Flow and Heat Transfer in a Preswirl Rotor–Stator System

1997 ◽  
Vol 119 (2) ◽  
pp. 364-373 ◽  
Author(s):  
M. Wilson ◽  
R. Pilbrow ◽  
J. M. Owen
Keyword(s):  
Heat Transfer ◽  
Gas Turbines ◽  
Heat Fluxes ◽  
Valuable Insight ◽  
Swirl Ratio ◽  
Blade Cooling ◽  
Nusselt Numbers ◽  
Air Temperatures ◽  
Via Holes ◽  
Cooling Air

Conditions in the internal-air system of a high-pressure turbine stage are modeled using a rig comprising an outer preswirl chamber separated by a seal from an inner rotor-stator system. Preswirl nozzles in the stator supply the “blade-cooling” air, which leaves the system via holes in the rotor, and disk-cooling air enters at the center of the system and leaves through clearances in the peripheral seals. The experimental rig is instrumented with thermocouples, fluxmeters, pitot tubes, and pressure taps, enabling temperatures, heat fluxes, velocities, and pressures to be measured at a number of radial locations. For rotational Reynolds numbers of Reφ ≃ 1.2 × 106, the swirl ratio and the ratios of disk-cooling and blade-cooling flow rates are chosen to be representative of those found inside gas turbines. Measured radial distributions of velocity, temperature, and Nusselt number are compared with computations obtained from an axisymmetric elliptic solver, featuring a low-Reynolds-number k–ε turbulence model. For the inner rotor-stator system, the computed core temperatures and velocities are in good agreement with measured values, but the Nusselt numbers are underpredicted. For the outer preswirl chamber, it was possible to make comparisons between the measured and computed values for cooling-air temperatures but not for the Nusselt numbers. As expected, the temperature of the blade-cooling air decreases as the inlet swirl ratio increases, but the computed air temperatures are significantly lower than the measured ones. Overall, the results give valuable insight into some of the heat transfer characteristics of this complex system.

scholarly journals Flow and Heat Transfer in a Pre-Swirl Rotor-Stator System

1995 ◽  
Author(s):  
Michael Wilson ◽  
Robert Pilbrow ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Gas Turbines ◽  
Heat Fluxes ◽  
Valuable Insight ◽  
Swirl Ratio ◽  
Blade Cooling ◽  
Nusselt Numbers ◽  
Swirl Chamber ◽  
Air Temperatures ◽  
Cooling Air

Conditions in the internal-air system of a high-pressure turbine stage are modelled using a rig comprising an outer pre-swirl chamber separated by a seal from an inner rotor-stator system. Pre-swirl nozzles in the stator supply the “blade-cooling” air, which leaves the system via holes in the rotor, and disc-cooling air enters at the centre of the system and leaves through clearances in the peripheral seals. The experimental rig is instrumented with thermocouples, fluxmeters, pitot tubes and pressure taps enabling temperatures, heat fluxes, velocities and pressures to be measured at a number of radial locations. For rotational Reynolds numbers of Reϕ ≃ 1.2 × 106, the swirl ratio and the ratios of disc-cooling and blade-cooling flow rates are chosen to be representative of those found inside gas turbines. Measured radial distributions of velocity, temperature and Nusselt number are compared with computations obtained from an axisymmetric elliptic solver, featuring a low-Reynolds-number k-ε turbulence model. For the inner rotor-stator system, the computed core temperatures and velocities are in good agreement with measured values, but the Nusselt numbers are underpredicted. For the outer pre-swirl chamber, it was possible to make comparisons between the measured and computed values for cooling-air temperatures but not for the Nusselt numbers. As expected, the temperature of the blade-cooling air decreases as the swirl ratio increases, but the computed air temperatures are significantly lower than the measured ones. Overall, the results give valuable insight into some of the heat transfer characteristics of this complex system.

Heat Transfer in a “Cover-Plate” Pre-Swirl Rotating-Disc System

1998 ◽  
Author(s):  
Robert Pilbrow ◽  
Hasan Karabay ◽  
Michael Wilson ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Cover Plate ◽  
Swirl Ratio ◽  
Rotating Disc ◽  
Blade Cooling ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Turbine Disc ◽  
Cooling Air

In most gas turbines, blade-cooling air is supplied from stationary pre-swirl nozzles that swirl the air in the direction of rotation of the turbine disc. In the “cover-plate” system, the pre-swirl nozzles are located radially inward of the blade-cooling holes in the disc, and the swirling air flows radially outwards in the cavity between the disc and a cover-plate attached to it. In this combined computational and experimental paper, an axisymmetric elliptic solver, incorporating the Launder-Sharma and the Morse low-Reynolds-number k-ε turbulence models, is used to compute the flow and heat transfer. The computed Nusselt numbers for the heated “turbine disc” are compared with measured values obtained from a rotating-disc rig. Comparisons are presented, for a wide range of coolant flow rates, for rotational Reynolds numbers in the range 0.5 × 106 to 1.5 × 106, and for 0.9 < βp < 3.1, where βp is the pre-swirl ratio (or ratio of the tangential component of velocity of the cooling air at inlet to the system to that of the disc). Agreement between the computed and measured Nusselt numbers is reasonably good, particularly at the larger Reynolds numbers. A simplified numerical simulation is also conducted to show the effect of the swirl ratio and the other flow parameters on the flow and heat transfer in the cover-plate system.

Heat Transfer in a “Cover-Plate” Preswirl Rotating-Disk System

1999 ◽  
Vol 121 (2) ◽  
pp. 249-256 ◽  
Author(s):  
R. Pilbrow ◽  
H. Karabay ◽  
M. Wilson ◽  
J. M. Owen
Keyword(s):  
Heat Transfer ◽  
Rotating Disk ◽  
Reynolds Numbers ◽  
Turbine Disk ◽  
Cover Plate ◽  
Blade Cooling ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Cooling Air ◽  
Plate System

In most gas turbines, blade-cooling air is supplied from stationary preswirl nozzles that swirl the air in the direction of rotation of the turbine disk. In the “cover-plate” system, the preswirl nozzles are located radially inward of the blade-cooling holes in the disk, and the swirling airflows radially outward in the cavity between the disk and a cover-plate attached to it. In this combined computational and experimental paper, an axisymmetric elliptic solver, incorporating the Launder–Sharma and the Morse low-Reynolds-number k–ε turbulence models, is used to compute the flow and heat transfer. The computed Nusselt numbers for the heated “turbine disk” are compared with measured values obtained from a rotating-disk rig. Comparisons are presented, for a wide range of coolant flow rates, for rotational Reynolds numbers in the range 0.5 X 106 to 1.5 X 106, and for 0.9 < βp < 3.1, where βp is the preswirl ratio (or ratio of the tangential component of velocity of the cooling air at inlet to the system to that of the disk). Agreement between the computed and measured Nusselt numbers is reasonably good, particularly at the larger Reynolds numbers. A simplified numerical simulation is also conducted to show the effect of the swirl ratio and the other flow parameters on the flow and heat transfer in the cover-plate system.

scholarly journals Performance of Pre-Swirl Rotating-Disc Systems

1999 ◽  
Author(s):  
Hasan Karabay ◽  
Robert Pilbrow ◽  
Michael Wilson ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Tangential Velocity ◽  
Turbulence Models ◽  
Cover Plate ◽  
Swirl Ratio ◽  
Rotating Disc ◽  
Blade Cooling ◽  
Cooling Air

This paper summarises and extends recent theoretical, computational and experimental research into the fluid mechanics, thermodynamics and heat transfer characteristics of the so-called cover-plate pre-swirl system. Experiments were carried out in a purpose-built rotating-disc rig, and the Reynolds-averaged Navier-Stokes equations were solved using 2D (axisymmetric) and 3D computational codes, both of which incorporated low-Reynolds-number k-ε turbulence models. The free-vortex flow, which occurs inside the rotating cavity between the disc and cover-plate, is controlled principally by the pre-swirl ratio, βp: this is the ratio of the tangential velocity of the air leaving the nozzles to that of the rotating disc. Computed values of the tangential velocity are in good agreement with measurements, and computed distributions of pressure are in close agreement with those predicted by a one-dimensional theoretical model. It is shown theoretically and computationally that there is a critical pre-swirl ratio, βp,crit, for which the frictional moment on the rotating discs is zero, and there is an optimal pre-swirl ratio, βp,opt, where the average Nusselt number is a minimum. Computations show that, for βp < βp,opt, the temperature of the blade-cooling air decreases as βp increases; for βp > βp,opt, whether the temperature of the cooling air increases or decreases as βp increases depends on the flow conditions and on the temperature difference between the disc and the air. Owing to the three-dimensional flow and heat transfer near the blade-cooling holes, and to unquantifiable uncertainties in the experimental measurements, there were significant differences between the computed and measured temperatures of the blade-cooling air. In the main, the 3D computations produced smaller differences than the 2D computations.

The Effect of Disk Geometry on Heat Transfer in a Rotating Cavity With a Radial Outflow of Fluid

1988 ◽  
Vol 110 (1) ◽  
pp. 70-77 ◽  
Author(s):  
P. R. Farthing ◽  
J. M. Owen
Keyword(s):  
Heat Transfer ◽  
Flow Visualization ◽  
Source Region ◽  
Integral Boundary ◽  
Boundary Layer Equations ◽  
Nusselt Numbers ◽  
Via Holes ◽  
Turbine Disks ◽  
Radial Outflow ◽  
Cooling Air

Flow visualization and heat transfer measurements have been made in a cavity comprising two nonplane disks of 762 mm diameter and a peripheral shroud, all of which could be rotated up to 2000 rpm. “Cobs,” made from a lightweight foam material and shaped to model the geometry of turbine disks, were attached to the center of each disk. Cooling air at flow rates up to 0.1 kg/s entered the cavity through the center of the “upstream” disk and left via holes in the shroud. The flow structure was found to be similar to that observed in earlier tests for the plane-disk case: a source region, Ekman layers, sink layer, and interior core were observed by flow visualization. Providing the source region did not fill the entire cavity, solutions of the turbulent integral boundary-layer equations provided a reasonable approximation to the Nusselt numbers measured on the heated “downstream” disk.

Theoretical Model of Buoyancy-Induced Heat Transfer in Closed Compressor Rotors

2017 ◽  
Author(s):  
Hui Tang ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Gas Turbines ◽  
Gravitational Acceleration ◽  
Centripetal Acceleration ◽  
Closed Cavity ◽  
Nusselt Numbers ◽  
Industrial Gas Turbines ◽  
Induced Flow ◽  
Cooling Air ◽  
Buoyancy Induced Flow

The cavities between the rotating compressor discs in aeroengines are open, and there is an axial throughflow of cooling air in the annular space between the centre of the discs and the central rotating compressor shaft. Buoyancy-induced flow occurs inside these open rotating cavities, with an exchange of heat and momentum between the axial throughflow and the air inside the cavity. However, even where there is no opening at the centre of the compressor discs — as is the case in some industrial gas turbines — buoyancy-induced flow can still occur inside the closed rotating cavities. The closed cavity also provides a limiting case for an open cavity when the axial clearance between the cobs — the bulbous hubs at the centre of compressor discs — is reduced to zero. Bohn and his co-workers at the University of Aachen have studied three different closed-cavity geometries, and they have published experimental data for the case where the outer cylindrical surface is heated and the inner surface is cooled. In this paper, a buoyancy model is developed in which it is assumed that the heat transfer from the cylindrical surfaces is analogous to laminar free convection from horizontal plates, with the gravitational acceleration replaced by the centripetal acceleration. The resulting equations, which have been solved analytically, show how the Nusselt numbers depend on both the geometry of the cavity and its rotational speed. The theoretical solutions show that compressibility effects in the core attenuate the Nusselt numbers, and there is a critical Reynolds number at which the Nusselt number will be a maximum. For the three cavities tested, the predicted Nusselt numbers are in generally good agreement with the measured values of Bohn et al. over a large range of Raleigh numbers up to values approaching 1012. The fact that the flow remains laminar even at these high Rayleigh numbers is attributed to the Coriolis accelerations suppressing turbulence in the cavity, which is consistent with recently-published results for open rotating cavities.

Analysis of Shroud and Disc Heat Transfer in Aero-Engine Compressor Rotors

2021 ◽  
Author(s):  
Richard Jackson ◽  
Hui Tang ◽  
James Scobie ◽  
Oliver J Pountney ◽  
Carl Sangan ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Outer Part ◽  
Axial Flow ◽  
Likelihood Estimation ◽  
Heat Fluxes ◽  
Grashof Number ◽  
Nusselt Numbers ◽  
Flux Measurements ◽  
Engine Compressor ◽  
Cooling Air

Abstract Heat transfer within the rotating compressor cavity of an aero_engine is predominantly governed by buoyancy, which can be characterised by the Grashof number. Unsteady and unstable buoyancy_induced flow structures influence the temperatures and stresses in the compressor rotors, and these affect the radial growth of the discs. In addition, the heat transfer from the discs and shroud increases the temperature of the throughflow of cooling air. This paper contains two connected parts. First, a heat transfer correlation for the shroud of a rotating cavity was determined from steady_state heat flux measurements collected in the Bath Compressor_Cavity Rig at engine_simulated conditions. The Nusselt numbers were based on the cavity air temperature adjacent to the shroud, which was predicted using the Owen_Tang buoyancy model. Heat transfer from the shroud was consistent with free convection from a horizontal plate in a gravitational field. Maximum likelihood estimation was used with a Rayleigh_Benard equation to correlate the shroud Nusselt number with the local Grashof number. Secondly, an energy balance was used to calculate the enthalpy rise of the axial throughflow from the measured disc and shroud heat fluxes. Disc fluxes were derived from radial distributions of measured steady_state disc temperatures using a Bayesian model and the equations for a circular fin. The calculated throughflow temperature rise was consistent with direct thermocouple measurements. The complex, three_dimensional flow near the cavity entrance can result in enthalpy exchange penetrating upstream in the throughflow, and rotationally_induced flow can create upstream axial flow in the outer part of the annulus.

Performance of Pre-Swirl Rotating-Disc Systems

2000 ◽  
Vol 122 (3) ◽  
pp. 442-450 ◽  
Author(s):  
Hasan Karabay ◽  
Robert Pilbrow ◽  
Michael Wilson ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Tangential Velocity ◽  
Cover Plate ◽  
Two Dimensional ◽  
Swirl Ratio ◽  
Rotating Disc ◽  
Blade Cooling ◽  
Cooling Air

This paper summarizes and extends recent theoretical, computational, and experimental research into the fluid mechanics, thermodynamics, and heat transfer characteristics of the so-called cover-plate pre-swirl system. Experiments were carried out in a purpose-built rotating-disc rig, and the Reynolds-averaged Navier-Stokes equations were solved using two-dimensional (axisymmetric) and three-dimensional computational codes, both of which incorporated low-Reynolds-number k-ε turbulence models. The free-vortex flow, which occurs inside the rotating cavity between the disc and cover-plate, is controlled principally by the pre-swirl ratio, βp: this is the ratio of the tangential velocity of the air leaving the nozzles to that of the rotating disc. Computed values of the tangential velocity are in good agreement with measurements, and computed distributions of pressure are in close agreement with those predicted by a one-dimensional theoretical model. It is shown theoretically and computationally that there is a critical pre-swirl ratio, βp,crit, for which the frictional moment on the rotating discs is zero, and there is an optimal pre-swirl ratio, βp,opt, where the average Nusselt number is a minimum. Computations show that, for βp<βp,opt, the temperature of the blade-cooling air decreases as βp increases; for βp>βp,opt, whether the temperature of the cooling air increases or decreases as βp increases depends on the flow conditions and on the temperature difference between the disc and the air. Owing to the three-dimensional flow and heat transfer near the blade-cooling holes, and to unquantifiable uncertainties in the experimental measurements, there were significant differences between the computed and measured temperatures of the blade-cooling air. In the main, the three-dimensional computations produced smaller differences than the two-dimensional computations. [S0742-4795(00)01902-5]

A Numerical Study on Conjugate Heat Transfer for Supercritical CO2 Turbine Blade With Cooling Channels

2020 ◽  
Author(s):  
Akshay Khadse ◽  
Andres Curbelo ◽  
Ladislav Vesely ◽  
Jayanta S. Kapat
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Gas Turbines ◽  
Supercritical Co2 ◽  
Conjugate Heat Transfer ◽  
Maximum Temperature ◽  
Inlet Temperature ◽  
Cooling Channels ◽  
Blade Cooling ◽  
Turbine Inlet

Abstract The first stage of turbine in a Brayton cycle faces the maximum temperature in the cycle. This maximum temperature may exceed creep temperature limit or even melting temperature of the blade material. Therefore, it becomes an absolute necessity to implement blade cooling to prevent them from structural damage. Turbine inlet temperatures for oxy-combustion supercritical CO2 (sCO2) are promised to reach blade material limit in near future foreseeing need of turbine blade cooling. Properties of sCO2 and the cycle parameters can make Reynolds number external to blade and external heat transfer coefficient to be significantly higher than those typically experience in regular gas turbines. This necessitates evaluation and rethinking of the internal cooling techniques to be adopted. The purpose of this paper is to investigate conjugate heat transfer effects within a first stage vane cascade of a sCO2 turbine. This study can help understand cooling requirements which include mass flow rate of leakage coolant sCO2 and geometry of cooling channels. Estimations can also be made if the cooling channels alone are enough for blade cooling or there is need for more cooling techniques such as film cooling, impingement cooling and trailing edge cooling. The conjugate heat transfer and aerodynamic analysis of a turbine cascade is carried out using STAR CCM+. The turbine inlet temperature of 1350K and 1775 K is considered for the study considering future potential needs. Thermo-physical properties of this mixture are given as input to the code in form of tables using REFPROP database. The blade material considered is Inconel 718.

Time-Resolved Heat Transfer and Surface Pressure Measurements for a Fully Cooled Transonic Turbine Stage

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Jeremy B. Nickol ◽  
Randall M. Mathison ◽  
Malak F. Malak ◽  
Rajiv Rana ◽  
Jong S. Liu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Field ◽  
Surface Pressure ◽  
High Frequency ◽  
Gas Turbines ◽  
Pressure Measurements ◽  
Turbine Stage ◽  
Cooling Flow ◽  
Blade Cooling

The flow field in axial gas turbines is driven by strong unsteady interactions between stationary and moving components. While time-averaged measurements can highlight many important flow features, developing a deeper understanding of the complicated flows present in high-speed turbomachinery requires time-accurate measurements that capture this unsteady behavior. Toward this end, time-accurate measurements are presented for a fully cooled transonic high-pressure turbine stage operating at design-corrected conditions. The turbine is run in a short-duration blowdown facility with uniform, radial, and hot streak vane-inlet temperature profiles as well as various amounts of cooling flow. High-frequency response surface pressure and heat-flux instrumentation installed in the rotating blade row, stator vane row, and stationary outer shroud provide detailed measurements of the flow behavior for this stage. Previous papers have reported the time-averaged results from this experiment, but this paper focuses on the strong unsteady phenomena that are observed. Heat-flux measurements from double-sided heat-flux gauges (HFGs) cover three spanwise locations on the blade pressure and suction surfaces. In addition, there are two instrumented blades with the cooling holes blocked to isolate the effect of just blade cooling. The stage can be run with the vane and blade cooling flow either on or off. High-frequency pressure measurements provide a picture of the unsteady aerodynamics on the vane and blade airfoil surfaces, as well as inside the serpentine coolant supply passages of the blade. A time-accurate computational fluid dynamics (CFD) simulation is also run to predict the blade surface pressure and heat-flux, and comparisons between prediction and measurement are given. It is found that unsteady variations in heat-flux and pressure are stronger at low to midspan and weaker at high span, likely due to the impact of secondary flows such as the tip leakage flow. Away from the tip, it is seen that the unsteady fluctuations in pressure and heat-flux are mostly in phase with each other on the suction side, but there is some deviation on the pressure side. The flow field is ultimately shown to be highly three-dimensional, as the movement of high heat transfer regions can be traced in both the chord and spanwise directions. These measurements provide a unique picture of the unsteady flow physics of a rotating turbine, and efforts to better understand and model these time-varying flows have the potential to change the way we think about even the time-averaged flow characteristics.

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