Heat Transfer and Flowfield Measurements in the Leading Edge Region of a Stator Vane Endwall

1998 ◽  
Author(s):  
M. B. Kang ◽  
A. Kohli ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Leading Edge ◽  
Secondary Flows ◽  
Edge Region ◽  
Leading Edge Vortex ◽  
Lower Reynolds Number ◽  
Stator Vane ◽  
Edge Vortex ◽  
The Mean

The leading edge region of a first stage stator vane experiences high heat transfer rates especially near the end wall making it very important to get a better understanding of the formation of the leading edge vortex. In order to improve numerical predictions of the complex endwall flow, benchmark quality experimental data are required. To this purpose, this study documents the endwall heat transfer and static pressure coefficient distribution of a modern stator vane for two different exit Reynolds numbers (Reex = 6 × 105 and 1.2 × 106). In addition, laser Doppler velocimeter measurements of all three components of the mean and fluctuating velocities are presented for the stagnation plane in the leading edge region. Results indicate that the endwall heat transfer, pressure distribution and flowfield characteristics change with Reynolds number. The endwall pressure distributions show that lower pressure coefficients occur at the higher Reynolds number due to secondary flows. The stronger secondary flows cause enhanced heat transfer near the trailing edge of the vane at the higher Reynolds number. On the other hand the mean velocity, turbulent kinetic energy and vorticity results indicate that leading edge vortex is stronger and more turbulent at the lower Reynolds number. The Reynolds number also has an effect on the location of the separation point which moves closer to the stator vane at the lower Reynolds number.

Heat Transfer and Flowfield Measurements in the Leading Edge Region of a Stator Vane Endwall

1999 ◽  
Vol 121 (3) ◽  
pp. 558-568 ◽  
Author(s):  
M. B. Kang ◽  
A. Kohli ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Edge Region ◽  
Leading Edge Vortex ◽  
Stator Vane ◽  
Edge Vortex ◽  
The Mean

The leading edge region of a first-stage stator vane experiences high heat transfer rates, especially near the endwall, making it very important to get a better understanding of the formation of the leading edge vortex. In order to improve numerical predictions of the complex endwall flow, benchmark quality experimental data are required. To this purpose, this study documents the endwall heat transfer and static pressure coefficient distribution of a modern stator vane for two different exit Reynolds numbers (Reex = 6 × 105 and 1.2 × 106). In addition, laser-Doppler velocimeter measurements of all three components of the mean and fluctuating velocities are presented for a plane in the leading edge region. Results indicate that the endwall heat transfer, pressure distribution, and flowfield characteristics change with Reynolds number. The endwall pressure distributions show that lower pressure coefficients occur at higher Reynolds numbers due to secondary flows. The stronger secondary flows cause enhanced heat transfer near the trailing edge of the vane at the higher Reynolds number. On the other hand, the mean velocity, turbulent kinetic energy, and vorticity results indicate that leading edge vortex is stronger and more turbulent at the lower Reynolds number. The Reynolds number also has an effect on the location of the separation point, which moves closer to the stator vane at lower Reynolds numbers.

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 Studies and Correlations of Radially Outward and Inward Air-Flow Heat Transfer in a Rotating Square Duct

1996 ◽  
Vol 118 (1) ◽  
pp. 23-30 ◽  
Author(s):  
C. R. Kuo ◽  
G. J. Hwang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Experimental Studies ◽  
Leading Edge ◽  
Wall Heat Transfer ◽  
Square Duct ◽  
Reinforced Plastic ◽  
Flow Heat ◽  
The Mean ◽  
Heated Length

Experiments were conducted to investigate the convective heat transfer of radially outward and inward air flows in a uniformly heated rotating square duct. The interior duct surfaces, constructed by fiberglass-reinforced plastic, were plated with separated film heaters for distinguishing the local wall heat transfer rate. The duct hydraulic diameter, the actively heated length, and the mean rotation radius are 4, 120, and 180 mm, respectively. In the experiments, the parameters were the throughflow Reynolds number, Re = 1,000∼15,000; the rotation number, Ro = 0∼0.32; and the rotational buoyancy parameter, Ra* = 0∼0.5. For the outward flow the Coriolis-induced cross-stream secondary flow strongly enhanced the heat transfer on the leading edge. But for the radially inward flow the trend was reversed. When the throughflow Reynolds number was increased, the rotating-buoyancy decreased, then increased the heat transfer for the outward flow; however, the rotating-buoyancy always increased the heat transfer for the inward flow. The heat transfer data are correlated for the outward and inward flows for the ranges of parameters under study.

scholarly journals The leading-edge vortex on a rotating wing changes markedly beyond a certain central body size

2018 ◽  
Vol 5 (7) ◽  
pp. 172197 ◽  
Author(s):  
Shantanu S. Bhat ◽  
Jisheng Zhao ◽  
John Sheridan ◽  
Kerry Hourigan ◽  
Mark C. Thompson
Keyword(s):  
Reynolds Number ◽  
Body Size ◽  
Central Body ◽  
Three Dimensional ◽  
Leading Edge ◽  
Particle Image Velocimetry Technique ◽  
Leading Edge Vortex ◽  
Rapid Acquisition ◽  
Edge Vortex ◽  
Rotating Wing

Stable attachment of a leading-edge vortex (LEV) plays a key role in generating the high lift on rotating wings with a central body. The central body size can affect the LEV structure broadly in two ways. First, an overall change in the size changes the Reynolds number, which is known to have an influence on the LEV structure. Second, it may affect the Coriolis acceleration acting across the wing, depending on the wing-offset from the axis of rotation. To investigate this, the effects of Reynolds number and the wing-offset are independently studied for a rotating wing. The three-dimensional LEV structure is mapped using a scanning particle image velocimetry technique. The rapid acquisition of images and their correlation are carefully validated. The results presented in this paper show that the LEV structure changes mainly with the Reynolds number. The LEV-split is found to be only minimally affected by changing the central body radius in the range of small offsets, which interestingly includes the range for most insects. However, beyond this small offset range, the LEV-split is found to change dramatically.

scholarly journals Full Coverage Shaped-Hole Film Cooling in an Accelerating Boundary Layer With High Freestream Turbulence

2016 ◽  
Vol 138 (7) ◽  
Author(s):  
J. E. Kingery ◽  
F. E. Ames
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Density Ratio ◽  
Leading Edge ◽  
Test Surface ◽  
Turbulence Level ◽  
Full Coverage ◽  
Lower Reynolds Number ◽  
Shaped Hole

Full coverage shaped-hole film cooling and downstream heat transfer measurements have been acquired in the accelerating flows over a large cylindrical leading edge test surface. The shaped holes had an 8 deg lateral expansion angled at 30 deg to the surface with spanwise and streamwise spacings of 3 diameters. Measurements were conducted at four blowing ratios, two Reynolds numbers, and six well documented turbulence conditions. Film cooling measurements were acquired over a four to one range in blowing ratio at the lower Reynolds number and at the two lower blowing ratios for the higher Reynolds number. The film cooling measurements were acquired at a coolant to free-stream density ratio of approximately 1.04. The flows were subjected to a low turbulence (LT) condition (Tu = 0.7%), two levels of turbulence for a smaller sized grid (Tu = 3.5% and 7.9%), one turbulence level for a larger grid (8.1%), and two levels of turbulence generated using a mock aerocombustor (AC) (Tu = 9.3% and 13.7%). Turbulence level is shown to have a significant influence in mixing away film cooling coverage progressively as the flow develops in the streamwise direction. Effectiveness levels for the AC turbulence condition are reduced to as low as 20% of LT values by the furthest downstream region. The film cooling discharge is located close to the leading edge with very thin and accelerating upstream boundary layers. Film cooling data at the lower Reynolds number show that transitional flows have significantly improved effectiveness levels compared with turbulent flows. Downstream effectiveness levels are very similar to slot film cooling data taken at the same coolant flow rates over the same cylindrical test surface. However, slots perform significantly better in the near discharge region. These data are expected to be very useful in grounding computational predictions of full coverage shaped-hole film cooling with elevated turbulence levels and acceleration. Infrared (IR) measurements were performed for the two lowest turbulence levels to document the spanwise variation in film cooling effectiveness and heat transfer.

Turbine Blade Leading Edge Cooling With One Row of Normal or Tangential Impinging Jets

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Nian Wang ◽  
Andrew F. Chen ◽  
Mingjie Zhang ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Leading Edge ◽  
Jet Impingement ◽  
Test Surface ◽  
Test Model ◽  
Edge Region ◽  
Target Plate ◽  
Blade Leading Edge

Jet impingement cooling has been extensively used in the leading edge region of a gas turbine blade. This study focuses on the effect of jet impinging position on leading edge heat transfer. The test model is composed of a semicylindrical target plate, side exit slots, and an impingement jet plate. A row of cylindrical injection holes is located along the axis (normal jet) or the edge (tangential jet) of the semicylinder, on the jet plate. The jet-to-target-plate distance to jet diameter ratio (z/d) is 5 and the ratio of jet-to-jet spacing to jet diameter (s/d) is 4. The jet Reynolds number is varied from 10,000 to 30,000. Detailed impingement heat transfer coefficient distributions were experimentally measured by using the transient liquid crystal (TLC) technique. To understand the thermal flow physics, numerical simulations were performed using Reynolds-averaged Navier–Stokes (RANS) with two turbulence models: realizable k–ε (RKE) and shear stress transport k–ω model (SST). Comparisons between the experimental and the numerical results are presented. The results indicate that the local Nusselt numbers on the test surface increase with the increasing jet Reynolds number. The tangential jets provide more uniform heat transfer distributions as compared with the normal jets. For the normal jet impingement and the tangential jet impingement, the RKE model provides better prediction than the SST model. The results can be useful for selecting a jet impinging position in order to provide the proper cooling distribution inside a turbine blade leading edge region.

Effects of Reynolds number on leading-edge vortex formation dynamics and stability in revolving wings

2021 ◽  
Vol 931 ◽  
Author(s):  
Long Chen ◽  
Luyao Wang ◽  
Chao Zhou ◽  
Jianghao Wu ◽  
Bo Cheng
Keyword(s):  
Reynolds Number ◽  
Steady State ◽  
Numerical Methods ◽  
Vortex Formation ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Formation Dynamics ◽  
Edge Vortex ◽  
Vorticity Balance ◽  
Vortex Compression

The mechanisms of leading-edge vortex (LEV) formation and its stable attachment to revolving wings depend highly on Reynolds number ( $\textit {Re}$ ). In this study, using numerical methods, we examined the $\textit {Re}$ dependence of LEV formation dynamics and stability on revolving wings with $\textit {Re}$ ranging from 10 to 5000. Our results show that the duration of the LEV formation period and its steady-state intensity both reduce significantly as $\textit {Re}$ decreases from 1000 to 10. Moreover, the primary mechanisms contributing to LEV stability can vary at different $\textit {Re}$ levels. At $\textit {Re} <200$ , the LEV stability is mainly driven by viscous diffusion. At $200<\textit {Re} <1000$ , the LEV is maintained by two distinct vortex-tilting-based mechanisms, i.e. the planetary vorticity tilting and the radial–tangential vorticity balance. At $\textit {Re}>1000$ , the radial–tangential vorticity balance becomes the primary contributor to LEV stability, in addition to secondary contributions from tip-ward vorticity convection, vortex compression and planetary vorticity tilting. It is further shown that the regions of tip-ward vorticity convection and tip-ward pressure gradient almost overlap at high $\textit {Re}$ . In addition, the contribution of planetary vorticity tilting in LEV stability is $\textit {Re}$ -independent. This work provides novel insights into the various mechanisms, in particular those of vortex tilting, in driving the LEV formation and stability on low- $\textit {Re}$ revolving wings.

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