Heat Transfer Visualization and Measurement in Unstable Concave-Wall Laminar Boundary Layers

1989 ◽  
Vol 111 (1) ◽  
pp. 51-56 ◽  
Author(s):  
R. I. Crane ◽  
J. Sabzvari
Keyword(s):  
Heat Transfer ◽  
Boundary Layers ◽  
Constant Heat Flux ◽  
Contributory Factor ◽  
Constant Wall Temperature ◽  
Pressure Surface ◽  
Laminar Boundary Layers ◽  
Concave Wall ◽  
Temperature Constant ◽  
Intermittency Factor

Using liquid crystal sheet in a hybrid constant-wall-temperature/constant-heat-flux procedure, heat transfer distributions have been measured in concave-wall laminar boundary layers with a natural Gortler vortex system in a near-zero pressure gradient. Stanton numbers at vortex downwash positions across the span exceeded those at upwash positions by factors as high as three. Spanwise-averaged Stanton numbers exceeded analytical flat-plate values only after the appearance of highly inflected upwash velocity profiles and the onset of span wise meandering of the vortices, where the Gortler number exceeded ten. Levels then reached values comparable with turbulent correlations, at Reynolds numbers and turbulence levels (up to 3 percent) where previous measurements of the intermittency factor indicated that transition had not begun. Boundary layer thinning in downwash zones could account for much of the heat transfer enhancement. The phenomenon could be a contributory factor to the long, apparently transitional regions often reported on blade cascade pressure surfaces, although the Gortler numbers where enhancement occurred are higher than those normally associated with pressure-surface transition.

Laminar boundary layers behind detonation waves

1983 ◽  
Vol 387 (1793) ◽  
pp. 331-349 ◽  
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Boundary Layers ◽  
Flow Analysis ◽  
Time Dependent ◽  
Detonation Waves ◽  
Planar Geometry ◽  
Laminar Boundary Layers ◽  
Spherical Detonation ◽  
Layer Flow

New solutions are presented for non-stationary boundary layers induced by planar, cylindrical and spherical Chapman-Jouguet (C-J) detonation waves. The numerical results show that the Prandtl number ( Pr ) has a very significant influence on the boundary-layer-flow structure. A comparison with available time-dependent heat-transfer measurements in a planar geometry in a 2H 2 + O 2 mixture shows much better agreement with the present analysis than has been obtained previously by others. This lends confidence to the new results on boundary layers induced by cylindrical and spherical detonation waves. Only the spherical-flow analysis is given here in detail for brevity.

The Effects of Incident Turbulence and Moving Wakes on Laminar Heat Transfer in Gas Turbines

1994 ◽  
Vol 116 (1) ◽  
pp. 23-28 ◽  
Author(s):  
K. Dullenkopf ◽  
R. E. Mayle
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Boundary Layers ◽  
Gas Turbines ◽  
Free Stream ◽  
Turbulence Parameter ◽  
Constant Acceleration ◽  
Free Stream Turbulence ◽  
Laminar Boundary Layers ◽  
Good Agreement

The effect of free-stream turbulence and moving wakes on augmenting heat transfer in accelerating laminar boundary layers is considered. First, the effect of free-stream turbulence is re-examined in terms of a Nusselt number and turbulence parameter, which correctly account for the free-stream acceleration and a correlation for both cylinders in crossflow and airfoils with regions of constant acceleration is obtained. This correlation is then used in a simple quasi-steady model to predict the effect of periodically passing wakes on airfoil laminar heat transfer. A comparison of the predictions with measurements shows good agreement.

The Concept of Adiabatic Heat Transfer Coefficient and its Application to Turbomachinery

2013 ◽  
Author(s):  
Reinaldo A. Gomes ◽  
Reinhard Niehuis
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Boundary Conditions ◽  
Transfer Coefficient ◽  
Constant Heat Flux ◽  
Transfer Coefficients ◽  
Constant Wall Temperature ◽  
Heat Transfer Coefficients ◽  
Thermal Boundary Conditions ◽  
Critical Components

Typical turbomachinery flows are too complex to be predicted by analytical solutions alone. Therefore numerous correlations and test data are used in conjunction with numerical tools in order to design thermally critical components. This approach can be problematic because these correlations and data are not fully independent of the boundary conditions applied. The heat transfer coefficients obtained are not only dependent on the aerodynamics of the flow but also on the thermal boundary layer created along the surface. The adiabatic heat transfer coefficient is the only one which is independent of the thermal boundary conditions, as long as the energy equation can be considered linear with respect to the temperature. However, a proper prediction of the surface temperature cannot be obtained with the adiabatic heat transfer coefficient alone. This paper first reviews the concept of adiabatic heat transfer coefficient and its application to turbomachinery flows. Later, a concept is introduced to allow interchanging between different definitions of heat transfer coefficient and boundary conditions, i.e. constant heat flux or constant wall temperature. Finally, a typical configuration for measuring the adiabatic heat transfer coefficient on a turbine blade and the conversion to other definitions of heat transfer coefficient is presented and evaluated. It is shown that with the technique presented here even small deficiencies of some experiments can be compensated for.

Thermal Radiation in Laminar Boundary Layers on Continuous Moving Surfaces

1974 ◽  
Vol 96 (1) ◽  
pp. 32-36 ◽  
Author(s):  
C. A. Rhodes ◽  
C. C. Chen
Keyword(s):  
Heat Transfer ◽  
Thermal Radiation ◽  
Boundary Layers ◽  
Analytical Study ◽  
Radiation Flux ◽  
Radiation Heat Transfer ◽  
Normal Velocity ◽  
Radiation Heat ◽  
Flat Plates ◽  
Laminar Boundary Layers

Thermal radiation heat transfer is studied in boundary layers on continuous moving surfaces. An analytical study is performed for two-dimensional laminar flow of an absorbing and emitting fluid. Solutions were obtained for limiting conditions of optically thin and thick boundary layers. Comparisons indicate that the radiation flux in these boundary layers is less than that for flow over semi-infinite flat plates for optically thin flows. The radiation contribution becomes more nearly equal as optical thickness increases. The normal velocity induced in the free stream by the wall motion significantly affects the radiation heat transfer.

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