Direct Numerical Simulation of the Transition to Turbulence in a Supersonic Boundary Layer on Smooth and Rough Surfaces

2017 ◽  
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Direct Numerical Simulation ◽  
Rough Surfaces ◽  
Supersonic Boundary Layer ◽  
Transition To Turbulence

Direct Numerical Simulation and Large Eddy Simulation of Laminar Separation Bubbles at Moderate Reynolds Numbers

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Francois Cadieux ◽  
Julian A. Domaradzki ◽  
Taraneh Sayadi ◽  
Sanjeeb Bose
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Boundary Layer ◽  
Direct Numerical Simulation ◽  
Separation Bubble ◽  
Leading Edge ◽  
Transition To Turbulence ◽  
Laminar Separation Bubble ◽  
Laminar Separation ◽  
Large Eddy

Flows over airfoils and blades in rotating machinery for unmanned and microaerial vehicles, wind turbines, and propellers consist of different flow regimes. A laminar boundary layer near the leading edge is often followed by a laminar separation bubble with a shear layer on top of it that experiences transition to turbulence. The separated turbulent flow then reattaches and evolves downstream from a nonequilibrium turbulent boundary layer to an equilibrium one. Typical Reynolds-averaged Navier–Stokes (RANS) turbulence modeling methods were shown to be inadequate for such laminar separation bubble flows (Spalart and Strelets, 2000, “Mechanisms of Transition and Heat Transfer in a Separation Bubble,” J. Fluid Mech., 403, pp. 329–349). Direct numerical simulation (DNS) is the most reliable but is also the most computationally expensive alternative. This work assesses the capability of large eddy simulations (LES) to reduce the resolution requirements for such flows. Flow over a flat plate with suitable velocity boundary conditions away from the plate to produce a separation bubble is considered. Benchmark DNS data for this configuration are generated with the resolution of 59 × 106 mesh points; also used is a different DNS database with 15 × 106 points (Spalart and Strelets, 2000, “Mechanisms of Transition and Heat Transfer in a Separation Bubble,” J. Fluid Mech., 403, pp. 329–349). Results confirm that accurate LES are possible using O(1%) of the DNS resolution.

Direct numerical simulation of transition to turbulence in Görtler flow

1993 ◽  
Vol 246 ◽  
pp. 267-299 ◽  
Author(s):  
Wei Liu ◽  
J. Andrzej Domaradzki
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Direct Numerical Simulation ◽  
Linear Stability ◽  
Stokes Equations ◽  
Vertical Direction ◽  
Velocity Profiles ◽  
Vertical Shear ◽  
Transition To Turbulence ◽  
Concave Wall

Using direct numerical simulation techniques we investigate transition to turbulence in a boundary-layer flow containing two large-scale counter-rotating vortices with axes aligned in the streamwise direction. The vortices are assumed to have been generated by the Görtler instability mechanism operating in boundary-layer flows over concave walls. Full, three-dimensional Navier–Stokes equations in a natural curvilinear coordinate system for a flow over concave wall are solved by a pseudospectral numerical method. The simulations are initialized with the most unstable mode of the linear stability theory for this flow with its amplitude taken from the experimental measurements of Swearingen & Blackwelder (1987). The evolution of the Görtler vortices for two different spanwise wavenumbers has been investigated. In all cases the development of strong inflexional velocity profiles is observed in both spanwise and vertical directions. The instabilities of these velocity profiles are identified as a primary mechanism of the transition process. The results indicate that the spanwise shear plays a more prominent role in the transition to turbulence than the vertical shear, in agreement with the hypothesis originally proposed by Swearingen & Blackwelder (1987). The following features of the transition, consistent with this hypothesis, were observed. Instability oscillations start in the spanwise direction and are followed later by oscillations in the vertical direction. A two-dimensional linear stability analysis predicts that the maximum growth rates of perturbations associated with the spanwise profiles are greater than those associated with the vertical profiles. Regions of high perturbation velocity correlate well with the regions of high spanwise shear and no obvious correlation with the vertical shear regions is observed. Finally, the analysis of the kinetic energy balance equation reveals that most of the perturbation energy production in the initial stages of transition occurs in the region characterized by large spanwise shear created by the action of the vortices moving low-speed fluid away from the wall. Our results are consistent qualitatively and quantitatively with other experimental, theoretical, and numerical investigations of this flow.

scholarly journals Experimental and numerical investigation of excitation of artificial disturbances in the supersonic boundary layer

2019 ◽  
Vol 196 ◽  
pp. 00017
Author(s):  
Aleksey Yatskikh ◽  
Aleksander Semenov ◽  
Gleb Kolosov ◽  
Aleksander Kosinov ◽  
Yury Yermolaev
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Direct Numerical Simulation ◽  
Flat Plate ◽  
Numerical Investigation ◽  
Plate Boundary ◽  
Supersonic Boundary Layer ◽  
Pulsed Discharge ◽  
Pulse Injection ◽  
Flat Plate Boundary Layer

The influence of the parameters of the impulse action on the laminar supersonic flat-plate boundary layer on the excited localized perturbations is investigated at Mach 2. The influence of the duration of a pulsed discharge on the generated disturbances is studied experimentally. Also, a direct numerical simulation of the influence of the parameters of pulse injection on generated perturbations is carried out. It is obtained that as the duration of the action on the supersonic boundary layer increases, the amplitude of the generated disturbance increases. The velocity of the propagation downstream of localized disturbances in Mach 2 supersonic flat-plate boundary layer is estimated.

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