scholarly journals Transitional shock-wave/boundary-layer interactions in hypersonic flow

2014 ◽  
Vol 752 ◽  
pp. 349-382 ◽  
Author(s):  
N. D. Sandham ◽  
E. Schülein ◽  
A. Wagner ◽  
S. Willems ◽  
J. Steelant
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Pressure Sensors ◽  
Transition Process ◽  
Strong Interactions ◽  
Present Contribution ◽  
High Enthalpy ◽  
Reflected Shock ◽  
Ludwieg Tube ◽  
Streamwise Streaks

AbstractStrong interactions of shock waves with boundary layers lead to flow separations and enhanced heat transfer rates. When the approaching boundary layer is hypersonic and transitional the problem is particularly challenging and more reliable data is required in order to assess changes in the flow and the surface heat transfer, and to develop simplified models. The present contribution compares results for transitional interactions on a flat plate at Mach 6 from three different experimental facilities using the same instrumented plate insert. The facilities consist of a Ludwieg tube (RWG), an open-jet wind tunnel (H2K) and a high-enthalpy free-piston-driven reflected shock tunnel (HEG). The experimental measurements include shadowgraph and infrared thermography as well as heat transfer and pressure sensors. Direct numerical simulations (DNS) are carried out to compare with selected experimental flow conditions. The combined approach allows an assessment of the effects of unit Reynolds number, disturbance amplitude, shock impingement location and wall cooling. Measures of intermittency are proposed based on wall heat flux, allowing the peak Stanton number in the reattachment regime to be mapped over a range of intermittency states of the approaching boundary layer, with higher overshoots found for transitional interactions compared with fully turbulent interactions. The transition process is found to develop from second (Mack) mode instabilities superimposed on streamwise streaks.

Transition of streamwise streaks in zero-pressure-gradient boundary layers

2002 ◽  
Vol 472 ◽  
pp. 229-261 ◽  
Author(s):  
LUCA BRANDT ◽  
DAN S. HENNINGSON
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
High Speed ◽  
Plate Boundary ◽  
Transition Process ◽  
Free Stream Turbulence ◽  
Tollmien Schlichting ◽  
Streamwise Streaks ◽  
The Stability ◽  
Optimal Disturbances

A transition scenario initiated by streamwise low- and high-speed streaks in a flat-plate boundary layer is studied. In many shear flows, the perturbations that show the highest potential for transient energy amplification consist of streamwise-aligned vortices. Due to the lift-up mechanism these optimal disturbances lead to elongated streamwise streaks downstream, with significant spanwise modulation. In a previous investigation (Andersson et al. 2001), the stability of these streaks in a zero-pressure-gradient boundary layer was studied by means of Floquet theory and numerical simulations. The sinuous instability mode was found to be the most dangerous disturbance. We present here the first simulation of the breakdown to turbulence originating from the sinuous instability of streamwise streaks. The main structures observed during the transition process consist of elongated quasi-streamwise vortices located on the flanks of the low-speed streak. Vortices of alternating sign are overlapping in the streamwise direction in a staggered pattern. The present scenario is compared with transition initiated by Tollmien–Schlichting waves and their secondary instability and by-pass transition initiated by a pair of oblique waves. The relevance of this scenario to transition induced by free-stream turbulence is also discussed.

Effect of Surface Roughness on Conjugate Heat Transfer of a Turbine Vane

2016 ◽  
Author(s):  
Hongyang Li ◽  
Yun Zheng
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Surface Roughness ◽  
Suction Side ◽  
Transition Process ◽  
Considerable Effect ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Turbine Vane ◽  
Effect Of Surface

For the purpose of researching the effect of surface roughness on boundary layer transition and heat transfer of turbine blade, a roughness modification approach for γ-Reθ transition model was proposed based on an in-house CFD code. Taking surface roughness effect into consideration, No. 5411 working condition of Mark II turbine vane was simulated and the results were analyzed in detail. Main conclusions are as follows: Surface roughness has little effect on heat transfer of laminar boundary layer, while has considerable effect on turbulent boundary layer. Compared with smooth surface, equivalent sand roughness of 100μm increases the temperature for about 28.4K on suction side, reaching an increase of 5%. Under low roughness degree, effect of shock wave dominants on boundary layer transition process on suction side, while above the critical degree, effect of surface roughness could abruptly change the transition point.

Coupled Heat Transfer Simulations of Air-Cooled Turbines with an Algebraic Transition Model

2012 ◽  
Vol 455-456 ◽  
pp. 1153-1159
Author(s):  
Qiang Wang ◽  
Zhao Yuan Guo ◽  
Guo Tai Feng
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Thermal Load ◽  
Transition Process ◽  
Test Case ◽  
Transition Model ◽  
High Pressure Turbine ◽  
Coupled Heat Transfer ◽  
Turbulent Transition ◽  
Turbine Vane

The investigation was to study the effect of laminar-turbulent transition on predicting thermal load of vane. The Abu-Ghannam and Shaw (AGS) algebraic transition model was applied in the coupled solver, HIT3D. Then the solver was employed to carry out coupled heat transfer simulations, and the test case was 5411 run of NASA0-MARKⅡ vane, a high-pressure turbine vane. The results shown that AGS model was able to predict the transition process in the boundary layer near the vane, and that the simulation with such model leads to thermal load agreeing well the measured one. Then the developed solver was applied to predict a low-pressure vane, and the results shown that CHT simulation with full turbulence model would predict higher thermal load than that with transition model.

scholarly journals Low-order stochastic modelling of low-frequency motions in reflected shock-wave/boundary-layer interactions

2011 ◽  
Vol 671 ◽  
pp. 417-465 ◽  
Author(s):  
EMILE TOUBER ◽  
NEIL D. SANDHAM
Keyword(s):  
Boundary Layer ◽  
Low Frequency ◽  
Intrinsic Property ◽  
Stochastic Modelling ◽  
Reflected Shock Wave ◽  
Present Contribution ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Reflected Shock ◽  
Wide Range

A combined numerical and analytical approach is used to study the low-frequency shock motions observed in shock/turbulent-boundary-layer interactions in the particular case of a shock-reflection configuration. Starting from an exact form of the momentum integral equation and guided by data from large-eddy simulations, a stochastic ordinary differential equation for the reflected-shock-foot low-frequency motions is derived. During the derivation a similarity hypothesis is verified for the streamwise evolution of boundary-layer thickness measures in the interaction zone. In its simplest form, the derived governing equation is mathematically equivalent to that postulated without proof by Plotkin (AIAA J., vol. 13, 1975, p. 1036). In the present contribution, all the terms in the equation are modelled, leading to a closed form of the system, which is then applied to a wide range of input parameters. The resulting map of the most energetic low-frequency motions is presented. It is found that while the mean boundary-layer properties are important in controlling the interaction size, they do not contribute significantly to the dynamics. Moreover, the frequency of the most energetic fluctuations is shown to be a robust feature, in agreement with earlier experimental observations. The model is proved capable of reproducing available low-frequency experimental and numerical wall-pressure spectra. The coupling between the shock and the boundary layer is found to be mathematically equivalent to a first-order low-pass filter. It is argued that the observed low-frequency unsteadiness in such interactions is not necessarily a property of the forcing, either from upstream or downstream of the shock, but an intrinsic property of the coupled system, whose response to white-noise forcing is in excellent agreement with actual spectra.

Numerical Simulation of Turbulent Impingement Cooling

2001 ◽  
Author(s):  
Andreas Abdon ◽  
Bengt Sundén
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulence Models ◽  
Local Heat Transfer ◽  
Transition Process ◽  
Local Heat ◽  
Boundary Layer Transition ◽  
Wall Jet ◽  
Layer Transition ◽  
Stagnation Region

Simulations of turbulent impinging jet heat transfer for different nozzle configurations using Reynolds averaged governing equations and two-equation turbulence models have been conducted. The considered nozzle configurations are a square-edged orifice and a pipe exit. The results for a jet Reynolds number of 10000 and dimensionless nozzle-to-plate distance of 2 show that the heat transfer is well predicted for the pipe configuration but underpredicted for the orifice. The disagreement may be partly explained by underprediction of turbulence in the stagnation region and inaccurate treatment of the wall jet boundary layer transition. An investigation of the local heat transfer distribution for the orifice reveals two local maxima. These are related to an accelerating laminar boundary layer and the transition process of the wall jet, respectively, for the calculations. The application of a realizability constraint on the models leads to reduced turbulence levels, not only in the stagnation region, but also in the throttled flow of the orifice configuration. This improves the prediction of heat transfer and nozzle exit turbulence levels significantly.

Nonlinear instability of developing streamwise vortices with applications to boundary layer heat transfer intensification through an extended Reynolds analogy

2008 ◽  
Vol 366 (1876) ◽  
pp. 2699-2716 ◽  
Author(s):  
J.T.C Liu
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Flux ◽  
Reynolds Shear Stress ◽  
Streamwise Vortex ◽  
Secondary Instability ◽  
Streamwise Vortices ◽  
Present Contribution ◽  
Reynolds Analogy ◽  
Transport Effects

The intent of the present contribution is to explain theoretically the experimentally measured surface heat transfer rates on a slightly concave surface with a thin boundary layer in an otherwise laminar flow. As the flow develops downstream, the measured heat transfer rate deviates from the local laminar value and eventually exceeds the local turbulent value in a non-trivial manner even in the absence of turbulence. While the theory for steady strong nonlinear development of streamwise vortices can bridge the heat transfer from laminar to the local turbulent value, further intensification is attributable to the transport effects of instability of the basic steady streamwise vortex system. The problem of heat transport by steady and fluctuating nonlinear secondary instability is formulated. An extended Reynolds analogy for Prandtl number unity, Pr =1, is developed, showing the similarity between streamwise velocity and the temperature. The role played by the fluctuation-induced heat flux is similar to momentum flux by the Reynolds shear stress. Inferences from the momentum problem indicate that the intensified heat flux developing well beyond the local turbulent value is attributed to the transport effects of the nonlinear secondary instability, which leads to the formation of ‘coherent structures’ of the flow. The basic underlying pinions of the non-linear hydrodynamic stability problem are the analyses of J. T. Stuart, which uncovered physical mechanisms of nonlinearities that are crucial to the present developing boundary layers supporting streamwise vortices and their efficient scalar transporting mechanisms.

scholarly journals Effects of Leading-Edge Roughness on Fluid Flow and Heat Transfer in the Transitional Boundary Layer Over a Flat Plate

1994 ◽  
Author(s):  
Mark Pinson ◽  
Ting Wang
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Free Stream ◽  
Turbine Blades ◽  
Leading Edge ◽  
Transition Process ◽  
Stanton Number ◽  
Edge Roughness ◽  
Wide Range ◽  
Edge Conditions

An experimental study was undertaken to gain insight into the physical mechanisms that affect the laminar-turbulent transition process downstream of the leading-edge roughness condition. Three sizes of sandpaper strips were chosen to simulate the randomly distributed roughness located near the leading edge of a turbine blade, and three sizes of cylinders were chosen to simulate the relatively isolated peak nature of the roughness structure. The roughness Reynolds numbers tested covered a wide range, from 2 to 2840. The roughness sizes were selected based on the measured roughness characteristics of used gas turbine blades. The results indicated that at low free-stream velocities (5 m/s), the maximum roughness height was the primary contributor to deviations from the undisturbed case. At higher free-stream velocities (5–7 m/s), three of the rough leading-edge conditions exhibited a dual-slope region between the laminar and turbulent Stanton number versus Reynolds number correlations. Analysis of the boundary layer indicated that the first segment of the dual-slope was laminar, but the wall heat transfer significantly deviates from the laminar correlation. The second segment was transitional. The dual-slope behavior and the waviness of the Stanton number distribution at higher free-stream velocities observed downstream of the rough leading-edge conditions are believed to have been caused by nonlinear amplification introduced by the finite disturbances at the leading edge.

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