scholarly journals Vane Suction Surface Heat Transfer in Regions of Secondary Flows: The Influence of Turbulence Level, Reynolds Number, and the Endwall Boundary Condition

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Justin E. Varty ◽  
Loren W. Soma ◽  
Forrest E. Ames ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Boundary Condition ◽  
Secondary Flow ◽  
Reynolds Numbers ◽  
High Heat ◽  
Surface Heat ◽  
Secondary Flows ◽  
Suction Surface ◽  
High Heat Transfer

Secondary flows in vane passages sweep off the endwall and onto the suction surface at a location typically close to the throat. These endwall/vane junction flows often have an immediate impact on heat transfer in this region and also move any film cooling off the affected region of the vane. The present paper documents the impact of secondary flows on suction surface heat transfer acquired over a range of turbulence levels (0.7–17.4%) and a range of exit chord Reynolds numbers (500,000–2,000,000). Heat transfer data are acquired with both an unheated endwall boundary condition and a heated endwall boundary condition. The vane design includes an aft loaded suction surface and a large leading edge diameter. The unheated endwall boundary condition produces initially very high heat transfer levels due to the thin thermal boundary layer starting at the edge of heating. This unheated starting length effect quickly falls off with the thermal boundary layer growth as the secondary flow sweeps up onto the vane suction surface. The heat transfer visualization for the heated endwall condition shows no initial high heat transfer level near the edge of heating on the vane. The heat transfer level in the region affected by the secondary flows is largely uniform, except for a notable depression in the affected region. This heat transfer depression is believed due to an upwash region generated above the separation line of the passage vortex, likely in conjunction with the counter rotating suction leg of the horseshoe vortex. The extent and definition of the secondary flow-affected region on the suction surface are clearly evident at lower Reynolds numbers and lower turbulence levels when the suction surface flow is largely laminar. The heat transfer in the plateau region has a magnitude similar to a turbulent boundary layer. However, the location and extent of this secondary flow-affected region are less perceptible at higher turbulence levels where transitional or turbulent flow is present. Also, aggressive mixing at higher turbulence levels serves to smooth out discernable differences in the heat transfer due to the secondary flows.

Vane Suction Surface Heat Transfer in Regions of Secondary Flows: The Influence of Turbulence Level, Reynolds Number and the Endwall Boundary Condition

2017 ◽  
Author(s):  
J. Varty ◽  
L. W. Soma ◽  
F. E. Ames ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Boundary Condition ◽  
Secondary Flow ◽  
Reynolds Numbers ◽  
High Heat ◽  
Surface Heat ◽  
Secondary Flows ◽  
Suction Surface ◽  
High Heat Transfer

Secondary flows in vane passages sweep off the endwall and onto the suction surface at a location typically close to the throat. These endwall/vane junction flows often have an immediate impact on heat transfer in this region and also move any film cooling off the affected region of the vane. The present paper documents the impact of secondary flows on suction surface heat transfer acquired over a range of turbulence levels (0.7% through 17.4%) and a range of exit chord Reynolds numbers (500,000 through 2,000,000). Heat transfer data are acquired with both an unheated endwall boundary condition and a heated endwall boundary condition. The vane design includes an aft loaded suction surface and a large leading edge diameter. The unheated endwall boundary condition produces initially very high heat transfer levels due to the thin thermal boundary layer starting at the edge of heating. This unheated starting length effect quickly falls off with the thermal boundary layer growth as the secondary flow sweeps up onto the vane suction surface. The heat transfer visualization for the heated endwall condition shows no initial high heat transfer level near the edge of heating on the vane. The heat transfer level in the region affected by the secondary flows is largely uniform, except for a notable depression in the affected region. This heat transfer depression is believed due to an upwash region generated above the separation line of the passage vortex, likely in conjunction with the counter rotating suction leg of the horseshoe vortex. The extent and definition of the secondary flow affected region on the suction surface is clearly evident at lower Reynolds numbers and lower turbulence levels when the suction surface flow is largely laminar. The heat transfer in the plateau region has a magnitude similar to a turbulent boundary layer. However, the location and extent of this secondary flow affected region is less perceptible at higher turbulence levels where transitional or turbulent flow is present. Also, aggressive mixing at higher turbulence levels serves to smooth out discernable differences in the heat transfer due to the secondary flows.

The Effects of Localized Blade Endwall Suction on Secondary Flows and Heat Transfer

2010 ◽  
Author(s):  
Rebecca Hollis ◽  
Jeffrey P. Bons
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
High Surface ◽  
Surface Heat ◽  
Secondary Flows ◽  
Surface Shear Stress ◽  
Mean Velocity ◽  
Surface Shear ◽  
Surface Heat Transfer ◽  
High Heat Transfer

Two methods of flow control were designed to mitigate the effects of the horseshoe vortex structure (HV) at an airfoil/endwall junction. An experimental study was conducted to quantify the effects of localized boundary layer removal on surface heat transfer in a low-speed wind tunnel. A transient infrared technique was used to measure the convective heat transfer values along the surface surrounding the juncture. Particle image velocimetry was used to collect the time-mean velocity vectors of the flow field across three planes of interest. Boundary layer suction was applied through a thin slot cut into the leading edge of the airfoil at two locations. The first, referred to as Method 1, was directly along the endwall, the second, Method 2, was located at a height ∼1/3 of the approaching boundary layer height. Five suction rates were tested; 0%, 6.5%, 11%, 15% and 20% of the approaching boundary layer mass flow was removed at a constant rate. Both methods reduced the effects of the HV with increasing suction on the symmetry, 0.5-D and 1-D planes. Method 2 yielded a greater reduction in surface heat transfer but Method 1 outperformed Method 2 aerodynamically by completely removing the HV structure when 11% suction was applied. This method however produced other adverse effects such as high surface shear stress and localized areas of high heat transfer near the slot edges at high suction rates.

An Experimental Study of Heat Transfer in a Large-Scale Turbine Rotor Passage

1992 ◽  
Author(s):  
Michael F. Blair
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Large Scale ◽  
Leading Edge ◽  
High Heat ◽  
Turbine Rotor ◽  
Secondary Flows ◽  
Suction Surface ◽  
Tip Leakage ◽  
High Heat Transfer

An experimental study of the heat transfer distribution in a turbine rotor passage was conducted in a large–scale, ambient temperature, rotating turbine model. Meat transfer was measured for both the full–span suction and pressure surfaces of the airfoil as well as for the hub endwall surface. The objective of this program was to document the effects of flow three–dimensionality on the heat transfer in a rotating blade row (vs. a stationary cascade). Of particular interest were the effects of the hub and tip secondary flows, tip leakage and the leading–edge horseshoe vortexsystem. The effect of surface roughness on the passage heat transfer was also investigated. Midspan results are compared with both smooth–wall and rough–wall finite–difference two dimensional heat transfer predictions. Contour maps of Stanton number for both the rotor airfoil and endwall surfaces revealed numerous regions of high heat transfer produced by the three dimensional flows within the rotor passage. Of particular importance are regions of local enhancement (as much as 100% over midspan values) produced on the airfoil suction surface by the secondary flows and tip–leakage vortices and on the hub endwall by the leading–edge horseshoe vortex system.

Heat Transfer for a Turbine Blade With Nonaxisymmetric Endwall Contouring

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Stephen P. Lynch ◽  
Narayan Sundaram ◽  
Karen A. Thole ◽  
Atul Kohli ◽  
Christopher Lehane
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Three Dimensional ◽  
High Heat ◽  
Secondary Flows ◽  
Flow Strength ◽  
Pressure Losses ◽  
High Heat Transfer ◽  
Oil Flow ◽  
Transfer Benefit

Complex vortical secondary flows that are present near the endwall of an axial gas turbine blade are responsible for high heat transfer rates and high aerodynamic losses. The application of nonaxisymmetric, three-dimensional contouring to the endwall surface has been shown to reduce the strength of the vortical flows and decrease total pressure losses when compared with a flat endwall. The reduction in secondary flow strength with nonaxisymmetric contouring might also be expected to reduce endwall heat transfer. In this study, measurements of endwall heat transfer were taken for a low-pressure turbine blade geometry with both flat and three-dimensional contoured endwalls. Endwall oil flow visualization indicated a reduction in the passage vortex strength for the contoured endwall geometry. Heat transfer levels were reduced by 20% in regions of high heat transfer with the contoured endwall, as compared with the flat endwall. The heat transfer benefit of the endwall contour was not affected by changes in the cascade Reynolds number.

The Thickness of the Liquid Microlayer Between a Cap-Shaped Sliding Bubble and a Heated Wall: Experimental Measurements

2006 ◽  
Vol 128 (9) ◽  
pp. 934-944 ◽  
Author(s):  
Xin Li ◽  
D. Keith Hollingsworth ◽  
Larry C. Witte
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
High Heat ◽  
Heated Wall ◽  
Transfer Coefficients ◽  
Data Set ◽  
Laser Probe ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Spherical Bubbles

A laser-based method has been developed to measure the thickness of the liquid microlayer between a cap-shaped sliding bubble and an inclined heated wall. Sliding vapor bubbles are known to create high heat transfer coefficients along the surfaces against which they slide. The details of this process remain unclear and depend on the evolution of the microlayer that forms between the bubble and the surface. Past experiments have used heat transfer measurements on uniform-heat-generation surfaces to infer the microlayer thickness through an energy balance. These studies have produced measurements of 20–100 μm for refrigerants and for water, but they have yet to be confirmed by a direct measurement that does not depend on a first-law closure. The results presented here are direct measurements of the microlayer thickness made from a reflectance-based fiber-optic laser probe. Details of the construction and calibration of the probe are presented. Data for saturated FC-87 and a uniform-temperature surface inclined at 2 deg to 15 deg from the horizontal are reported. Millimeter-sized spherical bubbles of FC-87 vapor were injected near the lower end of a uniformly heated aluminum plate. The laser probe yielded microlayer thicknesses of 22–55 μm for cap-shaped bubbles. Bubble Reynolds numbers range from 600 to 4800, Froude numbers from 0.9 to 1.7, and Weber numbers from 2.6 to 47. The microlayer thickness above cap-shaped bubbles was correlated to a function of inclination angle and a bubble shape factor. The successful correlation suggests that this data set can be used to validate the results of detailed models of the microlayer dynamics.

Influence of Discrete Pin Shaped Surface Roughness (P-Pins) on Heat Transfer and Aerodynamics of Film Cooled Aerofoil

2002 ◽  
Author(s):  
S. M. Guo ◽  
M. L. G. Oldfield ◽  
A. J. Rawlinson
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Surface Roughness ◽  
Turbine Blades ◽  
Thermodynamic Characteristics ◽  
Wide Band ◽  
Reynolds Numbers ◽  
Suction Surface ◽  
Shaped Surface ◽  
Annular Cascade

The influence of localized pin-shaped surface roughness (P-Pins) on heat transfer and aerodynamics of a fully film cooled engine aerofoil has been studied in a transonic annular cascade. The “P-Pins”, present on some casting film cooled turbine blades and vanes, are the residues left in the manufacturing process. This paper investigates the effect of the P-Pins on the aerodynamic performance and measures the heat transfer consequences both for the aerofoils and the P-Pins. The effect on performance was determined independently on the pressure and suction surface of the aerofoil. For comparison, the aerofoil without P-Pins was also tested to provide baseline results. The measurements have been made at engine representative Mach and Reynolds numbers. Wide band liquid crystal and direct heat flux gauge technique were employed in the heat transfer tests. A four-hole pyramid probe was used to obtain the aerodynamic data. The aerodynamic and thermodynamic characteristics of the coolant flow have been modelled to represent engine conditions by using a heavy “foreign gas” (30.2% SF6 and 69.8% Ar by weight). The paper concludes that P-Pins as usually placed on the blade do not have detrimental effects to the heat transfer performance of film-cooled aerofoil. P-Pins, located in thick boundary layer regions of the aerofoil, such as the later portion of the suction surface, do not cause any reduction of aerofoil aerodynamic efficiency. For contrast, the P-Pins located in the thin boundary layer regions on the pressure side of the aerofoil cause noticeably more losses.

Transient Leading to Periodic Fluid Flow and Heat Transfer in a Differentially-Heated Cavity Due to an Insulated Rotating Object

2007 ◽  
Author(s):  
Y.-C. Shih ◽  
J. M. Khodadadi ◽  
K.-H. Weng ◽  
H. F. Oztop
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
High Heat ◽  
Thermal Fields ◽  
Flow And Heat Transfer ◽  
High Heat Transfer ◽  
Transient Variations ◽  
Rotating Objects

Computational analysis of transient phenomenon followed by the periodic state of laminar flow and heat transfer due to an insulated rotating object in a square cavity is investigated. A finite-volume-based computational methodology utilizing primitive variables is used. Various rotating objects (circle, square and equilateral triangle) with different sizes are placed in the middle of the cavity. A combination of a fixed computational grid with a sliding mesh was utilized for the square and triangle shapes. The cavity is maintained as a differentially-heated enclosure and the motionless insulated object is set in rotation at time t = 0. Natural convection heat transfer is neglected. For a given shape of the object and a constant angular velocity, a range of rotating Reynolds numbers are covered for a Pr = 5 fluid. The Reynolds numbers were selected so that the flow fields are not generally affected by the Taylor instabilities (Ta < 1750). The evolving flow field and the interaction of the rotating objects with the recirculating vortices at the four corners are elucidated. The corresponding thermal fields in relation to the evolving flow patterns and the skewness of the temperature contours in comparison to conduction-only case were discussed. The skewness is observed to become more marked as the Reynolds number is lowered. At the same time, similarity of the thermal fields for various shapes for the same Reynolds number varifies the appropriate selection of the hydraulic diameter. Transient variations of the average Nusselt numbers on the two walls show that for high Re numbers, a quasi-periodic behavior due to the onset of the Taylor instabilities is dominant, whereas for low Re numbers, periodicity of the system is clearly observed. Time-integrated average Nusselt number of the cavity is correlated to the rotational Reynolds number and shape of the object. The triangle object clearly gives rise to high heat transfer followed by the square and circle objects.

Heat Transfer of Winglet Tips in a Transonic Turbine Cascade

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Fangpan Zhong ◽  
Chao Zhou ◽  
H. Ma ◽  
Q. Zhang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Suction Side ◽  
High Heat ◽  
Suction Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
High Heat Transfer ◽  
The Heat Transfer Coefficient

Understanding the heat transfer of winglet tips is crucial for their applications in high-pressure turbines. The current paper investigates the heat transfer performance of three different winglet-cavity tips in a transonic turbine cascade at a tip gap of 2.1% chord. A cavity tip is studied as the baseline case. The cascade operates at engine representative conditions of an exit Mach number of 1.2 and an exit Reynolds number of 1.7 × 106. Transient infrared thermography technique was used to obtain the tip distributions of heat transfer coefficient for different tips in the experiment. The CFD results were validated with the measured tip heat transfer coefficients, and then used to explain the flow physics related to heat transfer. It is found that on the pressure side winglet, the flow reattaches on the top winglet surface and results in high heat transfer coefficient. On the suction side winglet, the heat transfer coefficient is low near the blade leading edge but is higher from the midchord to the trailing edge. The suction side winglet pushes the tip leakage vortex further away from the blade suction surface and reduces the heat transfer coefficient from 85% to 96% span on the blade suction surface. However, the heat transfer coefficient is higher for the winglet tips from 96% span to the tip. This is because the tip leakage vortex attaches on the side surface of the suction side winglet and results in quite high heat transfer coefficient on the front protrusive part of the winglet. The effects of relative endwall motion between the blade tip and the casing were investigated by CFD method. The endwall motion has a significant effect on the flow physics within the tip gap and near-tip region in the blade passage, thus affects the heat transfer coefficient distributions. With relative endwall motion, a scraping vortex forms inside the tip gap and near the casing, and the cavity vortex gets closer to the pressure side squealer/winglet. The tip leakage vortex in the blade passage becomes closer to the blade suction surface, resulting in an increase of the heat transfer coefficient.

Flowfield Measurements in the Endwall Region of a Stator Vane

1999 ◽  
Author(s):  
M. B. Kang ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Suction Side ◽  
Secondary Flows ◽  
Laser Doppler Velocimeter ◽  
Transfer Coefficients ◽  
Suction Surface ◽  
Numerical Predictions ◽  
High Heat Transfer ◽  
Passage Vortex ◽  
Stator Vane

A first stage stator vane experiences high heat transfer rates particularly near the end wall where strong secondary flows occur. In order to improve numerical predictions of the complex endwall flow at low speed conditions, benchmark quality experimental data are required. This study documents the flowfield in the endwall region of a stator vane that has been scaled up by a factor of nine while matching an engine exit Reynolds number of Reex = 1.2·106. Laser Doppler velocimeter (LDV) measurements of all three components of the mean and fluctuating velocities are presented for several flow planes normal to the turbine vane. Measurements indicate that downstream of the minimum static pressure location on the suction surface of the vane, an attenuated suction side leg of the horseshoe vortex still exists. At this location, the peak turbulent kinetic energy coincides with the center of the passage vortex location. These flowfield measurements were also related to previously reported convective heat transfer coefficients on the endwall showing that high Stanton numbers occur where the passage vortex brings mainstream fluid towards the vane surface.

Winglets for Improved Aerothermal Performance of High Pressure Turbines

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
John D. Coull ◽  
Nick R. Atkins ◽  
Howard P. Hodson
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Three Dimensional ◽  
Leading Edge ◽  
High Heat ◽  
Operating Conditions ◽  
Leakage Flow ◽  
Suction Surface ◽  
Wall Flows ◽  
High Heat Transfer

This paper investigates the design of winglet tips for unshrouded high pressure turbine rotors considering aerodynamic and thermal performance simultaneously. A novel parameterization method has been developed to alter the tip geometry of a rotor blade. A design survey of uncooled, flat-tipped winglets is performed using Reynolds-averaged Navier–Stokes (RANS) calculations for a single rotor at engine representative operating conditions. Compared to a plain tip, large efficiency gains can be realized by employing an overhang around the full perimeter of the blade, but the overall heat load rises significantly. By employing an overhang on only the early suction surface, significant efficiency improvements can be obtained without increasing the overall heat transfer to the blade. The flow physics are explored in detail to explain the results. For a plain tip, the leakage and passage vortices interact to create a three-dimensional impingement onto the blade suction surface, causing high heat transfer. The addition of an overhang on the early suction surface displaces the tip leakage vortex away from the blade, weakening the impingement effect and reducing the heat transfer on the blade. The winglets reduce the aerodynamic losses by unloading the tip section, reducing the leakage flow rate, turning the leakage flow in a more streamwise direction, and reducing the interaction between the leakage fluid and end wall flows. Generally, these effects are most effective close to the leading edge of the tip where the leakage flow is subsonic.

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