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.

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.

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.

Investigation of Convective Heat Transfer of Aqueous Nanofluids in Microchannels Integrated With Temperature Nanosensors

2011 ◽  
Author(s):  
Jiwon Yu ◽  
Seok-won Kang ◽  
Saeil Jeon ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Wall Temperature ◽  
Pure Water ◽  
Bulk Temperature ◽  
Inlet Temperature ◽  
Experimental Conditions ◽  
Forced Convective Heat Transfer

Forced convective heat transfer experiments were performed for internal flow of de-ionized water (DIW) and aqueous nanofluids (ANF) in microchannels that were integrated with a calorimeter apparatus and an array of temperature nanosensors. The heat flux and wall temperature distribution was measured for the different test fluids as a function of fluid inlet temperature, wall temperature, heat flux, nanoparticles concentration, nanoparticle materials (composition, nanoparticle size and shape) and flow rates. Anomalous behavior of the nanofluids in convective heat transfer was observed where the heat flux varied as a function of flow rate and bulk temperature. The heat exchanging surfaces were characterized using electron microscopy (SEM, TEM) to monitor the change in surface characteristics both before and after the experiments. Precipitation of nanoparticles on the walls of the microchannels can lead to the formation of “nano-fins” at low concentrations of the nanoparticles while more rampant precipitation at high concentration of the nanoparticles in the nanofluids can lead to scaling (fouling) of the microchannel surfaces leading to degradation of convective heat transfer — compared to that of pure water under the same experimental conditions. Also, competing effects resulting from the decrease in the specific heat capacity as well as anomalous enhancement in the thermal conductivity of aqueous nanofluids can lead to counter-intuitive behavior of these test liquids during forced convective heat transfer.

Study of the Convective Heat Transfer in a Rotating Coolant Channel

1989 ◽  
Vol 111 (1) ◽  
pp. 43-50 ◽  
Author(s):  
J. Guidez
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Test Section ◽  
Suction Side ◽  
Turbine Rotor ◽  
Internal Cavity ◽  
Transfer Coefficients ◽  
Orthogonal Axis ◽  
Friction Forces

An experimental and theoretical study of convective heat transfer in a rotating coolant channel was inspired by the potential application to cooled turbine rotor blades. The flow that circulates into the internal cavity of the blade is subjected to Coriolis and centrifugal forces, in addition to pressure and friction forces. In this study, the channel is a rectangular-sectioned duct that rotates around an orthogonal axis. The experimental rig is composed of a vacuum enclosure, which includes an electric furnace, and the test section, heated by radiative flux. The temperatures of the wall test section are measured with thermocouples and the infrared pyrometer technique still under development. The convective heat transfer coefficients are determined with transient or steady-state techniques. It is shown that Coriolis acceleration has a beneficial influence on mean heat transfer. Locally, along the pressure side, the transfer increases strongly and on the contrary along the suction side, it decreases slightly. These effects are analyzed theoretically with a Navier-Stokes three dimensional (with mixing length model of turbulence) and explained by the influence of Coriolis force, which induces a secondary flow and distorts the velocity and temperature profiles. Experimental and theoretical results are presented and discussed.

Prediction of the Turbine Tip Convective Heat Flux Using Discrete Green's Functions

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Valeria Andreoli ◽  
David G. Cuadrado ◽  
Guillermo Paniagua
Keyword(s):  
Heat Flux ◽  
Convective Heat ◽  
Wall Temperature ◽  
Green's Functions ◽  
Green’S Functions ◽  
Transfer Problem ◽  
Turbine Rotor ◽  
Heat Fluxes ◽  
Viscous Effects ◽  
Adiabatic Wall

The heat fluxes across the turbine tip gap are characterized by large unsteady pressure gradients and shear from the viscous effects. The classical Newton heat convection equation, based on the turbine inlet total temperature, is inadequate. Previous research from our team relied on the use of the adiabatic wall temperature. In this paper, we propose an alternative approach to predict the convective heat transfer problem across the turbine rotor tip using discrete Green's functions (DGF). The linearity of the energy equation in the solid domain with constant thermal properties can be applied with a superposition technique to measure the data extracted from flow simulations to determine the Green's function distribution. The DGF is a matrix of coefficients that relate the temperature spatial (GF) distribution with the heat flux. This methodology is first applied to a backward facing step, validated using experimental data. The final aim of this paper is to demonstrate the method in the rotor turbine tip. A turbine stage at engine-like conditions was assessed using cfd software. The heat flux pulses were applied at different locations in the rotor tip geometry, and the increment of temperature in this zone was evaluated for different clearances, with a consequent variation of the DGF coefficients. Ultimately, a detailed uncertainty analysis of the methodology was included based on the magnitude of the heat flux pulses used in the DGF coefficients calculation and the uncertainty in the experimental measurements of the wall temperature.

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