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%.

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 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.

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.

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 Heat Transfer Behaviour Inside a Sinusoidal Cavity Using Water Based Tio2 Nanofluid

2018 ◽  
Vol 37 ◽  
pp. 121-129 ◽  
Author(s):  
Goutam Saha
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Average Heat ◽  
Water Based ◽  
Vertical Walls ◽  
Left And Right ◽  
Lower Temperature

A numerical investigation is carried out to observe the augmentation of heat transfer because of the presence of TiO2 nanofluid inside a sinusoidal cavity. In this study, upper and lower walls of the cavity are considered adiabatic, higher and lower temperature are maintained at left and right vertical walls respectively. Also, 2D contour of velocity and temperature with average heat transfer rate are presented and discussed. Our findings show that augmentation of heat transfer is feasible with the increase of concentrations of nanoparticles.GANIT J. Bangladesh Math. Soc.Vol. 37 (2017) 121-129

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.

Experimental and Numerical Studies of Natural Convection With Flow Separation in Upward-Facing Inclined Open Cavities

1993 ◽  
Vol 115 (3) ◽  
pp. 592-605 ◽  
Author(s):  
R. A. Showole ◽  
J. D. Tarasuk
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Rate ◽  
Flow Separation ◽  
Transfer Rate ◽  
Numerical Results ◽  
Average Heat ◽  
Aspect Ratios ◽  
Open Cavities ◽  
Flow Reattachment

Steady two-dimensional laminar natural convection heat transfer from isothermal horizontal and inclined open cavities of rectangular cross section has been investigated experimentally using a Mach-Zehnder interferometer and numerically by a finite difference technique. Experimental results are presented for Prandtl number, Pr = 0.7, Rayleigh numbers from 104 to 5 × 105, cavity aspect ratios, A (or h/w) = 0.25, 0.5, and 1.0, and inclination angles (or angles of rotation about the longitudinal axis), θ = 0, 30, 45, and 60 deg to the horizontal. The numerical model uses a relaxation technique to solve the governing elliptic, partial differential equations. Numerical results are presented for the range of Rayleigh number, 103 ≤ Raw ≤ 5 × 105, θ = 0 and 45 deg, and A = 1. Flow and temperature patterns, velocity and temperature profiles, and local and average heat transfer rates are presented. Flow recirculation with two counterrotating convective rolls developed in the cavity at Ra ≥ 105. The inclination of the cavity induced flow entrainment, causing flow separation at the lower corner and flow reattachment at the upper corner of the aperture opening except in shallow cavities, A < 0.5, where the flow reattachment occurred on the base of the inclined cavity. For all Ra numbers, the first inclination of the cavity from the horizontal caused a significant increase in the average heat transfer rate, but a further increase in the inclination angle caused very small increase in heat transfer rate. However, for every angle of inclination considered, the average heat transfer rate increased significantly as Ra was increased. The equation of the form Nu = mRan, where 0.018 ≤ m ≤ 0.088 and 0.325 ≤ n ≤ 0.484, correlates the experimental and numerical results satisfactorily for the range of Ra, 104 ≤ Ra ≤ 5 × 105 and of θ, 0 ≤ θ ≤ 60 deg. The present experimental and numerical results are in good agreement with the results reported in the literature.

scholarly journals Thermal Characteristics of Slinky-Coil Ground Heat Exchanger with Discrete Double Inclined Ribs

Resources ◽  
2020 ◽  
Vol 9 (9) ◽  
pp. 105
Author(s):  
Teguh Hady Ariwibowo ◽  
Akio Miyara
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Heat Transfer Rate ◽  
Thermal Performance ◽  
Transfer Rate ◽  
Ground Heat Exchanger ◽  
Average Heat ◽  
Thermal Mixing

The slinky ground heat exchanger (GHE) is the most widely utilized horizontal-type GHE, however, this GHE has a low curvature coil. The GHE has poor thermal mixing, especially at a low flowrate. At this flowrate, the coil heat exchanger has similar performance to a straight tube heat exchanger. Discrete double-inclined ribs (DDIR) are well known for their good thermal mixing by generating a vortex in straight tubes. In this paper, a numerical analysis of thermal performance for the plain coil and DDIR coil is discussed. It was found that the thermal performance of the DDIR coil was slightly higher than that of the plain coil in laminar flow. In turbulent flow, the DDIR coil was superior to the plain coil only in the first 149-min operation. The first 60-min analysis shows that in laminar flow, the average heat transfer rate in the plain coil is 59 W/m and in the DDIR coil is 60.1 W/m. In turbulent flow, the average heat transfer rate is 62 W/m, and the plain coil is 62.3 W/m. The copper DDIR coil material produced a better heat transfer rate than that of the composite and High-Density Polyethylene (HDPE). Sandy clay has the highest heat transfer rate. The influence of ground thermal conductivity on the performance of the GHE is more dominant than convection in the DDIR coil.

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