Measurement and Analysis of Buoyancy-Induced Heat Transfer in Aero-Engine Compressor Rotors

2020 ◽  
Author(s):  
Richard W. Jackson ◽  
Dario Luberti ◽  
Hui Tang ◽  
Oliver J. Pountney ◽  
James A. Scobie ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Outer Region ◽  
Conjugate Problem ◽  
Radial Temperature ◽  
Nusselt Numbers ◽  
Induced Flow ◽  
Aero Engines ◽  
Inner Region ◽  
Buoyancy Induced Flow

Abstract The flow inside cavities between co-rotating compressor discs of aero-engines is driven by buoyancy, with Grashof numbers exceeding 1013. This phenomenon creates a conjugate problem: the Nusselt numbers depend on the radial temperature distribution of the discs, and the disc temperatures depend on the Nusselt numbers. Furthermore, Coriolis forces in the rotating fluid generate cyclonic and anti-cyclonic circulations inside the cavity. Such flows are three-dimensional, unsteady and unstable, and it is a challenge to compute and measure the heat transfer from the discs to the axial throughflow in the compressor. In this paper, Nusselt numbers are experimentally determined from measurements of steady-state temperatures on the surfaces of both discs in a rotating cavity of the Bath Compressor-Cavity Rig. The data are collected over a range of engine-representative parameters and are the first results from a new experimental facility specifically designed to investigate buoyancy-induced flow. The radial distributions of disc temperature were collected under carefully-controlled thermal boundary conditions appropriate for analysis using a Bayesian model combined with the equations for a circular fin. The Owen-Tang buoyancy model has been used to compare predicted radial distributions of disc temperatures and Nusselt numbers with some of the experimentally determined values, taking account of radiation between the interior surfaces of the cavity. The experiments show that the average Nusselt numbers on the disc increase as the buoyancy forces increase. At high rotational speeds the temperature rise in the core, created by compressibility effects in the air, attenuates the heat transfer and there is a critical rotational Reynolds number for which the Nusselt number is a maximum. In the cavity, there is an inner region dominated by forced convection and an outer region dominated by buoyancy-induced flow. The inner region is a mixing region, in which entrained cold throughflow encounters hot flow from the Ekman layers on the discs. Consequently, the Nusselt numbers on the downstream disc in the inner region tend to be higher than those on the upstream disc.

Measurement and Analysis of Buoyancy-Induced Heat Transfer in Aero-Engine Compressor Rotors

2020 ◽  
Author(s):  
Richard Jackson ◽  
Dario Luberti ◽  
Hui Tang ◽  
Oliver J Pountney ◽  
James Scobie ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Conjugate Problem ◽  
Radial Temperature ◽  
Thermal Boundary Conditions ◽  
Nusselt Numbers ◽  
First Results ◽  
Engine Compressor ◽  
Induced Flow ◽  
Aero Engines

Abstract The flow inside cavities between co-rotating compressor discs of aero-engines is driven by buoyancy, with Grashof numbers exceeding 1013. This phenomenon creates a conjugate problem: the Nusselt numbers depend on the radial temperature distribution of the discs, and the disc temperatures depend on the Nusselt numbers. Furthermore, Coriolis forces in the rotating fluid generate cyclonic and anti-cyclonic circulations inside the cavity. Such flows are three-dimensional, unsteady and unstable, and it is a challenge to compute and measure the heat transfer from the discs to the axial throughflow in the compressor. In this paper, Nusselt numbers are experimentally determined from measurements of steady-state temperatures on the surfaces of both discs in a rotating cavity of the Bath Compressor-Cavity Rig. The data are collected over a range of engine-representative parameters and are the first results from a new experimental facility specifically designed to investigate buoyancy-induced flow. The radial distributions of disc temperature were collected under carefully-controlled thermal boundary conditions appropriate for analysis using a Bayesian model combined with the equations for a circular fin. The Owen-Tang buoyancy model has been used to compare predicted radial distributions of disc temperatures and Nusselt numbers with some of the experimentally determined values, taking account of radiation between the interior surfaces of the cavity. The experiments show that the average Nusselt numbers on the disc increase as the buoyancy forces increase. At high rotational speeds the temperature rise in the core, created by compressibility effects in

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

2017 ◽  
Vol 140 (3) ◽  
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 ◽  
Aero Engines ◽  
Buoyancy Induced Flow

The cavities between the rotating compressor disks in aero-engines are open, and there is an axial throughflow of cooling air in the annular space between the center of the disks 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 center of the compressor disks—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 center of compressor disks—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.

Use of Fin Equation to Calculate Nusselt Numbers for Rotating Discs

2015 ◽  
Author(s):  
Hui Tang ◽  
Tony Shardlow ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Conjugate Problem ◽  
Temperature Measurements ◽  
Rotating Disc ◽  
Nusselt Numbers ◽  
Rotating Discs ◽  
Induced Flow ◽  
Buoyancy Induced Flow

Conduction in thin discs can be modelled using the fin equation, and there are analytical solutions of this equation for a circular disc with a constant heat-transfer coefficient. However, convection (particularly free convection) in rotating-disc systems is a conjugate problem: the heat transfer in the fluid and the solid are coupled, and the relative effects of conduction and convection are related to the Biot number, Bi, which in turn is related to the Nusselt number. In principle, if the radial distribution of the disc temperature is known then Bi can be determined numerically. But the determination of heat flux from temperature measurements is an example of an inverse problem where small uncertainties in the temperatures can create large uncertainties in the computed heat flux. In this paper, Bayesian statistics are applied to the inverse solution of the circular fin equation to produce reliable estimates of Bi for rotating discs, and numerical experiments using simulated noisy temperature measurements are used to demonstrate the effectiveness of the Bayesian method. Using published experimental temperature measurements, the method is also applied to the conjugate problem of buoyancy-induced flow in the cavity between corotating compressor discs.

Investigation on the Radial Heat-Transfer of Pumping Secondary Flow in Semiclosed Rotating Disk Cavity

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Guohu Luo ◽  
Zhenqiang Yao
Keyword(s):  
Heat Transfer ◽  
Secondary Flow ◽  
Outer Region ◽  
Rotating Disk ◽  
Mean Flow ◽  
Coolant Pump ◽  
Radial Temperature ◽  
Type Flow ◽  
Radial Heat ◽  
Inner Region

Abstract This study investigates the mean flow and radial heat-transfer behaviors in semiclosed rotating disk cavity within the canned reactor coolant pump. The flow in the semiclosed cavity contains the Stewartson type flow at inner region and the Batchelor type flow at outer region. The heat is radially transported from the outer rim of the semiclosed disk cavity to discharge-hole through the nondirect discharge (ND) portion of the superimposed flow from inlet. The effects of rotating Reynolds numbers, cavity aspect ratio and radial location of discharge-hole on the discharge ratio, pumping mass flow rate, local wall shear stress and radial heat-transfer coefficient are examined in the semiclosed rotating cavity flow, respectively. Based on the radial heat transfer behaviors of pumping secondary flow, an equivalent thermal network is proposed and validated by experiments, which can effectively predict the radial temperature distribution from the discharge hole to periphery with the viscous-heating and nonisothermal effects.

scholarly journals LARGE EDDY SIMULATIONS OF HIGH ROSSBY NUMBER FLOW IN THE HIGH PRESSURE COMPRESSOR INTER-DISK CAVITY

2021 ◽  
pp. 1-22
Author(s):  
Deepak Saini ◽  
Richard Sandberg
Keyword(s):  
Rayleigh Number ◽  
Outer Region ◽  
Large Eddy Simulations ◽  
Rossby Number ◽  
Air Cooling ◽  
Large Eddy ◽  
Number Flow ◽  
Induced Flow ◽  
Inner Region ◽  
Buoyancy Induced Flow

Abstract The focus of the present study is to understand the effect of Rayleigh number on a high Rossby number flow in a high pres- sure compressor (HPC) inter-disk cavity. These cavities form between the compressor disks of a gas turbine engine, and they are an integral part of the internal air cooling system. We perform highly resolved large eddy simulations for two Rayleigh numbers of 0.76 × 108 and 1.54 × 108 at a fixed Rossby number of 4.5 by solving the compressible Navier–Stokes equations. The results show a flow structure dominated by a toroidal vortex in the inner region of the cavity. In the outer region, the flow is observed to move radially outwards by Ekman layers formed on the side disks and to move radially inwards through the central core region of the cavity. An enhancement in the intensity of the radial flares is observed in the outer region of the cavity for the high Rayleigh number case with no perceivable effect in the inner region. The near shroud region is mostly dominated by the centrifugal buoyancy-induced flow and the wall Nusselt number calculated at the shroud is in close agreement with centrifugal buoyancy-induced flow without an axial bore flow.

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.

scholarly journals Buoyancy-Induced Flow and Heat Transfer in Compressor Rotors

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Hui Tang ◽  
Mark R. Puttock-Brown ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Temperature Rise ◽  
Radial Growth ◽  
Radial Clearance ◽  
Rotating Disks ◽  
Compressor Blades ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Induced Flow ◽  
Buoyancy Induced Flow

The buoyancy-induced flow and heat transfer inside the compressor rotors of gas-turbine engines affects the stresses and radial growth of the compressor disks, and it also causes a temperature rise in the axial throughflow of cooling air through the center of the disks. In turn, the radial growth of the disks affects the radial clearance between the rotating compressor blades and the surrounding stationary casing. The calculation of this clearance is extremely important, particularly in aeroengines where the increase in pressure ratios results in a decrease in the size of the blades. In this paper, a published theoretical model—based on buoyancy-induced laminar Ekman-layer flow on the rotating disks—is extended to include laminar free convection from the compressor shroud and forced convection between the bore of the disks and the axial throughflow. The predicted heat transfer from these three surfaces is then used to calculate the temperature rise of the throughflow. The predicted temperatures and Nusselt numbers are compared with measurements made in a multicavity compressor rig, and mainly good agreement is achieved for a range of Rossby, Reynolds, and Grashof numbers representative of those found in aeroengine compressors. Owing to compressibility effects in the fluid core between the disks—and as previously predicted—increasing rotational speed can result in an increase in the core temperature and a consequent decrease in the Nusselt numbers from the disks and shroud.

scholarly journals Large Eddy Simulations of High Rossby Number Flow in the High Pressure Compressor Inter-Disk Cavity

2020 ◽  
Author(s):  
Deepak Saini ◽  
Richard D. Sandberg
Keyword(s):  
Outer Region ◽  
Large Eddy Simulations ◽  
Rossby Number ◽  
High Pressure Compressor ◽  
Large Eddy ◽  
Number Flow ◽  
Induced Flow ◽  
Inner Region ◽  
Buoyancy Induced Flow ◽  
Pressure Compressor

Abstract The focus of the present study is to understand the effect of Rayleigh number on a high Rossby number flow in a high pressure compressor (HPC) inter-disk cavity. These cavities form between the compressor disks of a gas turbine engine, and they are an integral part of the internal air cooling system. We perform highly resolved large eddy simulations for two Rayleigh numbers of 0.76 × 108 and 1.54 × 108 at a fixed Rossby number of 4.5 by solving the compressible Navier–Stokes equations. The results show a flow structure dominated by a toroidal vortex in the inner region of the cavity. In the outer region, the flow is observed to move radially outwards by Ekman layers formed on the side disks and to move radially inwards through the central core region of the cavity. An enhancement in the intensity of the radial flares is observed in the outer region of the cavity for the high Rayleigh number case with no perceivable effect in the inner region. The near shroud region is mostly dominated by the centrifugal buoyancy-induced flow and the wall Nusselt number calculated at the shroud is in close agreement with centrifugal buoyancy-induced flow without an axial bore flow.

Use of Fin Equation to Calculate Nusselt Numbers for Rotating Disks

2015 ◽  
Vol 137 (12) ◽  
Author(s):  
Hui Tang ◽  
Tony Shardlow ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Circular Disk ◽  
Rotating Disk ◽  
Conjugate Problem ◽  
Temperature Measurements ◽  
Rotating Disks ◽  
Nusselt Numbers ◽  
Induced Flow ◽  
Thin Disks

Conduction in thin disks can be modeled using the fin equation, and there are analytical solutions of this equation for a circular disk with a constant heat-transfer coefficient. However, convection (particularly free convection) in rotating-disk systems is a conjugate problem: the heat transfer in the fluid and the solid are coupled, and the relative effects of conduction and convection are related to the Biot number,  Bi, which in turn is related to the Nusselt number. In principle, if the radial distribution of the disk temperature is known then Bi  can be determined numerically. But the determination of heat flux from temperature measurements is an example of an inverse problem where small uncertainties in the temperatures can create large uncertainties in the computed heat flux. In this paper, Bayesian statistics are applied to the inverse solution of the circular fin equation to produce reliable estimates of Bi for rotating disks, and numerical experiments using simulated noisy temperature measurements are used to demonstrate the effectiveness of the Bayesian method. Using published experimental temperature measurements, the method is also applied to the conjugate problem of buoyancy-induced flow in the cavity between corotating compressor disks.

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