Theoretical Analysis of the Effect of Compressibility and Free-Stream Turbulence on Free-Mixing Turbulent Gas Flows

1976 ◽  
Vol 43 (2) ◽  
pp. 217-221
Author(s):  
B. K. Shivamoggi
Keyword(s):  
High Speed ◽  
Free Stream ◽  
Mixing Layer ◽  
Gas Flows ◽  
Flow Equations ◽  
Free Stream Turbulence ◽  
Gas Streams ◽  
Layer Flow ◽  
Flow Similarity ◽  
Compressibility Effects

A theoretical investigation is made of the effect of compressibility and free-stream turbulence on the mixing-layer flow between high-speed parallel turbulent gas streams. Compressibility effects on turbulence are formulated through suitable phenomenological models. The flow similarity principle is then invoked to analyze the flow equations; the results of which directly reveal the manner in which the compressibility effects and the free-stream turbulence affect the development of the mixing flow.

Heat Transfer in Separated Flows at High Levels of Free-Stream Turbulence

2010 ◽  
Author(s):  
V. I. Terekhov ◽  
N. I. Yarygina
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Mixing Layer ◽  
Cross Flow ◽  
Thermal Characteristics ◽  
Separated Flow ◽  
Separated Flows ◽  
Transfer Coefficients ◽  
Free Stream Turbulence ◽  
Layer Flow

In the present paper, a comparative analysis of the influence of free-stream turbulence on the separated flows past obstacles is given. As the obstacles, a downward-facing step, a flat rib installed at different orientations to the free-stream direction, a system of several ribs, and a cross-flow trench with vertical or inclined walls are considered. The experimental results obtained in the present study are compared to data previously reported by other workers. The structure of the separated flow at an enhanced level of free-stream turbulence is compared to the flow under low-turbulence conditions in terms of the characteristic length of the separation zone, mixing-layer parameters, and pressure distributions. The emphasis is on the thermal characteristics, including the profiles of temperature across the shear layer, the distributions of temperature over the streamlined surface, and the local and mean heat-transfer coefficients. It is shown that the effect of enhanced free-stream turbulence on the separated flow is much more pronounced than that on the boundary-layer flow over a flat surface. For separated flow, this effect is manifested more clearly behind rib than behind step. The largest heat-transfer intensification ratios due to external turbulence were found in the cross-flow trench and in the system of ribs.

Influence of Free-Stream Turbulence on Turbulent Boundary Layer Heat Transfer and Mean Profile Development, Part I—Experimental Data

1983 ◽  
Vol 105 (1) ◽  
pp. 33-40 ◽  
Author(s):  
M. F. Blair
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Boundary Layer Flow ◽  
Free Stream ◽  
Full Range ◽  
Stream Velocity ◽  
Free Stream Turbulence ◽  
Turbulent Boundary Layer Flow ◽  
Layer Flow

An experimental research program was conducted to determine the influence of free-stream turbulence on zero pressure gradient, fully turbulent boundary layer flow. Connective heat transfer coefficients and boundary layer mean velocity and temperature profile data were obtained for a constant free-stream velocity of 30 m/s and free-stream turbulence intensities ranging from approximately 1/4 to 7 percent. Free-stream multicomponent turbulence intensity, longitudinal integral scale, and spectral distributions were obtained for the full range of turbulence levels. The test results with 1/4 percent free-stream turbulence indicate that these data were in excellent agreement with classic two-dimensional, low free-stream turbulence, turbulent boundary layer correlations. For fully turbulent boundary layer flow, both the skin friction and heat transfer were found to be substantially increased (up to ∼ 20 percent) for the higher levels of free-stream turbulence. Detailed results of the experimental study are presented in the present paper (Part I). A comprehensive analysis is provided in a companion paper (Part II).

Toward second-moment closure modelling of compressible shear flows

2013 ◽  
Vol 733 ◽  
pp. 325-369 ◽  
Author(s):  
Carlos A. Gomez ◽  
Sharath S. Girimaji
Keyword(s):  
High Speed ◽  
Evolution Equations ◽  
Thermal Flux ◽  
Mixing Layer ◽  
Layer Growth ◽  
Moment Closure ◽  
Unified Framework ◽  
Second Moment Closure ◽  
Closure Modelling ◽  
Compressibility Effects

AbstractCompressibility profoundly affects many aspects of turbulence in high-speed flows, most notably stability characteristics, anisotropy, kinetic–potential energy interchange and spectral cascade rate. We develop a unified framework for modelling pressure-related compressibility effects by characterizing the role and action of pressure in different speed regimes. Rapid distortion theory is used to examine the physical connection between the various compressibility effects leading to model form suggestions for pressure–strain correlation, pressure–dilatation and dissipation evolution equations. The closure coefficients are established using fixed-point analysis by requiring consistency between model and DNS asymptotic behaviour in compressible homogeneous shear flow. The closure models are employed to compute high-speed mixing layers and boundary layers. The self-similar mixing-layer profile, increased Reynolds stress anisotropy and diminished mixing-layer growth rates with increasing Mach number are all well captured. High-speed boundary-layer results are also adequately replicated even without the use of advanced thermal-flux models or low-Reynolds-number corrections.

Boundary-Layer Transition and Separation Near the Leading Edge of a High-Speed Turbine Blade

1985 ◽  
Vol 107 (1) ◽  
pp. 127-134 ◽  
Author(s):  
H. P. Hodson
Keyword(s):  
Boundary Layers ◽  
Turbine Blade ◽  
High Speed ◽  
Free Stream ◽  
Leading Edge ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Initial Development ◽  
Free Stream Turbulence ◽  
Hot Film

The state of the boundary layers near the leading edge of a high-speed turbine blade has been investigated, in cascade, using an array of surface-mounted, constant-temperature, hot-film anemometers. The measurements are interpreted with the aid of inviscid and viscous prediction codes. The effects of Reynolds number, compressibility, incidence, and free-stream turbulence are described. In all cases, the initial development of the boundary layers was extremely complex and, even at design conditions, separation and reattachment, transition and relaminarization were found to occur.

Importance of Boundary Layer Transition in a High-Pressure Turbine Cascade Using LES

2018 ◽  
Author(s):  
Luis M. Seguí ◽  
L. Y. M. Gicquel ◽  
F. Duchaine ◽  
J. de Laborderie
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Flux ◽  
Free Stream ◽  
Industrial Process ◽  
Great Difficulty ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Layer Flow

In the context of smooth surfaces where no industrial process modifies the flow and where no roughness affects the boundary layer flow, there are configurations today where the correct heat flux prediction is still unattained for certain operating points. This is the case of the LS89 configuration that has shown to be of great difficulty to accurately simulate the thermal fields for high Reynolds number flows even when performing wall-resolved Large Eddy Simulations (LES). The physics of the studied operating point (MUR235) are especially complex due to the interaction of a transitioning boundary layer, shock waves and free-stream turbulence injected at the inlet. In this paper, free-stream turbulent specifications are seen to be important towards the capture of the heat transfer profile on most regions of the blade. The boundary layer is found to be transitional when either artificially raising the level of turbulence at the inlet or by using a highly refined mesh that induces the generation of turbulent spots that increase the heat transfer. The important refinement done improves the heat flux predictions to the point it is approaching the experimental data.

Receptivity mechanisms in three-dimensional boundary-layer flows

2009 ◽  
Vol 618 ◽  
pp. 209-241 ◽  
Author(s):  
LARS-UVE SCHRADER ◽  
LUCA BRANDT ◽  
DAN S. HENNINGSON
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Three Dimensional ◽  
Leading Edge ◽  
Nonlinear Process ◽  
Transition To Turbulence ◽  
Boundary Layer Flows ◽  
Free Stream Turbulence ◽  
Dimensional Boundary ◽  
Layer Flow

Receptivity in three-dimensional boundary-layer flow to localized surface roughness and free-stream vorticity is studied. A boundary layer of Falkner–Skan–Cooke type with favourable pressure gradient is considered to model the flow slightly downstream of a swept-wing leading edge. In this region, stationary and travelling crossflow instability dominates over other instability types. Three scenarios are investigated: the presence of low-amplitude chordwise localized, spanwise periodic roughness elements on the plate, the impingement of a weak vortical free-stream mode on the boundary layer and the combination of both disturbance sources. Three receptivity mechanisms are identified: steady receptivity to roughness, unsteady receptivity to free-stream vorticity and unsteady receptivity to vortical modes scattered at the roughness. Both roughness and vortical modes provide efficient direct receptivity mechanisms for stationary and travelling crossflow instabilities. We find that stationary crossflow modes dominate for free-stream turbulence below a level of about 0.5%, whereas higher turbulence levels will promote the unsteady receptivity mechanism. Under the assumption of small amplitudes of the roughness and the free-stream disturbance, the unsteady receptivity process due to scattering of free-stream vorticity at the roughness has been found to give small initial disturbance amplitudes in comparison to the direct mechanism for free-stream modes. However, in many environments free-stream vorticity and roughness may excite interacting unstable stationary and travelling crossflow waves. This nonlinear process may rapidly lead to large disturbance amplitudes and promote transition to turbulence.

A method for solving compressible flow equations in an unsteady free stream

2006 ◽  
Vol 220 (2) ◽  
pp. 185-202 ◽  
Author(s):  
S A Karabasov ◽  
T P Hynes
Keyword(s):  
High Speed ◽  
Free Stream ◽  
Model Problem ◽  
Domain Boundary ◽  
Open Domain ◽  
Computational Accuracy ◽  
Flow Solver ◽  
Flow Equations ◽  
Helicopter Blades ◽  
Additional Constraints

The paper presents a method to increase the computational accuracy by preserving additional constraints on the numerical solution. The new technique can noticeably increase the precision of a standard finite-volume flow solver by a modification to the flux computation procedure without changing its essential features. The efficiency of this method is demonstrated by application to the prediction of sound from high-speed helicopter blades. Several open domain boundary conditions for this application are also developed and compared for a model problem of a two-dimensional transonic aerofoil in an unsteady free stream.

scholarly journals Transition in an infinite swept-wing boundary layer subject to surface roughness and free-stream turbulence

2021 ◽  
Vol 931 ◽  
Author(s):  
Luca De Vincentiis ◽  
Dan S. Henningson ◽  
Ardeshir Hanifi
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Flow Instability ◽  
Transition To Turbulence ◽  
Computational Domain ◽  
Swept Wing ◽  
Free Stream Turbulence ◽  
Roughness Elements ◽  
Layer Flow ◽  
Institute Of Technology

The instability of an incompressible boundary-layer flow over an infinite swept wing in the presence of disc-type roughness elements and free-stream turbulence (FST) has been investigated by means of direct numerical simulations. Our study corresponds to the experiments by Örlü et al. (Tech. Rep., KTH Royal Institute of Technology, 2021, http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-291874). Here, different dimensions of the roughness elements and levels of FST have been considered. The aim of the present work is to investigate the experimentally observed sensitivity of the transition to the FST intensity. In the absence of FST, flow behind the roughness elements with a height above a certain value immediately undergoes transition to turbulence. Impulse–response analyses of the steady flow have been performed to identify the mechanism behind the observed flow instability. For subcritical roughness, the generated wave packet experiences a weak transient growth behind the roughness and then its amplitude decays as it is advected out of the computational domain. In the supercritical case, in which the flow transitions to turbulence, flow as expected exhibits an absolute instability. The presence of FST is found to have a significant impact on the transition behind the roughness, in particular in the case of a subcritical roughness height. For a height corresponding to a roughness Reynolds number $Re_{hh}=461$ , in the absence of FST the flow reaches a steady laminar state, while a very low FST intensity of $Tu =0.03\,\%$ causes the appearance of turbulence spots in the wake of the roughness. These randomly generated spots are advected out of the computational domain. For a higher FST level of $Tu=0.3\,\%$ , a turbulent wake is clearly visible behind the element, similar to that for the globally unstable case. The presented results confirm the experimental observations and explain the mechanisms behind the observed laminar–turbulent transition and its sensitivity to FST.

Effect of free-stream turbulence on large structure in turbulent mixing layers

1978 ◽  
Vol 85 (4) ◽  
pp. 693-704 ◽  
Author(s):  
C. Chandrsuda ◽  
R. D. Mehta ◽  
A. D. Weir ◽  
P. Bradshaw
Keyword(s):  
Turbulent Mixing ◽  
Bluff Body ◽  
Free Stream ◽  
Early Stage ◽  
Mixing Layer ◽  
Three Dimensional ◽  
Large Structure ◽  
Free Stream Turbulence ◽  
Instability Modes ◽  
Slow Development

Flow-visualization investigations and correlation measurements show that the essentially two-dimensional structures which dominated the turbulent mixing layer of Brown & Roshko (1974) are formed only if the free-stream turbulence is low. If free-stream disturbances are significant, as is likely in most practical cases, including a mixing layer entraining ‘still air’ from the surroundings, three-dimensionality develops at an early stage in transition. Other recent experiments strongly suggest that the Brown-Roshko structure will not form if the initial mixing layer is turbulent or subject to instability modes other than spanwise vortices. Therefore the Brown-Roshko structure will be rare in practice. The alternative large structure in a mixing layer, found by several workers, is intense, but fully three-dimensional and thus less orderly than the Brown-Roshko structure.The balance of evidence suggests that if the Brown-Roshko structure does appear it will eventually relax into the alternative fully three-dimensional form: the Kármán vortex street behind a bluff body provides a precedent for slow development of three-dimensionality. However the Brown-Roshko structure, if formed, may well relax so slowly as to be identifiable for the full length of a practical flow.

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