Simultaneous Heat Flux and Velocity Measurements in a Transonic Turbine Cascade

2004 ◽  
Vol 127 (3) ◽  
pp. 502-506 ◽  
Author(s):  
D. G. Holmberg ◽  
T. E. Diller
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Free Stream ◽  
Turbine Blades ◽  
Frequency Domain Analysis ◽  
Turbine Cascade ◽  
Velocity Measurements ◽  
Time Resolved ◽  
Free Stream Turbulence ◽  
High Frequency Response

The gas turbine engine combustor generates turbulence that increases heat transfer on downstream turbine blades, but the mechanisms of that heat transfer are not fully understood. In this work, simultaneous time-resolved surface heat flux and velocity measurements have been made at three locations on the pressure surface of a high-turning transonic airfoil. Grids were used upstream of the linear turbine cascade to produce free-stream turbulence with two different inlet length scales, but the same turbulence intensity. High-frequency response instrumentation was used to obtain both steady and unsteady measurements. Results show that the time-averaged heat transfer is larger for the flow with the smaller integral length scale. Frequency-domain analysis demonstrates coherence between the fluctuations of heat flux and velocity over a broad range of frequencies. This is a direct indication that free-stream turbulent eddies penetrate completely through the boundary layer to the surface.

Experimental Performance of a Heat Flux Microsensor

1991 ◽  
Vol 113 (2) ◽  
pp. 246-250 ◽  
Author(s):  
J. M. Hager ◽  
S. Simmons ◽  
D. Smith ◽  
S. Onishi ◽  
L. W. Langley ◽  
...  
Keyword(s):  
Heat Flux ◽  
Convection Heat Transfer ◽  
Active Surface ◽  
High Heat ◽  
Active Surface Area ◽  
High Heat Flux ◽  
Time Resolved ◽  
Free Stream Turbulence ◽  
High Frequency Response ◽  
Measurement Surface

The performance characteristics of a heat flux microsensor have been measured and analyzed. This is a new heat flux gage system that is made using microfabrication techniques. The gages are small, have high frequency response, can measure very high heat flux, and output a voltage directly proportional to the heat flux. Each gage consists of a thin thermal resistance layer sandwiched between many thermocouple pairs forming a differential thermopile. Because the gage is made directly on the measurement surface and the total thickness is less than 2 μm, the presence of the gage contributes negligible flow and thermal disruption. The active surface area of the gage is 3 mm by 4 mm, with the leads attached outside this area to relay the surface heat flux and temperature signals. Gages were made and tested on glass and silicon substrates. The steady and unsteady response was measured experimentally and compared with analytical predictions. The analysis was performed using a one-dimensional, transient, finite-difference model of the six layers comprising the gage plus the substrate. Steady-state calibrations were done on a convection heat transfer apparatus and the transient response was measured to step changes of the imposed radiative flux. As an example of the potential capabilities, the time-resolved heat flux was measured at a stagnation point with imposed free-stream turbulence. A hot-film probe placed outside the boundary layer was used to provide a simultaneous signal showing the corresponding turbulent velocity fluctuations.

Numerical Approach at Flat Plate for Predicting the Film Cooling Effectiveness Part A: Effect Blowing Ratio

2018 ◽  
Vol 16 ◽  
pp. 30-44 ◽  
Author(s):  
Farouk Kebir ◽  
Azzeddine Khorsi
Keyword(s):  
Heat Transfer ◽  
Flat Plate ◽  
Film Cooling ◽  
Thermal Stresses ◽  
Free Stream ◽  
Turbine Blades ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Free Stream Turbulence ◽  
Blowing Ratio

Film cooling is vital for gas turbine blades to protect them from thermal stresses and high temperatures due to the hot gas flow in the blade surface. Film cooling is applied to almost all external surfaces associated with aerodynamic profiles that are exposed to hot combustion gases such as main bodies, end-walls, blade tips and leading edges. In a review of the literature, it was found that there are strong effects of free-stream turbulence, surface curvature and hole shape on film cooling performance also blowing ratio. The performance of the film cooling is difficult to predict due to the inherent complex flow fields along the surfaces of the airfoil components in the turbine engines. From all what we introducing the film cooling is reviewed through a discussion of the analyses methodologies, a physical description, and the various influences on film-cooling performance. Initially Computational analysis was done on a flat plate with hole inclined at 55° to the surface plate. This study focuses on the efficient computation of film cooling flows with three blowing ratio. The numerical results show the effectiveness cooling and heat transfer behavior with increasing injection blowing ratio M (0.5, 1, and 1.5). The influence of increased blade film cooling can be assessed via the values of Nusselt number in terms of reduced heat transfer to the blade. Predictions of film effectiveness are compared with experimental results for a circular jet at blowing ratios ranging from 0.5, 1.0 and 1.5. The present results are obtained at a free stream turbulence of 10%, which are the typical conditions upstream of the effectiveness is generally lower for a large stream-wise angle of 55°.

Simulation of Heat Transfer From Flow With High Free-Stream Turbulence to Turbine Blades

1997 ◽  
Vol 119 (2) ◽  
pp. 284-291 ◽  
Author(s):  
E. Fridman
Keyword(s):  
Heat Transfer ◽  
Free Stream ◽  
Turbine Blades ◽  
Plate Boundary ◽  
Transfer Coefficients ◽  
Relaxation Length ◽  
Free Stream Turbulence ◽  
Heat Transfer Coefficients ◽  
High Level ◽  
Flat Plate Boundary Layer

The present investigation is devoted to one of the most difficult problems in the gas turbine industry: predicting the heat transfer to turbine blades. It is known that one of the important factors that affects heat transfer coefficients is a significant level of turbulence in the flow that surrounds a turbine blade. The influence of free-stream turbulence on heat transfer coefficients for a flat plate boundary layer with zero pressure gradient or in the vicinity of the stagnation point of a circular cylinder is investigated numerically. An algebraic relaxation-length model of turbulence is applied in order to simulate real situations in flows with a high level of free-stream turbulence. The results, temperature and velocity profiles, and heat transfer and drag coefficients, are compared with available experimental data. The proposed method is recommended for practical calculations of heat transfer coefficients on turbine blades.

Free-Stream Turbulence Effects on Local Heat Transfer from a Sphere

1972 ◽  
Vol 94 (1) ◽  
pp. 7-14 ◽  
Author(s):  
L. B. Newman ◽  
E. M. Sparrow ◽  
E. R. G. Eckert
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Free Stream ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Flux Sensor ◽  
Forward Region ◽  
Number Range ◽  
Free Stream Turbulence

Experiments involving both heat-transfer and turbulence-field measurements were performed to determine the influence of free-stream turbulence on the local heat transfer from a sphere situated in a forced-convection airflow. The research was facilitated by a miniature heat-flux sensor which could be positioned at any circumferential location on the equator of the sphere. Turbulence grids were employed to generate free-stream turbulence with intensities of up to 9.4 percent. The Reynolds-number range of the experiments was from 20,000 to 62,000. The results indicate that the local heat flux in the forward region of the sphere is uninfluenced by free-stream turbulence levels of up to about 5 percent. For higher turbulence levels, the heat-flux increases with the turbulence intensity, the greatest heat-flux augmentation found here being about 15 percent. Furthermore, at the higher turbulence intensities, there appears to be a departure from the half-power Reynolds-number dependence of the stagnation-point Nusselt number. Turbulent separation occurred at Reynolds numbers of 42,000 and 62,000 for a turbulence level of 9.4 percent, these values being well below the transition Reynolds number of 2 × 105 for a sphere situated in a low-turbulence flow.

The Unsteady Effect of Passing Shocks on Pressure Surface Versus Suction Surface Heat Transfer in Film-Cooled Transonic Turbine Blades

2003 ◽  
Author(s):  
A. C. Smith ◽  
A. C. Nix ◽  
T. E. Diller ◽  
W. F. Ng
Keyword(s):  
Heat Transfer ◽  
Shock Wave ◽  
Heat Flux ◽  
Film Cooling ◽  
Turbine Blades ◽  
Surface Heat ◽  
Suction Surface ◽  
Time Resolved ◽  
Pressure Surface ◽  
Transonic Turbine

This paper documents the measurement of the unsteady effects of passing shock waves on film cooling heat transfer on both the pressure and suction surfaces of first stage transonic turbine blades with leading edge showerhead film cooling. Experiments were performed for several cooling blowing ratios with an emphasis on time-resolved pressure and heat flux measurements on the pressure surface. Results without film cooling on the pressure surface demonstrated that increases in heat flux were a result of shock heating (the increase in temperature across the shock wave) rather than shock interaction with the boundary layer or film layer. Time-resolved measurements with film cooling demonstrated that the relatively strong shock wave along the suction surface appears to retard coolant ejection there and causes excess coolant to be ejected from pressure surface holes. This actually causes a decrease in heat transfer on the pressure surface during a large portion of the shock passing event. The magnitude of the decrease is almost as large as the increase in heat transfer without film cooling. The decrease in coolant ejection from the suction surface holes did not appear to have any effects on suction surface heat transfer.

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.

Time-Resolved Heat Transfer Measurements on the Tip Wall of a Ribbed Channel Using a Novel Heat Flux Sensor: Part I — Sensor and Benchmarks

2006 ◽  
Author(s):  
Tim Roediger ◽  
Helmut Knauss ◽  
Uwe Gaisbauer ◽  
Ewald Kraemer ◽  
Sean Jenkins ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbine Blades ◽  
Temperature Fields ◽  
Heat Flux Sensor ◽  
Internal Cooling ◽  
Time Resolved ◽  
Flux Measurements ◽  
Working Principle ◽  
Flux Sensor

A novel heat flux sensor was tested which allows for time-resolved heat flux measurements in internal ribbed channels related to the study of passages in gas turbine blades. The working principle of the Atomic Layer Thermopile (ALTP) sensor is based on a thermoelectric field created by a temperature gradient over an YBCO crystal (the transverse Seebeck effect). The sensors very fast frequency response allows for highly time-resolved heat flux measurements up to the 1 MHz range. This paper explains the design and working principle of the sensor, as well as the benchmarking of the sensor for several flow conditions. For internal cooling passages, this novel sensor allows for highly accurate, time-resolved measurements of heat transfer coefficients, leading to a greater understanding of the influence of fluctuations in temperature fields.

Time-Resolved Heat Transfer Measurements on the Tip Wall of a Ribbed Channel Using a Novel Heat Flux Sensor—Part I: Sensor and Benchmarks

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Tim Roediger ◽  
Helmut Knauss ◽  
Uwe Gaisbauer ◽  
Ewald Kraemer ◽  
Sean Jenkins ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbine Blades ◽  
Temperature Fields ◽  
Heat Flux Sensor ◽  
Internal Cooling ◽  
Time Resolved ◽  
Flux Measurements ◽  
Working Principle ◽  
Flux Sensor

A novel heat flux sensor was tested that allows for time-resolved heat flux measurements in internal ribbed channels related to the study of passages in gas turbine blades. The working principle of the atomic layer thermopile (ALTP) sensor is based on a thermoelectric field created by a temperature gradient over an yttrium-barium-copper-oxide (YBCO) crystal (the transverse Seebeck effect). The sensors very fast frequency response allows for highly time-resolved heat flux measurements up to the 1MHz range. This paper explains the design and working principle of the sensor, as well as the benchmarking of the sensor for several flow conditions. For internal cooling passages, this novel sensor allows for highly accurate, time-resolved measurements of heat transfer coefficients, leading to a greater understanding of the influence of fluctuations in temperature fields.

The Effects of Free-Stream Turbulence Intensity and Velocity Distribution on Heat Transfer to Curved Surfaces

1978 ◽  
Vol 100 (1) ◽  
pp. 159-168 ◽  
Author(s):  
A. Brown ◽  
R. C. Burton
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Turbine Blades ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Boundary Layer Transition ◽  
Stream Velocity ◽  
Layer Transition ◽  
Free Stream Turbulence

This paper describes a novel method for measuring the local heat-transfer distribution over a curved surface. The effect of free-stream turbulence intensity, ranging in value from 0.016 to 0.092, on local heat transfer is investigated for a range of Reynolds numbers from 2.0 × 105 to 7.7 × 105. The geometry of the rig was modified to consider three free-stream velocity distributions covering distributions currently in use on suction surfaces of turbine blades. The results are compared with other workers’ experimental results and with available prediction techniques for heat transfer in laminar and turbulent boundary layers. Special attention is paid to the region of boundary-layer transition.

scholarly journals Effects of Surface Riblets and Free-Stream Turbulence on Heat Transfer in a Linear Turbine Cascade

1994 ◽  
Author(s):  
Paul K. Maciejewski ◽  
Richard B. Rivir
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Test ◽  
Transfer Rate ◽  
Free Stream ◽  
Test Surface ◽  
Test Results ◽  
Turbine Cascade ◽  
Average Heat ◽  
Free Stream Turbulence

The present study is an experimental investigation of the effects of free-stream turbulence and surface riblets on the heat transfer rate in a linear turbine cascade. The primary goal of the study is to determine if surface riblets will reduce the average heat transfer rate in a cascade in the absence and in the presence of free-stream turbulence. A smooth, airfoil shaped, constant temperature, heat transfer test surface was inserted into a linear cascade facility where heat transfer tests were run at three levels of Reynolds number and two levels of free-stream turbulence. The heat transfer test surface was then removed from the facility so that riblets could be engraved on its surface. The newly ribleted heat transfer surface was then re-inserted into the cascade facility, where a second set of heat transfer tests were run at the same set of conditions used during the testing of the test surface while it was smooth. The test results indicate that, under certain conditions, surface riblets reduce the average heat transfer rate in the cascade by 7%.

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