Investigation of Transition and Separation in the Presence of Free Stream Turbulence Using Direct Numerical Simulation

2012 ◽  
Author(s):  
Shirzad Hosseinverdi ◽  
Hermann Fasel
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Free Stream ◽  
Free Stream Turbulence

Direct numerical simulation of flow past a transversely rotating sphere up to a Reynolds number of 300 in compressible flow

2018 ◽  
Vol 857 ◽  
pp. 878-906 ◽  
Author(s):  
T. Nagata ◽  
T. Nonomura ◽  
S. Takahashi ◽  
Y. Mizuno ◽  
K. Fukuda
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Mach Number ◽  
Direct Numerical Simulation ◽  
Drag Coefficient ◽  
Rotation Rate ◽  
Free Stream ◽  
Rotating Sphere ◽  
Free Stream Mach Number ◽  
Low Reynolds

In this study, direct numerical simulation of the flow around a rotating sphere at high Mach and low Reynolds numbers is conducted to investigate the effects of rotation rate and Mach number upon aerodynamic force coefficients and wake structures. The simulation is carried out by solving the three-dimensional compressible Navier–Stokes equations. A free-stream Reynolds number (based on the free-stream velocity, density and viscosity coefficient and the diameter of the sphere) is set to be between 100 and 300, the free-stream Mach number is set to be between 0.2 and 2.0, and the dimensionless rotation rate defined by the ratio of the free-stream and surface velocities above the equator is set between 0.0 and 1.0. Thus, we have clarified the following points: (1) as free-stream Mach number increased, the increment of the lift coefficient due to rotation was reduced; (2) under subsonic conditions, the drag coefficient increased with increase of the rotation rate, whereas under supersonic conditions, the increment of the drag coefficient was reduced with increasing Mach number; and (3) the mode of the wake structure becomes low-Reynolds-number-like as the Mach number is increased.

Direct Numerical Simulation of Turbulent Boundary Layer Downstream of Turbulence-Generating Grid

2007 ◽  
Author(s):  
H. Suzuki ◽  
K. Nagata ◽  
Y. Sakai ◽  
T. Hayase ◽  
T. Kubo
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Direct Numerical Simulation ◽  
Free Stream ◽  
Grid Turbulence ◽  
Governing Equations ◽  
Step Method ◽  
Fractional Step Method ◽  
Log Law

The effects of external grid turbulence in a free stream on the turbulent boundary layer are investigated by means of the direct numerical simulation (DNS). A square turbulence-generating grid, on which the velocity components are set to zero, is located upstream of the flat boundary with a nonslip condition. The fractional step method is used to solve the governing equations. The results show that turbulence intensities and Reynolds stress normalized by the inner parameters are significantly suppressed in the log-law region by the external grid turbulence.

Direct Numerical Simulation of By-Pass and Separation-Induced Transition in a Linear Compressor Cascade

2006 ◽  
Author(s):  
Tamer Zaki ◽  
Paul Durbin ◽  
Jan Wissink ◽  
Wolfgang Rodi
Keyword(s):  
Numerical Simulation ◽  
Boundary Layer ◽  
Direct Numerical Simulation ◽  
Pressure Gradient ◽  
Surface Boundary ◽  
Mean Flow ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Free Stream Turbulence ◽  
Linear Compressor Cascade

Direct Numerical Simulation (DNS) of flow through a linear compressor cascade with incoming free-stream turbulence was performed. On the pressure side, the boundary layer flow is found to undergo by-pass transition: The incident vortical disturbances trigger the formation of elongated boundary layer perturbation jets (or streaks) with amplitudes on the order of 10% of the mean flow. The inception of turbulent spots, which leads to breakdown, is triggered on the backward perturbation jets (negative u-fluctuations). The turbulent patches spread and finally merge into the downstream, fully turbulent region. The suction surface boundary layer is initially subject to a Favorable Pressure Gradient (FPG), followed by a strong Adverse Pressure Gradient (APG). The FPG suppresses the formation of boundary layer streaks. The result is a stabilized boundary layer that does not undergo transition. Farther downstream, the strong APG causes the laminar boundary layer to separate, which is followed by turbulent reattachment.

scholarly journals Direct numerical simulation of hypersonic boundary layer transition over a lifting-body model HyTRV

2021 ◽  
Vol 3 (1) ◽  
Author(s):  
Han Qi ◽  
Xinliang Li ◽  
Changping Yu ◽  
Fulin Tong
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Free Stream ◽  
Central Area ◽  
Lower Surface ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Body Model ◽  
Grid Convergence ◽  
Pod Analysis

AbstractDirect numerical simulation (DNS) of transition over a hypersonic lifting body model HyTRV developed by China Aerodynamics Research and Development Center is performed. The free-stream parameters are: the free-stream Mach number is 6, the unit Reynolds number is 10000/mm, the free-stream temperature is 79 K, the angle of attack is 0, and the wall temperature is 300 K. Weak random blowing-and-suction perturbations in the leading range are used to trigger the transition. A high order finite-difference code OpenCFD developed by the authors is used for the simulation, and grid convergence test shows that the transition locations are grid-convergence. DNS results show that transition occurs in central area of the lower surface and the concaved region of the upper surface, and the transition regions are also the streamline convergence regions. The transition mechanisms in different regions are investigated by using the spectrum and POD analysis.

scholarly journals Combined free-stream disturbance measurements and receptivity studies in hypersonic wind tunnels by means of a slender wedge probe and direct numerical simulation

2018 ◽  
Vol 842 ◽  
pp. 495-531 ◽  
Author(s):  
Alexander Wagner ◽  
Erich Schülein ◽  
René Petervari ◽  
Klaus Hannemann ◽  
Syed R. C. Ali ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Acoustic Wave ◽  
Direct Numerical Simulation ◽  
Acoustic Waves ◽  
Free Stream ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Wind Tunnels ◽  
Wide Range

Combined free-stream disturbance measurements and receptivity studies in hypersonic wind tunnels were conducted by means of a slender wedge probe and direct numerical simulation. The study comprises comparative tunnel noise measurements at Mach 3, 6 and 7.4 in two Ludwieg tube facilities and a shock tunnel. Surface pressure fluctuations were measured over a wide range of frequencies and test conditions including harsh test environments not accessible to measurement techniques such as Pitot probes and hot-wire anemometry. A good agreement was found between normalized Pitot pressure fluctuations converted into normalized static pressure fluctuations and the wedge probe readings. Quantitative results of the tunnel noise are provided in frequency ranges relevant for hypersonic boundary-layer transition. Complementary numerical simulations of the leading-edge receptivity to fast and slow acoustic waves were performed for the applied wedge probe at conditions corresponding to the experimental free-stream conditions. The receptivity to fast acoustic waves was found to be characterized by an early amplification of the induced fast mode. For slow acoustic waves an initial decay was found close to the leading edge. At all Mach numbers, and for all considered frequencies, the leading-edge receptivity to fast acoustic waves was found to be higher than the receptivity to slow acoustic waves. Further, the effect of inclination angles of the acoustic wave with respect to the flow direction was investigated. An inclination angle was found to increase the response on the wave-facing surface of the probe and decrease the response on the opposite surface for fast acoustic waves. A frequency-dependent response was found for slow acoustic waves. The combined numerical and experimental approach in the present study confirmed the previous suggestion that the slow acoustic wave is the dominant acoustic mode in noisy hypersonic wind tunnels.

Sign in / Sign up

Export Citation Format

Share Document