scholarly journals Effects of High Freestream Turbulence Levels and Length Scales on Stator Vane Heat Transfer

1998 ◽  
Author(s):  
R. W. Radomsky ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Reynolds Numbers ◽  
Surface Heat ◽  
Laser Doppler Velocimeter ◽  
Freestream Turbulence ◽  
Length Scales ◽  
Surface Heat Transfer ◽  
Stator Vane

Gaining a good understanding of how high freestream turbulence augments heat transfer is important for predicting thermal loadings for turbine blades and vanes. This study was aimed at documenting the surface heat transfer and the highly turbulent flowfield around a stator vane. The effects of turbulence levels between 11% and 24% were studied. At the highest turbulence level, two different Reynolds numbers (Reex = 6 × 105 and 1.2 × 106) and two different length scales were also studied. Three-component laser Doppler velocimeter measurements of the velocity fluctuations indicated that downstream of the active grid there was an initial decay of the turbulent kinetic energy which then leveled off at about one leading edge radius upstream of the vane. Inside the vane passage the turbulent kinetic energy increased slightly and then decayed through the passage. The surface heat transfer showed the largest augmentations on the pressure side of the vane with higher augmentations at higher turbulence levels, smaller length scales, and higher Reynolds numbers.

Flowfield Measurements for a Highly Turbulent Flow in a Stator Vane Passage

1999 ◽  
Author(s):  
R. W. Radomsky ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Reynolds Shear Stress ◽  
Correlation Coefficients ◽  
Leading Edge ◽  
Surface Heat ◽  
Laser Doppler Velocimeter ◽  
Surface Heat Transfer ◽  
Turbine Vanes ◽  
Stator Vane

Turbine vanes experience high convective surface heat transfer as a consequence of the turbulent flow exiting the combustor. Before improvements to vane heat transfer predictions through boundary layer calculations can be made, we need to understand how the turbulent flow in the inviscid region of the passage reacts as it passes between two adjacent turbine vanes. In this study, a scaled-up turbine vane geometry was used in a low-speed wind tunnel simulation. The test section included a central airfoil with two adjacent vanes. To generate the 20% turbulence levels at the entrance to the cascade, which simulates levels exiting the combustor, an active grid was used. Three-component laser Doppler velocimeter measurements of the mean and fluctuating quantities were measured in a plane at the vane mid-span. Coincident velocity measurements were made to quantify Reynolds shear stress and correlation coefficients. The energy spectra and length scales were also measured to give a complete set of inlet boundary conditions that can be used for numerical simulations. The results show that the turbulent kinetic energy throughout the inviscid region remained relatively high. The surface heat transfer measurements indicated high augmentation near the leading edge as well as the pressure side of the vane as a result of the elevated turbulence levels.

Flowfield Measurements for a Highly Turbulent Flow in a Stator Vane Passage

1999 ◽  
Vol 122 (2) ◽  
pp. 255-262 ◽  
Author(s):  
R. W. Radomsky ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Reynolds Shear Stress ◽  
Correlation Coefficients ◽  
Leading Edge ◽  
Surface Heat ◽  
Laser Doppler Velocimeter ◽  
Surface Heat Transfer ◽  
Turbine Vanes ◽  
Stator Vane

Turbine vanes experience high convective surface heat transfer as a consequence of the turbulent flow exiting the combustor. Before improvements to vane heat transfer predictions through boundary layer calculations can be made, we need to understand how the turbulent flow in the inviscid region of the passage reacts as it passes between two adjacent turbine vanes. In this study, a scaled-up turbine vane geometry was used in a low-speed wind tunnel simulation. The test section included a central airfoil with two adjacent vanes. To generate the 20 percent turbulence levels at the entrance to the cascade, which simulates levels exiting the combustor, an active grid was used. Three-component laser-Doppler velocimeter measurements of the mean and fluctuating quantities were measured in a plane at the vane midspan. Coincident velocity measurements were made to quantify Reynolds shear stress and correlation coefficients. The energy spectra and length scales were also measured to give a complete set of inlet boundary conditions that can be used for numerical simulations. The results show that the turbulent kinetic energy throughout the inviscid region remained relatively high. The surface heat transfer measurements indicated high augmentation near the leading edge as well as the pressure side of the vane as a result of the elevated turbulence levels. [S0889-504X(00)02302-3]

The Effects of Freestream Turbulence, Turbulence Length Scale, and Exit Reynolds Number on Turbine Blade Heat Transfer in a Transonic Cascade

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
J. S. Carullo ◽  
S. Nasir ◽  
R. D. Cress ◽  
W. F. Ng ◽  
K. A. Thole ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Surface Heat ◽  
Length Scale ◽  
Freestream Turbulence ◽  
Surface Heat Transfer ◽  
Mach Numbers ◽  
Turbulence Length ◽  
Turbulence Length Scale

This paper experimentally investigates the effect of high freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the surface heat transfer distribution of a turbine blade at realistic engine Mach numbers. Passive turbulence grids were used to generate freestream turbulence levels of 2%, 12%, and 14% at the cascade inlet. The turbulence grids produced length scales normalized by the blade pitches of 0.02, 0.26, and 0.41, respectively. Surface heat transfer measurements were made at the midspan of the blade using thin film gauges. Experiments were performed at the exit Mach numbers of 0.55, 0.78, and 1.03, which represent flow conditions below, near, and above nominal conditions. The exit Mach numbers tested correspond to exit Reynolds numbers of 6×105, 8×105, and 11×105, based on true chord. The experimental results showed that the high freestream turbulence augmented the heat transfer on both the pressure and suction sides of the blade as compared with the low freestream turbulence case. At nominal conditions, exit Mach 0.78, average heat transfer augmentations of 23% and 35% were observed on the pressure side and suction side of the blade, respectively.

The Effects of Freestream Turbulence, Turbulence Length Scale and Exit Reynolds Number on Turbine Blade Heat Transfer in a Transonic Cascade

2007 ◽  
Author(s):  
J. S. Carullo ◽  
S. Nasir ◽  
R. D. Cress ◽  
W. F. Ng ◽  
K. A. Thole ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Surface Heat ◽  
Length Scale ◽  
Freestream Turbulence ◽  
Surface Heat Transfer ◽  
Mach Numbers ◽  
Turbulence Length ◽  
Turbulence Length Scale

This paper experimentally investigates the effect of high freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the surface heat transfer distribution of a turbine blade at realistic engine Mach numbers. Passive turbulence grids were used to generate freestream turbulence levels of 2%, 12%, and 14% at the cascade inlet. The turbulence grids produced length scales normalized by the blade pitch of 0.02, 0.26, and 0.41, respectively. Surface heat transfer measurements were made at the midspan of the blade using thin film gauges. Experiments were performed at exit Mach numbers of 0.55, 0.78 and 1.03 which represent flow conditions below, near, and above nominal conditions. The exit Mach numbers tested correspond to exit Reynolds numbers of 6 × 105, 8 × 105, and 11 × 105, based on true chord. The experimental results showed that the high freestream turbulence augmented the heat transfer on both the pressure and suction sides of the blade as compared to the low freestream turbulence case. At nominal conditions, exit Mach 0.78, average heat transfer augmentations of 23% and 35% were observed on the pressure side and suction side of the blade, respectively.

scholarly journals Heat Transfer Enhancement for Finned-Tube Heat Exchangers With Winglets

2000 ◽  
Author(s):  
James E. O’Brien ◽  
Manohar S. Sohal
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Circular Tube ◽  
Reynolds Numbers ◽  
Surface Heat ◽  
Operating Conditions ◽  
Transfer Enhancement ◽  
Height Ratio ◽  
Surface Heat Transfer ◽  
Delta Winglet

Abstract This paper presents the results of an experimental study of forced convection heat transfer in a narrow rectangular duct fitted with a circular tube and/or a delta-winglet pair. The duct was designed to simulate a single passage in a fin-tube heat exchanger. Heat transfer measurements were obtained using a transient technique in which a heated airflow is suddenly introduced to the test section. High-resolution local fin-surface temperature distributions were obtained at several times after initiation of the transient using an imaging infrared camera. Corresponding local fin-surface heat transfer coefficient distributions were then calculated from a locally applied one-dimensional semi-infinite inverse heat conduction model. Heat transfer results were obtained over an airflow rate ranging from 1.51 × 10−3 to 14.0 × 10−3 kg/s. These flow rates correspond to a duct-height Reynolds number range of 670–6300 with a duct height of 1.106 cm and a duct width-to-height ratio, W/H, of 11.25. The test cylinder was sized such that the diameter-to-duct height ratio, D/H is 5. Results presented in this paper reveal visual and quantitative details of local fin-surface heat transfer distributions in the vicinity of a circular tube, a delta-winglet pair, and a combination of a circular tube and a delta-winglet pair. Comparisons of local and average heat transfer distributions for the circular tube with and without winglets are provided. Overall mean fin-surface Nusselt-number results indicate a significant level of heat transfer enhancement associated with the deployment of the winglets with the circular cylinder. At the lowest Reynolds numbers (which correspond to the laminar operating conditions of existing geothermal aircooled condensers), the enhancement level is nearly a factor of two. At higher Reynolds numbers, the enhancement level is close to 50%.

Experimental Measurements and Modeling of the Effects of Large-Scale Freestream Turbulence on Heat Transfer

2004 ◽  
Author(s):  
A. C. Nix ◽  
T. E. Diller ◽  
W. F. Ng
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbine Blade ◽  
Large Scale ◽  
Surface Heat ◽  
Integral Length Scale ◽  
Length Scale ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Surface Heat Transfer

The influence of freestream turbulence representative of the flow downstream of a modern gas turbine combustor and first stage vane on turbine blade heat transfer has been measured and analytically modeled in a linear, transonic turbine cascade. High intensity, large length-scale freestream turbulence was generated using a passive turbulence-generating grid to simulate the turbulence generated in modern combustors after passing through the first stage vane row. The grid produced freestream turbulence with intensity of approximately 10–12% and an integral length scale of 2 cm (Λx/c = 0.15) near the entrance of the cascade passages. Mean heat transfer results with high turbulence showed an increase in heat transfer coefficient over the baseline low turbulence case of approximately 8% on the suction surface of the blade, with increases on the pressure surface of approximately 17%. Time-resolved surface heat transfer and passage velocity measurements demonstrate strong coherence in velocity and heat flux at a frequency correlating with the most energetic eddies in the turbulence flow field (the integral length-scale). An analytical model was developed to predict increases in surface heat transfer due to freestream turbulence based on local measurements of turbulent velocity fluctuations and length-scale. The model was shown to predict measured increases in heat flux on both blade surfaces in the current data. The model also successfully predicted the increases in heat transfer measured in other work in the literature, encompassing different geometries (flat plate, cylinder, turbine vane and turbine blade) and boundary layer conditions.

scholarly journals Heat Transfer Enhancement for Finned-Tube Heat Exchangers With Winglets

2005 ◽  
Vol 127 (2) ◽  
pp. 171-178 ◽  
Author(s):  
James E. O’Brien ◽  
Manohar S. Sohal
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Circular Tube ◽  
Reynolds Numbers ◽  
Surface Heat ◽  
Operating Conditions ◽  
Transfer Enhancement ◽  
Height Ratio ◽  
Surface Heat Transfer ◽  
Delta Winglet

This paper presents the results of an experimental study of forced convection heat transfer in a narrow rectangular duct fitted with a circular tube and/or a delta-winglet pair. The duct was designed to simulate a single passage in a fin-tube heat exchanger. Heat transfer measurements were obtained using a transient technique in which a heated airflow is suddenly introduced to the test section. High-resolution local fin-surface temperature distributions were obtained at several times after initiation of the transient using an imaging infrared camera. Corresponding local fin-surface heat transfer coefficient distributions were then calculated from a locally applied one-dimensional semi-infinite inverse heat conduction model. Heat transfer results were obtained over an airflow rate ranging from 1.51×10−3 to 14.0×10−3kg/s. These flow rates correspond to a duct-height Reynolds number range of 670–6300 with a duct height of 1.106 cm and a duct width-to-height ratio, W/H, of 11.25. The test cylinder was sized such that the diameter-to-duct height ratio, D/H is 5. Results presented in this paper reveal visual and quantitative details of local fin-surface heat transfer distributions in the vicinity of a circular tube, a delta-winglet pair, and a combination of a circular tube and a delta-winglet pair. Comparisons of local and average heat transfer distributions for the circular tube with and without winglets are provided. Overall mean fin-surface Nusselt-number results indicate a significant level of heat transfer enhancement associated with the deployment of the winglets with the circular cylinder. At the lowest Reynolds numbers (which correspond to the laminar operating conditions of existing geothermal air-cooled condensers), the enhancement level is nearly a factor of 2. At higher Reynolds numbers, the enhancement level is close to 50%.

scholarly journals Friction factors and internal flow length scales of gas-solid magnetically stabilized beds in axial fields: Scaling and applications to bed-to-surface heat transfer

2005 ◽  
Vol 9 (1) ◽  
pp. 73-98 ◽  
Author(s):  
Jordan Hristov
Keyword(s):  
Heat Transfer ◽  
Scaling Law ◽  
Internal Flow ◽  
Packed Bed ◽  
Surface Heat ◽  
Length Scale ◽  
Length Scales ◽  
Surface Heat Transfer ◽  
Friction Factors ◽  
Flow Length

Friction factors and internal flow length scales of gas-solid magnetically stabilized beds are discussed. Pressure drop and expansion data of beds stabilized by axial magnetic fields are used. The concept of a variable friction factor of fluid-driven deformable packed bed is discussed. Scaling relationships of the internal flow length scale and the bed overall porosity are developed through three approaches: (1) fluidization approach concerning a length scale proportional to the particle size, (2) packed bed approach based on a hydraulic diameters as a length scale, and (3) porous media approach based on the Forchheimer equation. The main result is that the bed length scale ~e", irrespective of the model used, where n is the exponent of the Richardson-Zaki scaling law. These scaling estimates are used to explain the magnetic field effects on bed-to-surface heat transfer coefficients.

High Freestream Turbulence Effects on Endwall Heat Transfer for a Gas Turbine Stator Vane

2000 ◽  
Author(s):  
R. W. Radomsky ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Gas Turbine ◽  
Convective Heat ◽  
Leading Edge ◽  
Secondary Flows ◽  
Laser Doppler Velocimeter ◽  
Freestream Turbulence ◽  
Stator Vane ◽  
The Mean

High freestream turbulence along a gas turbine airfoil and strong secondary flows along the endwall have both been reported to significantly increase convective heat transfer. This study superimposes high freestream 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 freestream turbulence levels (0.6%) and combustor simulated turbulence levels (19.5%) 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 velocimeter (LDV) measurements were performed of all three components of the mean and fluctuating velocities of the leading edge horse-shoe vortex. The results indicate that the mean flowfields for the leading edge horseshoe vortex were similar between the low and high freestream turbulence cases. High turbulence levels in the leading edge-endwall juncture were attributed to a vortex unsteadiness for both the low and high freestream tubulence cases. While, in general, the high freestream turbulence increased the endwall heat transfer, low augmentations were found to coincide with the regions having the most intense vortex motions.

Experimental Measurements and Modeling of the Effects of Large-Scale Freestream Turbulence on Heat Transfer

2006 ◽  
Vol 129 (3) ◽  
pp. 542-550 ◽  
Author(s):  
A. C. Nix ◽  
T. E. Diller ◽  
W. F. Ng
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Turbine Blade ◽  
Large Scale ◽  
Surface Heat ◽  
Integral Length Scale ◽  
Length Scale ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Surface Heat Transfer

The influence of freestream turbulence representative of the flow downstream of a modern gas turbine combustor and first stage vane on turbine blade heat transfer has been measured and analytically modeled in a linear, transonic turbine cascade. High-intensity, large length-scale freestream turbulence was generated using a passive turbulence-generating grid to simulate the turbulence generated in modern combustors after passing through the first stage vane row. The grid produced freestream turbulence with intensity of approximately 10–12% and an integral length scale of 2cm(Λx∕c=0.15) near the entrance of the cascade passages. Mean heat transfer results with high turbulence showed an increase in heat transfer coefficient over the baseline low turbulence case of approximately 8% on the suction surface of the blade, with increases on the pressure surface of approximately 17%. Time-resolved surface heat transfer and passage velocity measurements demonstrate strong coherence in velocity and heat flux at a frequency correlating with the most energetic eddies in the turbulence flow field (the integral length scale). An analytical model was developed to predict increases in surface heat transfer due to freestream turbulence based on local measurements of turbulent velocity fluctuations and length scale. The model was shown to predict measured increases in heat flux on both blade surfaces in the current data. The model also successfully predicted the increases in heat transfer measured in other work in the literature, encompassing different geometries (flat plate, cylinder, turbine vane, and turbine blade) and boundary layer conditions.

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