Effects of Free-Stream Turbulence and Wake Characteristics on the Heat Transfer Along a Cooled Gas Turbine Blade

1988 ◽  
Author(s):  
S. Wittig ◽  
A. Schulz ◽  
K. Dullenkopf ◽  
J. Fairbank
Keyword(s):  
Heat Transfer ◽  
Unsteady Flow ◽  
Gas Turbine ◽  
Special Interest ◽  
Free Stream ◽  
Cross Flow ◽  
Wake Flow ◽  
Flow Conditions ◽  
Free Stream Turbulence ◽  
Modeling Concept

Heat transfer measurements under steady, quasi-steady and unsteady flow conditions are discussed. In continuing measurements on the influence of a plane steady wake flow as well as on the effects of grid-produced free-stream turbulence, the present paper describes the effects of the superposition of the free-stream turbulence with the wake flow. Of special interest is a comparison of the wake produced by a leading airfoil with that of a cylindrical bar in cross flow. The similarity of the wakes as far as macrostructure of the turbulence and velocity is concerned is documented using LDV and heat transfer measurements. In extending the modeling concept, a rotating wake generator is employed simulating the wake of a blade with cylindrical bars in cross flow. The comparison of the theoretical and experimental results is presented.

Effusion-Cooling Performance at Gas Turbine Combustor Representative Flow Conditions

2012 ◽  
Author(s):  
Vinod U. Kakade ◽  
Steven J. Thorpe ◽  
Miklós Gerendás
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Free Stream ◽  
Flow Conditions ◽  
Cooling Performance ◽  
Free Stream Turbulence ◽  
High Turbulence ◽  
Adiabatic Effectiveness

The thermal management of aero gas turbine engine combustion systems commonly employs effusion-cooling in combination with various cold-side convective cooling schemes. The combustor liner incorporates many small holes which are usually set in staggered arrays and at a shallow angle to the cooled surface; relatively cold compressor delivery air is then allowed to flow through these holes to provide the full-coverage film-cooling effect. The efficient design of such systems requires robust correlations of film-cooling effectiveness and heat transfer coefficient at a range of aero-thermal conditions, and the use of appropriately validated computational models. However, the flow conditions within a combustor are characterised by particularly high turbulence levels and relatively large length scales. The experimental evidence for performance of effusion-cooling under such flow conditions is currently sparse. The work reported here is aimed at quantifying typical effusion-cooling performance at a range of combustor relevant free-stream conditions (high turbulence), and also to assess the importance of modeling the coolant to free-stream density ratio. Details of a new laboratory wind-tunnel facility for the investigation of film-cooling at high turbulence levels are reported. For a typical combustor effusion geometry that uses cylindrical holes, spatially resolved measurements of adiabatic effectiveness, heat transfer coefficient and net heat flux reduction are presented for a range of blowing ratios (0.48 to 2), free-stream turbulence conditions (4 and 22%) and density ratios (0.97 and 1.47). The measurements reveal that elevated free-stream turbulence impacts on both the adiabatic effectiveness and heat transfer coefficient, although this is dependent upon the blowing ratio being employed and particularly the extent to which the coolant jets detach from the surface. At low blowing ratios the presence of high turbulence levels causes increased lateral spreading of the coolant adjacent to the injection points, but more rapid degradation in the downstream direction. At high blowing ratios, high turbulence levels cause a modest increase in effectiveness due to turbulent transport of the detached coolant fluid. Additionally, the augmentation of heat transfer coefficient caused by the coolant injection is seen to be increased at high free-stream turbulence levels.

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

1992 ◽  
Author(s):  
K. Dullenkopf ◽  
R. E. Mayle
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Gas Turbines ◽  
Free Stream ◽  
Cross Flow ◽  
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 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 cross flow 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.

Direct Numerical Simulations of a Transonic Tip Flow With Free-Stream Disturbances

2013 ◽  
Author(s):  
Andrew P. S. Wheeler ◽  
Richard D. Sandberg
Keyword(s):  
Heat Transfer ◽  
High Performance ◽  
Free Stream ◽  
Separation Bubble ◽  
Cross Flow ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Computational Domain ◽  
Free Stream Turbulence ◽  
Gap Height

In this paper we use direct numerical simulation to investigate the unsteady flow over a model turbine blade-tip at engine scale Reynolds and Mach numbers. The DNS is performed with a new in-house multi-block structured compressible Navier-Stokes solver purposely developed for exploiting high-performance computing systems. The particular case of a transonic tip flow is studied since previous work has suggested compressibility has an important influence on the turbulent nature of the separation bubble at the inlet to the gap and subsequent flow reattachment. The effects of free-stream turbulence, cross-flow and pressure-side boundary-layer on the tip flow aerodynamics and heat transfer are investigated. For ‘clean’ in-flow cases we find that even at engine scale Reynolds numbers the tip flow is intermittent in nature (neither laminar nor fully turbulent). The breakdown to turbulence occurs through the development of spanwise modes with wavelengths around 25% of the gap height. Cross-flows of 25% of the streamwise gap exit velocity are found to increase the stability of the tip flow, and to significantly reduce the turbulence production in the separation bubble. This is predicted through in-house linear stability analysis, and confirmed by the DNS. For the case when the inlet flow has free-stream turbulence, viscous dissipation and the rapid acceleration of the flow at the inlet to the tip-gap causes significant distortion of the vorticity field and reductions of turbulence intensity as the flow enters the tip gap. This means that only very high turbulence levels at the inlet to the computational domain significantly affect the tip heat transfer. The DNS results are compared with RANS predictions using the Spalart-Allmaras and k–ω SST turbulence models. The RANS and DNS predictions give similar qualitative features for the tip flow, but the size and shape of the inlet separation bubble and shock positions differ noticeably. The RANS predictions are particularly insensitive to free-stream turbulence.

The Effect of Free-Stream Turbulence on Gas Turbine Blade Heat Transfer

1989 ◽  
Vol 111 (4) ◽  
pp. 497-501 ◽  
Author(s):  
V. Krishnamoorthy ◽  
S. P. Sukhatme
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbine ◽  
Free Stream ◽  
Flux Boundary Condition ◽  
Number Range ◽  
Free Stream Turbulence ◽  
Coefficient Distribution ◽  
The Heat Transfer Coefficient

This paper describes the results of systematic investigations undertaken to study the effect of free-stream turbulence on the heat transfer coefficient distribution around gas turbine rotor blades and nozzle guide vanes. The heat transfer coefficient distribution around the blade surface was obtained under a uniform heat flux boundary condition. Experiments were conducted in the Reynolds number range 2.0–8.1 × 105 (exit Mach number range 0.182 to 0.600) with the free-stream turbulence level in the range 1.0–21.3 percent. A new type of active turbulence generator was used for generating high turbulence levels. Correlations were obtained for the effect of free-stream turbulence on the local heat transfer coefficient in the laminar, transitional, and turbulent boundary layer regions.

Free-Stream Effects on the Cooling Performance of Cylindrical and Fan-Shaped Cooling Holes

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Christian Saumweber ◽  
Achmed Schulz
Keyword(s):  
Mach Number ◽  
Gas Flow ◽  
Free Stream ◽  
Pressure Ratio ◽  
Cross Flow ◽  
Wake Flow ◽  
Transfer Coefficients ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence ◽  
Hot Gas

From literature and our own studies, it is known that the effects of hot gas cross-flow and, in particular, the turbulence of the hot gas flow highly influence the spreading of the coolant in the near hole vicinity. Moreover, the velocity of the hot gas flow expressed by a hot gas Mach number obviously plays a much more important role in the case of diffuser holes than with simple cylindrical holes. To realize a certain blowing rate, a higher pressure ratio needs to be established in the case of higher Mach numbers. This in turn may strongly affect the diffusion process in the expanded portion of a fan-shaped cooling hole. The said effects will be discussed in great detail. The effects of free-stream Mach number and free-stream turbulence, including turbulence intensity, integral length scale, and periodic unsteady wake flow will be considered. The comparative study is performed by means of discharge coefficients and by local and laterally averaged adiabatic film cooling effectiveness and heat transfer coefficients. Both cooling holes have a length-to-diameter ratio of 6 and an inclination angle of 30 deg. The fan-shaped hole has an expansion angle of 14 deg. The effect of the coolant cross-flow at the hole entrance is not considered in this study, i.e., plenum conditions exist at the hole entrance.

Studies on Transitional Heat Transfer Characteristics Over Turbine Vane Surface Using a High Order LES Approach

2014 ◽  
Author(s):  
Debasish Biswas
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Gas Turbine ◽  
Free Stream ◽  
Suction Side ◽  
Boundary Layer Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
Turbine Vane ◽  
Turbine Airfoils

The boundary layer developing on a turbo-machinery blade usually starts as a laminar layer but in most situations it inevitably becomes turbulent. The transition from laminar to turbulent in the boundary layer, which often causes a significant change in operational performance of the machinery, is generally influenced by the free-stream turbulence level, the pressure gradient, and surface curvature, etc. Therefore, boundary layer transition is an important phenomenon experienced by the flow through gas turbine engines. A substantial fraction of the boundary layer on both sides of a gas turbine airfoil may be transitional. The extended transition zone exist due to strong favorable pressure gradients, found on both near the leading edge portion of the suction side and the pressure side, which serve to stabilize the boundary layer and consequently delay the transition process, even under high free-stream turbulence intensity (FSTI) in practical gas turbine. It is very important to properly model and predict the high FSTI transition mechanism, since boundary layer transition leads to substantial increase in friction coefficients and heat transfer rate. Boundary layer separation, which is expected to be a significant problem on the suction side of some high pressure turbine airfoils due to shock-boundary layer interaction, also depends strongly on the state of boundary layer with respect to transition. Acceleration rates, Reynolds numbers and FSTI play very important role in controlling the boundary layer transition on the pressure side of gas turbine airfoils. The main objective of the present work is to study the performance of a high order LES turbulence model in predicting the transitional heat transfer characteristics over turbine vane surface under high pressure turbine flow conditions. In this regard the model is assessed to the precise experimental data where measurements were carried out in moderate temperature using three-vane cascades under steady state conditions. Two types of vane configurations were used in the experiment. The aerodynamic configurations of the two vanes were carefully selected to emphasize fundamental differences in the character of suction surface pressure distributions and the consequent effect on surface heat transfer distributions. In both the experiments and the computations, principle independent parameters (Mach number, Reynolds number, turbulence intensity, and wall-to-gas temperature ratio) were varied over ranges consistent with actual engine operation. The computed results explained measured data very satisfactorily and helped to have a very good understanding of basic mechanism involved in the complex flow behavior and transition from laminar to turbulent flow.

An Experimental Convective Heat Transfer Investigation Around a Film-Cooled Gas Turbine Blade

1990 ◽  
Vol 112 (3) ◽  
pp. 497-503 ◽  
Author(s):  
C. Camci ◽  
T. Arts
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Gas Turbine ◽  
Convective Heat ◽  
Free Stream ◽  
Weight Ratio ◽  
Leading Edge ◽  
Suction Side ◽  
Turbine Rotor ◽  
Free Stream Turbulence

The present paper deals with an experimental convective heat transfer investigation around a film-cooled, high-pressure gas turbine rotor blade mounted in a stationary, linear cascade arrangement. The measurements were performed in the von Karman Institute Isentropic Light Piston Compression Tube facility. The test blade was made of Macor glass ceramic and was instrumented with thin film gages. The coolant flow was ejected simultaneously through the leading edge (three rows of holes), the suction side (two rows of holes), and the pressure side (one row of holes). The effects of overall mass weight ratio, coolant to free-stream temperature ratio, and free-stream turbulence were successively investigated.

High Free-Steam Turbulence Effects on Endwall Heat Transfer for a Gas Turbine Stator Vane

2000 ◽  
Vol 122 (4) ◽  
pp. 699-708 ◽  
Author(s):  
R. W. Radomsky ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Gas Turbine ◽  
Convective Heat ◽  
Free Stream ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Free Stream Turbulence ◽  
Stator Vane ◽  
The Mean

High free-stream turbulence along a gas turbine airfoil and strong secondary flows along the endwall have both been reported to increase convective heat transfer significantly. This study superimposes high free-stream turbulence on the naturally occurring secondary flow vortices to determine the effects on the flowfield and the endwall convective heat transfer. Measured flowfield and heat transfer data were compared between low free-stream turbulence levels (0.6 percent) and combustor simulated turbulence levels (19.5 percent) that were generated using an active grid. These experiments were conducted using a scaled-up, first-stage stator vane geometry. Infrared thermography was used to measure surface temperatures on a constant heat flux plate placed on the endwall surface. Laser-Doppler Velocimetry (LDV) measurements were performed of all three components of the mean and fluctuating velocities of the leading edge horseshoe vortex. The results indicate that the mean flowfields for the leading edge horseshoe vortex were similar between the low and high free-stream turbulence cases. High turbulence levels in the leading edge–endwall juncture were attributed to a vortex unsteadiness for both the low and high free-stream turbulence cases. While, in general, the high free-stream turbulence increased the endwall heat transfer, low augmentations were found to coincide with the regions having the most intense vortex motions. [S0889-504X(00)00704-2]

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