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.

Winglets for Improved Aerothermal Performance of High Pressure Turbines

2013 ◽  
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 ◽  
High Heat Transfer ◽  
Leakage Flow Rate

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 un-cooled, flat-tipped winglets is performed using 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 endwall flows. Generally these effects are most effective close to the leading edge of the tip, where the leakage flow is subsonic.

Analysis of Flow and Heat Transfer in the End-Wall Region of a Turbine Blade Passage

2000 ◽  
Author(s):  
Yumin Xiao ◽  
R. S. Amano
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
High Heat ◽  
Wall Region ◽  
Trailing Edge ◽  
High Heat Transfer ◽  
Transfer Region ◽  
End Wall

A numerical study has been performed to predict a three-dimensional turbulent flow and end-wall heat transfer in a blade passage. The complex three-dimensional flow in the end-wall region has an important impact on the local heat transfer. The leading edge horseshoe vortex, the leading edge corner vortices, the passage vortex, and the trailing edge wake cause large variations in the entire end-wall region. The heat transfer distributions in the end-wall region are calculated and the mechanism for the high heat transfer region has been revealed. The calculations show that the algebraic turbulence model lacks the ability to predict the heat transfer in the transition region, but it is valid in other flow region. The local high heat transfer downstream of the trailing edge is enhanced by the wake downstream of the trailing edge. The horseshoe vortex results a high heat transfer region near the leading edge and induces the leading edge corner vortices which cause high heat transfer on the end-wall at both sides of blade end-wall corner.

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.

Numerical Simulation of Gas Flow and Heat Transfer in Cross-Wavy Primary Surface Channel for Microtubine Recuperators

2005 ◽  
Author(s):  
H. X. Liang ◽  
Q. W. Wang ◽  
L. Q. Luo ◽  
Z. P. Feng
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Gas Turbine ◽  
Numerical Study ◽  
High Reliability ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Flow And Heat Transfer ◽  
High Heat Transfer ◽  
The Cross

Three-dimensional numerical simulation was conducted to investigate the flow field and heat transfer performance of the Cross-Wavy Primary Surface (CWPS) recuperators for microturbines. Using high-effective compact recuperators to achieve high thermal efficiency is one of the key techniques in the development of microturbine in recent years. Recuperators need to have minimum volume and weight, high reliability and durability. Most important of all, they need to have high thermal-effectiveness and low pressure-losses so that the gas turbine system can achieve high thermal performances. These requirements have attracted some research efforts in designing and implementing low-cost and compact recuperators for gas turbine engines recently. One of the promising techniques to achieve this goal is the so-called primary surface channels with small hydraulic dimensions. In this paper, we conducted a three-dimensional numerical study of flow and heat transfer for the Cross-Wavy Primary Surface (CWPS) channels with two different geometries. In the CWPS configurations the secondary flow is created by means of curved and interrupted surfaces, which may disturb the thermal boundary layers and thus improve the thermal performances of the channels. To facilitate comparison, we chose the identical hydraulic diameters for the above four CWPS channels. Since our experiments on real recuperators showed that the Reynolds number ranges from 150 to 500 under the operating conditions, we implemented all the simulations under laminar flow situations. By analyzing the correlations of Nusselt numbers and friction factors vs. Reynolds numbers of the four CWPS channels, we found that the CWPS channels have superior and comprehensive thermal performance with high compactness, i.e., high heat transfer area to volume ratio, indicating excellent commercialized application in the compact recuperators.

Heat Transfer and Aerodynamics of Over-Shroud Leakage Flows in a High-Pressure Turbine

2009 ◽  
Author(s):  
Knut Lehmann ◽  
Richard Thomas ◽  
Howard Hodson ◽  
Vassilis Stefanis
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Large Scale ◽  
Suction Side ◽  
Surface Flow ◽  
Tip Clearance ◽  
Flow Visualisation ◽  
Leakage Flow ◽  
High Pressure Turbine ◽  
High Heat Transfer

An experimental study has been conducted to investigate the distribution of the convective heat transfer on the shroud of a high pressure turbine blade in a large scale rotating rig. A continuous thin heater foil technique has been adapted and implemented on the turbine shroud. Thermochromic Liquid Crystals were employed for the surface temperature measurements to derive the experimental heat transfer data. The heat transfer is presented on the shroud top surfaces and the three fins. The experiments were conducted for a variety of Reynolds numbers and flow coefficients. The effects of different inter-shroud gap sizes and reduced fin tip clearance gaps were also investigated. Details of the shroud flow field were obtained using an advanced Ammonia-Diazo surface flow visualisation technique. CFD predictions are compared with the experimental data and used to aid interpretation. Contour maps of the Nusselt number reveal that regions of highest heat transfer are mostly confined to the suction side of the shroud. Peak values exceed the average by as much as 100 percent. It has been found that the interaction between leakage flow through the inter-shroud gaps and the fin tip leakage jets are responsible for this high heat transfer. The inter-shroud gap leakage flow causes a disruption of the boundary layer on the turbine shroud. Furthermore, the development of the large recirculating shroud cavity vortices is severely altered by this leakage flow.

scholarly journals A Three-Dimensional Coupled Internal/External Simulation of a Film-Cooled Turbine Vane

1999 ◽  
Author(s):  
James D. Heidmann ◽  
David L. Rigby ◽  
Ali A. Ameri
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Film Cooling ◽  
Three Dimensional ◽  
High Heat ◽  
Operating Conditions ◽  
High Heat Flux ◽  
Nasa Lewis Research ◽  
Turbine Vane ◽  
Film Cooling Holes

A three-dimensional Navier-Stokes simulation has been performed for a realistic film-cooled turbine vane using the LeRC-HT code. The simulation includes the flow regions inside the coolant plena and film cooling holes in addition to the external flow. The vane is the subject of an upcoming NASA Lewis Research Center experiment and has both circular cross-section and shaped film cooling holes. This complex geometry is modeled using a multi-block grid which accurately discretizes the actual vane geometry including shaped holes. The simulation matches operating conditions for the planned experiment and assumes periodicity in the spanwise direction on the scale of one pitch of the film cooling hole pattern. Two computations were performed for different isothermal wall temperatures, allowing independent determination of heat transfer coefficients and film effectiveness values. The results indicate separate localized regions of high heat flux in the showerhead region due to low film effectiveness and high heat transfer coefficient values, while the shaped holes provide a reduction in heat flux through both parameters. Hole exit data indicate rather simple skewed profiles for the round holes, but complex profiles for the shaped holes with mass fluxes skewed strongly toward their leading edges.

Clocking Effects of Inlet Non-Uniformities in a Fully Cooled High-Pressure Vane: A Conjugate Heat Transfer Analysis

2015 ◽  
Author(s):  
Duccio Griffini ◽  
Massimiliano Insinna ◽  
Simone Salvadori ◽  
Francesco Martelli
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Film Cooling ◽  
Conjugate Heat Transfer ◽  
Cooling System ◽  
Hot Spot ◽  
Three Dimensional ◽  
Leading Edge ◽  
Suction Side ◽  
Heat Transfer Analysis

A high-pressure vane equipped with a realistic film-cooling configuration has been studied. The vane is characterized by the presence of multiple rows of fan-shaped holes along pressure and suction side while the leading edge is protected by a showerhead system of cylindrical holes. Steady three-dimensional Reynolds-Averaged Navier-Stokes (RANS) simulations have been performed. A preliminary grid sensitivity analysis with uniform inlet flow has been used to quantify the effect of spatial discretization. Turbulence model has been assessed in comparison with available experimental data. The effects of the relative alignment between combustion chamber and high-pressure vanes are then investigated considering realistic inflow conditions in terms of hot spot and swirl. The inlet profiles used are derived from the EU-funded project TATEF2. Two different clocking positions are considered: the first one where hot spot and swirl core are aligned with passage and the second one where they are aligned with the leading edge. Comparisons between metal temperature distributions obtained from conjugate heat transfer simulations are performed evidencing the role of swirl in determining both the hot streak trajectory within the passage and the coolant redistribution. The leading edge aligned configuration is resulted to be the most problematic in terms of thermal load, leading to increased average and local vane temperature peaks on both suction side and pressure side with respect to the passage aligned case. A strong sensitivity of both injected coolant mass flow and heat removed by heat sink effect has also been highlighted for the showerhead cooling system.

Feasibility Study on Application of a Self-Formed Flow Field Downstream of Elbows to Divertor Cooling

2013 ◽  
Author(s):  
Shoichi Kodate ◽  
Tatsuya Kubo ◽  
Shinji Ebara ◽  
Hidetoshi Hashizume
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Reynolds Stress ◽  
Swirling Flow ◽  
Pipe Wall ◽  
Three Dimensional ◽  
High Heat ◽  
Turbulent Pipe Flow ◽  
High Heat Transfer ◽  
Piv Measurement

In this study, the characteristic of the swirling flow was analyzed in detail in terms of flow field by means of a visualization experiment using matched refractive index PIV measurement to evaluate the applicability of the swirling flow generated downstream of a three-dimensionally connected dual elbow to the divertor cooling. The dual elbow used in the experiment comprises two 90-degree elbows with the same curvature connected directly in three-dimensional configuration. From the experiment, it was found that strong swirling velocity component appears locally near the pipe wall downstream of the second elbow. Moreover, although the strength of the swirling flow changed gradually as it flowed downstream, it attenuated little even 8D downstream of the dual elbow, where D was the diameter of the piping. Therefore, this swirling flow is expected to survive for a considerable distance downstream of the elbow, and the applicability of this flow field to divertor cooling can be promising. Furthermore turbulence quantities such as Reynolds stress were analyzed in terms of heat transfer performance. Since there were some regions where larger Reynolds stress than a developed turbulent pipe flow was observed near the pipe wall, high heat transfer is expected there.

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.

Spatial and Temporal Wall Temperature Fluctuations in Two-Phase Flow in Microgap Coolers

2010 ◽  
Author(s):  
Jessica Sheehan ◽  
Avram Bar-Cohen
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Volumetric Cooling ◽  
Very High

Heat transfer to an evaporating refrigerant and/or dielectric liquid in a microgap channel can provide very high heat transfer coefficients and volumetric cooling rates. Recent studies at Maryland have established the dominance of the annular flow regime in such microgap channels and related the observed high-quality peak of an M-shaped heat transfer coefficient curve to the onset of local dryout. The present study utilizes infrared thermography to locate such nascent dryout regions and operating conditions. Data obtained with a 210 micron microgap channel, operated with a mass flux of 195.2 kg/m2-s and heat fluxes of 10.3 to 26 W/cm2 are presented and discussed.

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