Characterization and Laboratory Simulation of Turbine Airfoil Surface Roughness and Associated Heat Transfer

1998 ◽  
Vol 120 (2) ◽  
pp. 337-342 ◽  
Author(s):  
D. G. Bogard ◽  
D. L. Schmidt ◽  
M. Tabbita
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Free Stream ◽  
Laboratory Simulation ◽  
Roughness Effects ◽  
Average Roughness ◽  
Airfoil Surface ◽  
Free Stream Turbulence

The physical characteristics of surface roughness observed on first-stage high-pressure turbine vanes that had been in service for a long period were investigated in this study. Profilometry measurements were utilized to provide details of the surface roughness formed by deposits of foreign materials on different parts of the turbine vane. Typical measures of surface roughness such as centerline average roughness values were shown to be inadequate for characterizing roughness effects. Using a roughness shape parameter originally derived from regular roughness arrays, the turbine airfoil roughness was characterized in terms of equivalent sand-grain roughness in order to develop an appropriate simulation of the surface for laboratory experiments. Two rough surface test plates were designed and fabricated. These test plates were evaluated experimentally to quantify the heat transfer rate for flow conditions similar to that which occurs on the turbine airfoil. Although the roughness levels on the two test plates were different by a factor of two, both surfaces caused similar 50 percent increases in heat transfer rates relative to a smooth surface. The effects of high free-stream turbulence, with turbulence levels from 10 to 17 percent, were also investigated. Combined free-stream turbulence and surface roughness effects were found to be additive, resulting in as much as a 100 percent increase in heat transfer rate.

scholarly journals Characterization and Laboratory Simulation of Turbine Airfoil Surface Roughness and Associated Heat Transfer

1996 ◽  
Author(s):  
David G. Bogard ◽  
Donald L. Schmidt ◽  
Martin Tabbita
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Free Stream ◽  
Laboratory Simulation ◽  
Roughness Effects ◽  
Average Roughness ◽  
Airfoil Surface ◽  
Free Stream Turbulence

The physical characteristics of surface roughness observed on 1st stage high pressure turbine vanes which had been in service for a long period were investigated in this study. Profilometry measurements were utilized to provide details of the surface roughness formed by deposits of foreign materials on different parts of the turbine vane. Typical measures of surface roughness such as centerline average roughness values were shown to be inadequate for characterizing roughness effects. Using a roughness shape parameter originally derived from regular roughness arrays, the turbine airfoil roughness was characterized in terms of equivalent sandgrain roughness in order to develop an appropriate simulation of the surface for laboratory experiments. Two rough surface test plates were designed and fabricated and these test plates were evaluated experimentally to quantify the heat transfer rate for flow conditions similar to that which occur on the turbine airfoil. Although the roughness levels on the two test plates were different by a factor of two, both surfaces caused similar 50% increases in heat transfer rates relative to a smooth surface. The effects of high free-stream turbulence, with turbulence levels from 10% to 17%, were also investigated. Combined free-stream turbulence and surface roughness effects were found to be additive, resulting in as much as a 100% increase in heat transfer rate.

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%.

Effects of Free-Stream Turbulence and Surface Roughness on Film Cooling

1996 ◽  
Author(s):  
Donald L. Schmidt ◽  
David G. Bogard
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Momentum Flux ◽  
Free Stream ◽  
Cooling Performance ◽  
Free Stream Turbulence ◽  
Adiabatic Effectiveness

A flat plate test section was used to study how high free-stream turbulence with large turbulence length scales, representative of the turbine environment, affect the film cooling adiabatic effectiveness and heat transfer coefficient for a round hole film cooling geometry. This study also examined cooling performance with combined high free-stream turbulence and a rough surface which simulated the roughness representative of an in-service turbine. The injection was from a single row of film cooling holes with injection angle of 30°. The density ratio of the injectant to the mainstream was 2.0 for the adiabatic effectiveness tests, and 1.0 for the heat transfer coefficient tests. Streamwise and lateral distributions of adiabatic effectiveness and heat transfer coefficients were obtained at locations from 2 to 90 hole diameters downstream. At small to moderate momentum flux ratios, which would normally be considered optimum blowing conditions, high free-stream turbulence dramatically decreased adiabatic effectiveness. However, at large momentum flux ratios, conditions for which the film cooling jet would normally be detached, high free-stream turbulence caused an increase in adiabatic effectiveness. The combination of high free-stream turbulence with surface roughness resulted in an increase in adiabatic effectiveness relative to the smooth wall with high free-stream turbulence. Heat transfer rates were relatively unaffected by a film cooling injection. The key result from this study was a substantial increase in the momentum flux ratios for maximum film cooling performance which occurred for high free-stream turbulence and surface roughness conditions which are more representative of actual turbine conditions.

Effect of Elevated Free-Stream Turbulence on Transitional Heat Transfer Over Dual-Scaled Rough Surfaces

2003 ◽  
Author(s):  
Ting Wang ◽  
Matthew C. Rice
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Surface Roughness ◽  
Vortex Shedding ◽  
Free Stream ◽  
Leading Edge ◽  
Test Surface ◽  
Dominant Effect ◽  
Free Stream Turbulence ◽  
Heat Transfer Phenomenon

The surface roughness over a serviced turbine airfoil is usually multi-scaled with varying features that are difficult to be universally characterized. However, it was previously discovered in low freestream turbulence conditions that the height of larger roughness produces separation and vortex shedding, which trigger early transition and exert a dominant effect on flow pattern and heat transfer. The geometry of the roughness and smaller roughness scales played secondary roles. This paper extends the previous study to elevated turbulence conditions with free-stream turbulence intensity ranging from 0.2–6.0 percent. A simplified test condition on a flat plate is conducted with two discrete regions having different surface roughness. The leading edge roughness is comprised of a sandpaper strip or a single cylinder. The downstream surface is either smooth or covered with sandpaper of grit sizes ranging from 100 ∼ 40 (Ra = 37 ∼ 119 μm). Hot wire measurements are conducted in the boundary layer to study the flow structure. The results of this study verify that the height of the largest-scale roughness triggers an earlier transition even under elevated turbulence conditions and exerts a more dominant effect on flow and heat transfer than does the geometry of the roughness. Heat transfer enhancements of about 30 ∼ 40 percent over the entire test surface are observed. The vortical motion, generated by the backward facing step at the joint of two roughness regions, is believed to significantly increase momentum transport across the boundary layer and bring the elevated turbulence from the freestream towards the wall. No such long-lasting heat transfer phenomenon is observed in low FSTI cases even though vortex shedding also exists in the low turbulence cases. The heat transfer enhancement decreases, instead of increases, as the downstream roughness height increases.

The Effect of Free-Stream Turbulence on Heat Transfer From a Rectangular Prism

1984 ◽  
Vol 106 (2) ◽  
pp. 268-275 ◽  
Author(s):  
D. C. McCormick ◽  
F. L. Test ◽  
R. C. Lessmann
Keyword(s):  
Heat Transfer ◽  
Pressure Gradient ◽  
Transfer Rate ◽  
Free Stream ◽  
Two Dimensional ◽  
Free Stream Turbulence ◽  
Favorable Pressure Gradient ◽  
Temperature Heat ◽  
Predicted Values ◽  
Rectangular Body

This paper discussses the effect of free-stream turbulence on the constant temperature heat transfer rate from the surface of a two-dimensional rectangular body that is subject to a strongly favorable pressure gradient. Free-stream turbulence levels of 2 to 5 percent enhanced the heat transfer by 48 to 55 percent over predicted laminar values. Free-stream turbulence levels of 10 to 35 percent produced heat transfer results that behaved in some aspects as turbulent predictions, although considerably enhanced in magnitude over the predicted values.

scholarly journals Experimental Study of the Iso-Heat-Transfer-Rate Lines on the End-Wall of a Turbine Cascade

1979 ◽  
Author(s):  
D. P. Georgiou ◽  
M. Godard ◽  
B. E. Richards
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Fast Response ◽  
Intensity Level ◽  
Turbine Cascade ◽  
Isentropic Compression ◽  
Free Stream Turbulence ◽  
Good Spatial Resolution ◽  
End Wall

Experiments were conducted to study the distribution of the iso-heat-transfer-rate lines on the end-wall of a turbine cascade. A light piston isentropic compression tube facility was used for the experiments together with thin film heat transfer gages and a fast response analog recording system. The conditions fully represented typical Mach and Reynolds numbers, temperature ratio as well as the blade section of a modern cooled turbine. Special attention was paid to the need for good spatial resolution. The study includes the effect of the free-stream turbulence intensity level and the inlet boundary layer thickness. A subsonic compressible flow calculation method was used to predict the potential flow streamlines and a visualization method was used to study the limiting streamlines on the end wall. Furthermore, the distribution of various heat transfer parameters (e.g., qω, St) along these streamlines have undergone detailed study and some uniformity is shown to exist.

Comparison of Additively Manufactured Louvered Plate-Fin Heat Exchangers

2019 ◽  
Vol 12 (1) ◽  
Author(s):  
Michael Bichnevicius ◽  
David Saltzman ◽  
Stephen Lynch
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Pressure Drop ◽  
Heat Transfer Rate ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Print Quality ◽  
Side Pressure ◽  
Oil Cooler ◽  
Fin Thickness

Abstract Additive manufacturing (AM) enables improved heat exchanger (HX) designs where performance is based on the achievable geometry. However, consequences of the AM process that affect HX performance such as increased surface roughness, dimensional tolerance issues, and defects like cracks may vary among identically designed AM parts due to AM machine settings. This paper experimentally compares the thermal and hydraulic performance of three AM HXs built using a traditionally manufactured, stamped aluminum oil cooler design. The AM HXs exhibited significantly higher air-side pressure drop and higher heat transfer rate than the traditional HX in large part due to increased AM surface roughness. Among AM HXs, one AM HX had notably higher heat transfer rate and air-side pressure drop due to poor print quality on the thin air-side fin features. The fin thickness among AM HXs also varied by about 15%, and there were only slight differences in surface roughness. This study indicates that functional HXs built using AM vary in performance even when the same digital model is used to print them and that AM HXs as a group can perform considerably differently than their traditional counterparts.

Wall Roughness Effect on Heat Transfer Rate of the Turbulent Gas-Solid Flow in Inclined Pipes

2014 ◽  
Author(s):  
Adel Ebadi ◽  
Zohreh Mansoori ◽  
Majid Saffar-Avval ◽  
Goodarz Ahmadi
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Nusselt Number ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Wall Region ◽  
Fluid Temperature ◽  
Wall Roughness ◽  
Mean Flow ◽  
Inclined Pipes

The effects of wall surface roughness on the rate of heat transfer and temperature profiles in turbulent gas-solid flows in pipes at different inclination angles were studied. The earlier developed computational model for 3D flows including the four-way interactions was extended and used in this study for evaluating the mean flow, turbulence intensity and thermal fields. Interaction of particles with the rough wall was included by introducing the available stochastic wall roughness models (shadow effect model) for the dispersed phase in the computational program. It was found that changes in the particle dispersion and particle concentration altered the Nusselt number and heat transfer rate in different regions of the pipe. The Nusselt number decreased in the lower part of the duct for horizontal and inclined pipes due to the reduction in the settling velocity. The surface roughness also altered the heat transfer coefficient in the periphery of the vertical riser. The simulation results showed that the fluid temperature was reduced in the pipe core and increased near the wall region for inclined pipes. On the other hand, particle temperature increased and flattened in the entire pipe cross section.

Unsteady Interaction Effects on a Transitional Turbine Blade Boundary Layer

1989 ◽  
Vol 111 (2) ◽  
pp. 162-168 ◽  
Author(s):  
D. A. Ashworth ◽  
J. E. LaGraff ◽  
D. L. Schultz
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Guide Vane ◽  
Turbine Rotor ◽  
Surface Boundary ◽  
Suction Surface ◽  
Wide Bandwidth ◽  
Free Stream Turbulence

Results are presented illustrating the detailed behavior of the suction surface boundary layer of a transonic gas turbine rotor in a two-dimensional cascade under the influence of both free-stream turbulence and simulated nozzle guide vane wakes and shocks. The instrumentation included thin film resistance thermometers along with electrical analogues of the one-dimensional heat conduction equations to obtain wide bandwidth heat transfer rate measurements in a short duration wind tunnel. This instrumentation provides sufficient time resolution to track individual wake and shock-related events and also the turbulent bursts of a transitional boundary layer. Wide bandwidth surface pressure transducers and spark Schlieren photography were used in support of these heat transfer measurements. The results showed a direct relationship between the passage of wake disturbances and transient surface heat transfer enhancements. It was possible to track both wake and transitional events along the surface and to compare these with the expected convection rates. Analysis of the signals allowed direct calculations of intermittency factors, which compared well with predictions. Additional effects due to a moving shock/boundary layer interaction were investigated. These resulted in marked variations in heat transfer rate both above and below the laminar values. These excursions were associated with separation and re-attachment phenomena.

Sign in / Sign up

Export Citation Format

Share Document