boundary layer on the suction side near the trailing edge of the vane is turbulent, it poses a challenge for the adjoint solver. The chaotic dynamics cause the adjoint solution to diverge exponentially from the trailing edge region when solved backward in time. This results in the corruption of the sensitivities obtained from the adjoint solutions. An energy analysis of the unsteady compressible Navier–Stokes adjoint equations indicates that adding artificial viscosity to the adjoint equations can dissipate the adjoint energy while potentially maintaining the accuracy of the adjoint sensitivities. Analyzing the growth term of the adjoint energy provides a metric for identifying the regions in the flow where the adjoint term is diverging. Results for the vane obtained from simulations performed on the Titan supercomputer are demonstrated.

A modified blending function for zonal hybrid Reynolds-averaged Navier—Stokes/large-eddy simulation methodology

2009 ◽  
Vol 223 (8) ◽  
pp. 1067-1081 ◽  
Author(s):  
M B Sun ◽  
J H Liang ◽  
Z G Wang
Keyword(s):  
Boundary Layer ◽  
Supersonic Flow ◽  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Navier Stokes ◽  
Empirical Constant ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes ◽  
Blending Function

A modified blending function for zonal hybrid Reynolds averaged Navier—Stokes/large eddy simulation (RANS/LES) methodology was developed using an empirical analogy from Menter k—ω shear stress transport (SST) turbulent model (Menter, 1994) to predict complex turbulent flows. Tests of slot jet in supersonic flow and supersonic flow over compression—expansion ramp was conducted and prediction of separations was well improved when certain model constant was forced on the traditional blending function (Baurle et al., 2003). Analysis based on calculations of flat plate boundary layer demonstrated that an efficient empirical constant could be used in blending function and boundary layer could be well calculated without heavy contamination of RANS on wake region. Validation of the modified zonal hybrid RANS/LES approach for slot jet in supersonic flow, supersonic flow over compression—expansion ramp, supersonic flow over backward facing step, and supersonic cavity flow was conducted. The simulated results showed that the modified blending function performs well on complex turbulent flows. Deficiencies of traditional hybrid zonal RANS/LES method in over-prediction of separations associated with adverse pressure gradient flows were favourably improved.

scholarly journals Unsteady Adjoint of Pressure Loss for a Fundamental Transonic Turbine Vane

2016 ◽  
Author(s):  
Chaitanya Talnikar ◽  
Qiqi Wang ◽  
Gregory M. Laskowski
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Adjoint Equations ◽  
High Fidelity ◽  
Trailing Edge ◽  
Eddy Simulation ◽  
Large Eddy ◽  
High Fidelity Simulations ◽  
Unsteady Adjoint ◽  
Adjoint Solutions

High fidelity simulations, e.g., large eddy simulation are often needed for accurately predicting pressure losses due to wake mixing and boundary layer development in turbomachinery applications. An unsteady adjoint of high fidelity simulations is useful for design optimization in such aerodynamic applications. In this paper we present unsteady adjoint solutions using a large eddy simulation model for a vane from VKI using aerothermal objectives. The unsteady adjoint method is effective in capturing the gradient for a short time interval aerothermal objective, whereas the method provides diverging gradients for long time-averaged thermal objectives. As the boundary layer on the suction side near the trailing edge of the vane is turbulent, it poses a challenge for the adjoint solver. The chaotic dynamics cause the adjoint solution to diverge exponentially from the trailing edge region when solved backwards in time. This results in the corruption of the sensitivities obtained from the adjoint solutions. An energy analysis of the unsteady compressible Navier-Stokes adjoint equations indicates that adding artificial viscosity to the adjoint equations can dissipate the adjoint energy while potentially maintain the accuracy of the adjoint sensitivities. Analyzing the growth term of the adjoint energy provides a metric for identifying the regions in the flow where the adjoint term is diverging. Results for the vane from simulations performed on the Titan supercomputer are demonstrated.

Large eddy simulation of shock/boundary-layer interaction

AIAA Journal ◽  
2002 ◽  
Vol 40 ◽  
pp. 1935-1944 ◽  
Author(s):  
E. Garnier ◽  
P. Sagaut ◽  
M. Deville
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Layer Interaction ◽  
Eddy Simulation ◽  
Shock Boundary Layer Interaction ◽  
Large Eddy ◽  
Boundary Layer Interaction
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