Investigation of the effect of the wall roughness and free stream turbulence on the boundary layer development

The influence of turbulence on the flow around a wall-mounted cube immersed in a turbulent boundary layer is investigated experimentally with particle image velocimetry and hot-wire anemometry. Free-stream turbulence is used to generate turbulent boundary layer profiles where the normalised shear at the cube height is fixed, but the turbulence intensity at the cube height is adjustable. The free-stream turbulence is generated with an active grid and the turbulent boundary layer is formed on an artificial floor in a wind tunnel. The boundary layer development Reynolds number ($Re_{x}$) and the ratio of the cube height ($h$) to the boundary layer thickness ($\unicode[STIX]{x1D6FF}$) are held constant at $Re_{x}=1.8\times 10^{6}$ and $h/\unicode[STIX]{x1D6FF}=0.47$. It is demonstrated that the stagnation point on the upstream side of the cube and the reattachment length in the wake of the cube are independent of the incoming profile for the conditions investigated here. In contrast, the wake length monotonically decreases for increasing turbulence intensity but fixed normalised shear – both quantities measured at the cube height. The wake shortening is a result of heightened turbulence levels promoting wake recovery from high local velocities and the reduction in strength of a dominant shedding frequency.

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Free-Stream Turbulence and Pressure Gradient Effects on Heat Transfer and Boundary Layer Development on Highly Cooled Surfaces

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.3239697 ◽

1985 ◽

Vol 107 (1) ◽

pp. 54-59 ◽

Cited By ~ 6

Author(s):

K. Rued ◽

S. Wittig

Keyword(s):

Heat Transfer ◽

Boundary Layer ◽

Free Stream ◽

Boundary Layer Transition ◽

Pressure Gradients ◽

Layer Transition ◽

Free Stream Turbulence ◽

Boundary Layer Development ◽

Gradient Effects ◽

Layer Development

Heat transfer and boundary layer measurements were derived from flows over a cooled flat plate with various free-stream turbulence intensities (Tu = 1.6–11 percent), favorable pressure gradients (k = νe/ue2•due/dx = 0÷6•10−6) and cooling intensities (Tw/Te = 1.0–0.53). Special interest is directed towards the effects of the dominant parameters, including the influence on laminar to turbulent boundary layer transition. It is shown, that free-stream turbulence and pressure gradients are of primary importance. The increase of heat transfer due to wall cooling can be explained primarily by property variations as transition, and the influence of free-stream parameters are not affected.

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The Development of the Profile Boundary Layer in a Turbine Environment

Volume 1: Turbomachinery ◽

10.1115/86-gt-244 ◽

1986 ◽

Cited By ~ 1

Author(s):

J. Hourmouziadis ◽

F. Buckl ◽

P. Bergmann

Keyword(s):

Boundary Layer ◽

Free Stream ◽

Rotor Blades ◽

Turbulence Structure ◽

Test Results ◽

Free Stream Turbulence ◽

Boundary Layer Development ◽

Wake Effects ◽

Actual Flow ◽

Layer Development

Cascade testing tries to simulate the actual flow conditions encountered in a turbine. However, it is neither possible to reproduce the free stream turbulence structure of the turbomachinery, nor the periodic wake effects of upstream blade rows. The usual understanding is that the latter in particular results in a significantly different behaviour of the boundary layer in the engine. Experimental results from cascades and turbine rigs are presented. Grid generated free stream turbulence structure is compared to that in the turbine. Measurements of the profile pressure distribution, flush mounted hot films and flow visualization were used for the interpretation of the test results. Some observations of the boundary layer development in the cascade, on the guide vanes and on rotor blades with typically skewed boundary layers are shown indicating essentially similar behaviour in all cases.

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The Development of the Profile Boundary Layer in a Turbine Environment

Journal of Turbomachinery ◽

10.1115/1.3262101 ◽

1987 ◽

Vol 109 (2) ◽

pp. 286-295 ◽

Cited By ~ 5

Author(s):

J. Hourmouziadis ◽

F. Buckl ◽

P. Bergmann

Keyword(s):

Boundary Layer ◽

Free Stream ◽

Rotor Blades ◽

Turbulence Structure ◽

Test Results ◽

Free Stream Turbulence ◽

Boundary Layer Development ◽

Wake Effects ◽

Actual Flow ◽

Layer Development

Cascade testing tries to simulate the actual flow conditions encountered in a turbine. However, it is possible to reproduce neither the free-stream turbulence structure of the turbomachinery, nor the periodic wake effects of upstream blade rows. The usual understanding is that the latter in particular results in a significantly different behavior of the boundary layer in the engine. Experimental results from cascades and turbine rigs are presented. Grid-generated free-stream turbulence structure is compared to that in the turbine. Measurements of the profile pressure distribution, flush-mounted hot films, and flow visualization were used for the interpretation of the test results. Some observations of the boundary layer development in the cascade, on the guide vanes, and on rotor blades with typically skewed boundary layers are shown indicating essentially similar behavior in all cases.

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Time Scales for Unsteady Mass Transfer From a Sphere at Low-Finite Reynolds Numbers

Journal of Heat Transfer ◽

10.1115/1.1576813 ◽

2003 ◽

Vol 125 (4) ◽

pp. 716-723 ◽

Cited By ~ 5

Author(s):

Stanley J. Kleis ◽

Ivan Rivera-Solorio

Keyword(s):

Boundary Layer ◽

Mass Transfer ◽

Flow Field ◽

Time Scales ◽

Free Stream ◽

Reynolds Numbers ◽

Concentration Boundary Layer ◽

Concentration Boundary ◽

Boundary Layer Development ◽

Layer Development

The problem of unsteady mass transfer from a sphere that impulsively moves from rest to a finite velocity in a non-uniform concentration distribution is studied. A range of low Reynolds numbers (Re<1) and moderate Peclet numbers (Pe ranges from 5.6 to 300) is investigated (typical of the parameters encountered in anchorage dependent cell cultures in micro gravity). Using time scales, the effects of flow field development, concentration boundary layer development and free stream concentration variation are investigated. For the range of parameters considered, the development of the flow field has a negligible effect on the time variation of the Sherwood number (Sh). The Sh time dependence is dominated by concentration boundary layer development for early times and free stream concentration variations at later times.

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The Influence of Tip Clearance, Stage Loading, and Wall Roughness on Compressor Casing Boundary Layer Development

Volume 1: Turbomachinery ◽

10.1115/82-gt-153 ◽

1982 ◽

Author(s):

J. L. Bettner ◽

C. Elrod

Keyword(s):

Boundary Layer ◽

Layer Growth ◽

Tip Clearance ◽

Experimental Program ◽

Wall Roughness ◽

Stall Margin ◽

Boundary Layer Development ◽

Blade Tip ◽

Boundary Layer Growth ◽

Layer Development

An experimental program was conducted in a highly loaded, single-stage, low-speed research compressor that featured variations in blade tip clearances, shroud wall roughness, and stage loading levels. The results showed that tip clearances and stage loading levels exerted a very strong influence on casing boundary layer growth. Shroud wall roughness not only showed some effect on casing boundary layer development, but also influenced stage stall margin. The results point out the need to understand the basic flow processes that occur if realistic mathematical models are to be developed so that casing boundary layer development and its influence on compressor stage performance can be accurately predicted.

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