Analysis of the Unsteady Overtip Casing Heat Transfer in a High Speed Turbine

2012 ◽  
Author(s):  
S. Lavagnoli ◽  
G. Paniagua ◽  
C. De Maesschalck ◽  
T. Yasa
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Wall Temperature ◽  
Convective Heat Transfer Coefficient ◽  
Tip Clearance ◽  
Heat Flux Sensor ◽  
Flow Temperature ◽  
Local Flow ◽  
Essential Information ◽  
Transfer Pressure

In modern gas turbine engines, the rotor casing is vulnerable to thermal failures due to large unsteady heat fluxes. The rotor tip flow unsteadiness is induced by the periodic passage of the rotor blades, with an intensity dependent on the tip gap geometry. Hence, the understanding of the physics is of paramount importance to develop appropriate predictive tools and improve the cooling schemes. The present research aims at providing essential information on the flow conditions, which should serve to assess the relative impact of the overtip flow, tip gap magnitude and work extraction processes on the casing thermal load. This paper presents simultaneous measurements of steady and unsteady heat transfer, pressure and rotor tip clearance in the casing of a transonic turbine stage. The research article was tested in a compression tube facility operating at engine representative conditions (vane Mach number 1.07, vane outlet Reynolds number 1.3×106, pressure ratio is 2.92, at 6790 RPM). The rotor blade geometry has a flat tip with a nominal tip clearance of about 0.4% of blade height. The heat transfer, pressure, and tip clearance data were obtained at three circumferential positions around the turbine casing. The heat flux was monitored using a single-layered thin film gauge able to resolve with high-fidelity the wall temperature fluctuations. The heat flux sensor was mounted on a probe equipped with a heating device that allows varying the wall temperature. A series of experiments was performed at different heating rates to derive the local adiabatic wall temperature and the adiabatic convective heat transfer coefficient. A high bandwidth capacitive sensor provided the instantaneous value of the single blade tip clearance. A simple zero-dimensional model has been proved effective to predict the local flow temperature while the rotor spins up prior to the test, and estimate the overtip flow temperature during a test.

Analysis of the Unsteady Overtip Casing Heat Transfer in a High Speed Turbine

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
S. Lavagnoli ◽  
G. Paniagua ◽  
C. De Maesschalck ◽  
T. Yasa
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Wall Temperature ◽  
Convective Heat Transfer Coefficient ◽  
Tip Clearance ◽  
Heat Flux Sensor ◽  
Flow Temperature ◽  
Local Flow ◽  
Essential Information ◽  
Transfer Pressure

In modern gas turbine engines, the rotor casing is vulnerable to thermal failures due to large unsteady heat fluxes. The rotor tip flow unsteadiness is induced by the periodic passage of the rotor blades, with an intensity dependent on the tip gap geometry. Hence, the understanding of the physics is of paramount importance to develop appropriate predictive tools and improve the cooling schemes. The present research aims at providing essential information on the flow conditions, which should serve to assess the relative impact of the overtip flow, tip gap magnitude, and work extraction processes on the casing thermal load. This paper presents simultaneous measurements of steady and unsteady heat transfer, pressure and rotor tip clearance in the casing of a transonic turbine stage. The research article was tested in a compression tube facility operating at engine representative conditions (vane Mach number 1.07, vane outlet Reynolds number 1.3 × 106, pressure ratio is 2.92, at 6790 rpm). The rotor blade geometry has a flat tip with a nominal tip clearance of about 0.4% of blade height. The heat transfer, pressure, and tip clearance data were obtained at three circumferential positions around the turbine casing. The heat flux was monitored using a single-layered thin film gauge able to resolve with high fidelity the wall temperature fluctuations. The heat flux sensor was mounted on a probe equipped with a heating device that allows varying the wall temperature. A series of experiments was performed at different heating rates to derive the local adiabatic wall temperature and the adiabatic convective heat transfer coefficient. A high bandwidth capacitive sensor provided the instantaneous value of the single blade tip clearance. A simple zero-dimensional model has been proved effective to predict the local flow temperature while the rotor spins up prior to the test, and estimate the overtip flow temperature during a test.

Analysis of the Heat Transfer Driving Parameters in Tight Rotor Blade Tip Clearances

2014 ◽  
Author(s):  
S. Lavagnoli ◽  
C. De Maesschalck ◽  
G. Paniagua
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Wall Temperature ◽  
Convective Heat Transfer Coefficient ◽  
Tip Clearance ◽  
Adiabatic Wall ◽  
Engine Operation ◽  
Flow Parameters

Turbine rotor tips and casings are vulnerable to mechanical failures due to the extreme thermal loads they undergo during engine operation. In addition to the heat flux variations during the transient phase, high-frequency unsteadiness occurs at every rotor passage, with amplitude dependent on the tip gap. The development of appropriate predictive tools and cooling schemes requires the precise understanding of the heat transfer mechanisms. The present paper analyzes the nature of the overtip flow in transonic turbine rotors running at tight clearances, and explores a methodology to determine the relevant flow parameters that model the heat transfer. Steady-state three-dimensional Reynolds-Averaged Navier-Stokes calculations were performed to simulate engine-like conditions considering two rotor tip gaps, 0.1% and 1% of the blade span. At tight tip clearance, the adiabatic wall temperature is not anymore independent of the solid thermal boundary conditions. The adiabatic wall temperature predicted with the linear Newton’s cooling law was observed to rise to non-physical levels in certain regions within the rotor tip gap, resulting in unreliable convective heat transfer coefficients. This paper investigates different approaches to estimate the relevant flow parameters that drive the heat transfer. The present study allows experimentalists to retrieve information on the gap flow temperature and convective heat transfer coefficient based on the use of wall heat flux measurements. Such approach is required to improve the accuracy in the evaluation of the heat transfer data while enhancing the understanding of tight-clearance overtip flows.

On Selection of Reference Temperature of Heat Transfer Coefficient for Complicated Flows

2007 ◽  
Author(s):  
X. C. Li ◽  
J. Zhou ◽  
K. Aung
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Surface Temperature ◽  
Transfer Coefficient ◽  
Wall Temperature ◽  
Convective Heat Transfer Coefficient ◽  
Internal Heat ◽  
Reference Temperature ◽  
The Heat Transfer Coefficient

One of the most fundamental concepts in heat transfer is the convective heat transfer coefficient, which is closely related with the flow Reynolds number, flow geometry and the thermal conditions on the heat transfer surface. To define the heat transfer coefficient, a reference temperature is needed besides the surface temperature and heat flux. The reference temperature can be chosen differently, such as the fluid bulk mean temperature (for internal flows) and the temperature at the far field (for external flows). For complicated flows, the adiabatic wall temperature, defined as the wall temperature when the surface heat flux is zero, is commonly adopted as the reference temperature. Other options can also be applied to complicated flows. This paper analyzed some of the potential selections of the reference temperature for different flow settings, including film cooling, jet impingement with cross flows and a mixing flow in a straight duct with or without internal heat source. Both laminar and turbulent flows are considered with different boundary conditions. Dramatic changes of heat transfer coefficient are observed with different reference temperatures. In some special conditions the heat transfer coefficient becomes negative, which means the heat flux has a different direction with the driving temperature difference defined. An innovative method is proposed to calculate the heat transfer coefficient of complicated flows with constant surface temperature.

Experimental Characterization of the Vane Heat Flux Under Pulsating Trailing-Edge Blowing

2016 ◽  
Author(s):  
J. Saavedra ◽  
G. Paniagua ◽  
B. H. Saracoglu
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Shock Wave ◽  
Heat Flux ◽  
Wall Temperature ◽  
Separation Bubble ◽  
Convective Heat Transfer Coefficient ◽  
Trailing Edge ◽  
Power Extraction ◽  
The Impact

The steady improvement of aircraft engine performance has led towards more compact engine cores with increased structural loads. Compact single-stage high-pressure turbines allow high power extraction, operating in the low supersonic range. The shock waves formed at the airfoil trailing edge contribute substantially to turbine losses, mainly due to the shock-boundary layer interactions as well as high-frequency forces on the rotor. We propose to control the vane trailing edge shock interaction with the downstream rotor, using a pulsating vane-trailing-edge-coolant at the rotor passing frequency. A linear cascade of transonic vanes was investigated at different Mach numbers, ranging from subsonic to supersonic regimes (0.8, 1.1) at two engine representative Reynolds numbers (4 and 6 million). The steady and unsteady heat flux was retrieved using thin-film 2-layered gauges. The complexity of the tests required the development of an original heat transfer post-processing approach. In a single test, monitoring the heat flux data and the wall temperature we obtained the adiabatic wall temperature and the convective heat transfer coefficient. The right-running trailing edge shock wave impacts on the neighboring vane suction side. The impact of the shock wave on the boundary layer creates a separation bubble, which is very sensitive to the intensity and angle of the shock wave. Increasing the coolant blowing rate induces the shock to be less oblique, moving the separation bubble upstream. A similar effect is caused by the pulsations of the coolant.

Analysis of the Heat Transfer Driving Parameters in Tight Rotor Blade Tip Clearances

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Sergio Lavagnoli ◽  
Cis De Maesschalck ◽  
Guillermo Paniagua
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Wall Temperature ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Transfer Coefficients ◽  
Adiabatic Wall ◽  
Flow Parameters

Turbine rotor tips and casings are vulnerable to mechanical failures due to the extreme thermal loads they undergo during engine service. In addition to the heat flux variations during the engine transient operation, periodic unsteadiness occurs at every rotor passage, with amplitude dependent on the tip gap. The development of appropriate predictive tools and cooling schemes requires the precise understanding of the heat transfer mechanisms. The present paper analyses the nature of the overtip flow in transonic turbine rotors running at tight clearances and explores a methodology to determine the relevant flow parameters that model the heat transfer. Steady-state three-dimensional Reynolds-averaged Navier–Stokes (RANS) calculations were performed to simulate engine-like conditions considering two rotor tip gaps, 0.1% and 1%, of the blade span. At tight tip clearance, the adiabatic wall temperature is no longer independent of the solid thermal boundary conditions. The adiabatic wall temperature predicted with the linear Newton's cooling law was observed to rise to unphysical levels in certain regions within the rotor tip gap, resulting in unreliable convective heat transfer coefficients (HTCs). This paper investigates different approaches to estimate the relevant flow parameters that drive the heat transfer. A novel four-coefficient nonlinear cooling law is proposed to model the effects of temperature-dependent gas properties and of the heat transfer history. The four-parameter correlation provided reliable estimates of the convective heat transfer descriptors for the 1% tip clearance case, but failed to model the tip heat transfer of the 0.1% tip gap rotor. The present study allows experimentalists to retrieve information on the gap flow temperature and convective HTC based on the use of wall heat flux measurements. The use of nonlinear cooling laws is sought to improve the evaluation of the rotor heat transfer data while enhancing the understanding of tight-clearance overtip flows.

Experimental Characterization of the Vane Heat Flux Under Pulsating Trailing-Edge Blowing

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
J. Saavedra ◽  
G. Paniagua ◽  
B. H. Saracoglu
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Shock Wave ◽  
Heat Flux ◽  
Wall Temperature ◽  
Separation Bubble ◽  
Convective Heat Transfer Coefficient ◽  
Trailing Edge ◽  
Power Extraction ◽  
The Impact

The steady improvement of aircraft engine performance has led toward more compact engine cores with increased structural loads. Compact single-stage high-pressure turbines allow high power extraction, operating in the low supersonic range. The shock waves formed at the airfoil trailing edge contribute substantially to turbine losses, mainly due to the shock-boundary layer interactions as well as high-frequency forces on the rotor. We propose to control the vane trailing edge shock interaction with the downstream rotor, using a pulsating vane-trailing-edge-coolant at the rotor passing frequency. A linear cascade of transonic vanes was investigated at different Mach numbers, ranging from subsonic to supersonic regimes (0.8, 1.1) at two engine representative Reynolds numbers (4 × 106 and 6 × 106). The steady and unsteady heat flux was retrieved using thin-film two-layered gauges. The complexity of the tests required the development of an original heat transfer postprocessing approach. In a single test, monitoring the heat flux data and the wall temperature we obtained the adiabatic wall temperature and the convective heat transfer coefficient. The right-running trailing edge shock wave impacts on the neighboring vane suction side. The impact of the shock wave on the boundary layer creates a separation bubble, which is very sensitive to the intensity and angle of the shock wave. Increasing the coolant blowing rate induces the shock to be less oblique, moving the separation bubble upstream. A similar effect is caused by the pulsations of the coolant

Convective heat transfer measured directly with a heat flux sensor

1990 ◽  
Vol 68 (3) ◽  
pp. 1275-1281 ◽  
Author(s):  
U. Danielsson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
The Body ◽  
Heat Flux Sensor ◽  
Calibration Constant

A heat flux disk has been developed that directly measures the convective heat transfer in W/m2. When the sensor is calibrated on an aluminum cylinder, the calibration constant obtained is greatest in still air. As air movement increases, the calibration constant is reduced with increasing convective heat transfer coefficient, 0.5%.W-1.m2.K. The influence of wind on the calibration value is greatly reduced when the sensor is attached to a surface with lower thermal conductivity. The local convective heat transfer coefficient (hc) of the human body was measured. The leg acts in a manner similar to that of a cylinder, with the highest hc value at the front facing the wind and the lowest approximately 90 degrees from the wind, and in the wake a value is obtained that is close to the average hc value of the leg. When hc is measured at several angles and positions all over the body, the results indicate that the body acts approximately as a cylinder with a hc value related to the wind speed as hc = 8.6.v0.6 W.m-2.K-1, where v is velocity.

scholarly journals Unsteady Analysis of Blade and Tip Heat Transfer as Influenced by the Upstream Momentum and Thermal Wakes

2008 ◽  
Author(s):  
Ali A. Ameri ◽  
David L. Rigby ◽  
Erlendur Steinthorsson ◽  
James Heidmann ◽  
John C. Fabian
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbine Blade ◽  
Wall Temperature ◽  
Tip Clearance ◽  
Wall Heat Flux ◽  
Transfer Coefficients ◽  
Adiabatic Wall

The effect of the upstream wake on the blade heat transfer has been numerically examined. The geometry and the flow conditions of the first stage turbine blade of GE’s E3 engine with a tip clearance equal to 2% of the span was utilized. Based on numerical calculations of the vane, a set of wake boundary conditions were approximated which were subsequently imposed upon the downstream blade. This set consisted of the momentum and thermal wakes as well as the variation in modeled turbulence quantities of turbulence intensity and the length scale. Using a one blade periodic domain, the distributions of unsteady heat transfer rate on the turbine blade and its tip, as affected by the wake, were determined. Such heat transfer coefficient distribution was computed using the wall heat flux and the adiabatic wall temperature to desensitize the heat transfer coefficient to the wall temperature. For the determination of the wall heat flux and the adiabatic wall temperatures, two set of computations were required. The results were used in a phase-locked manner to compute the unsteady or steady heat transfer coefficients. It has been found that the unsteady wake has some effect on the distribution of the time averaged heat transfer coefficient on the blade and that this distribution is different from the distribution that is obtainable from a steady computation. This difference was found to be as large as 20 percent of the average heat transfer on the blade surface. On the tip surface, this difference is comparatively smaller and can be as large as four percent of the average.

The Infrared Characteristics of the Wall Temperature of Boiling Heat Transfer in Microchannel

2011 ◽  
Vol 383-390 ◽  
pp. 811-815
Author(s):  
Hu Gen Ma ◽  
Jian Mei Bai ◽  
Rong Jian Xie ◽  
Wen Jing Tu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Wall Temperature ◽  
Boiling Heat Transfer ◽  
Transfer Test ◽  
Axial Direction ◽  
Transfer Model ◽  
Micro Channel ◽  
Vapor Quality ◽  
Test Rig

In this paper, the boiling heat transfer test rig was designed and built, while the characteristics of boiling Heat Transfer of refrigerants in micro-channel was researched. The wall temperature of micro-channel was measured by TH5104 Infrared thermography. The results showed that there were obvious variations for wall temperature of micro-channel along the axial direction when boiling heat transfer occurred in the micro-channel. The temperature distribution affected obviously by the heat flux, mass flow rate; vapor quality and heat transfer model.

Sign in / Sign up

Export Citation Format

Share Document