Rotating Cavity With Axial Throughflow of Cooling Air: Flow Structure

1992 ◽  
Vol 114 (1) ◽  
pp. 237-246 ◽  
Author(s):  
P. R. Farthing ◽  
C. A. Long ◽  
J. M. Owen ◽  
J. R. Pincombe
Keyword(s):  
Flow Structure ◽  
Vortex Breakdown ◽  
Laser Doppler Anemometry ◽  
Axial Flow ◽  
Angular Speed ◽  
Turbine Engine ◽  
Rotating Cavity ◽  
Wide Range ◽  
Ekman Layers ◽  
Cooling Air

A rotating cavity with an axial throughflow of cooling air is used to provide a simplified model for the flow that occurs between adjacent corotating compressor disks inside a gas turbine engine. Flow visualization and laser-Doppler anemometry are employed to study the flow structure inside isothermal and heated rotating cavities for a wide range of axial-gap ratios, G, rotational Reynolds number, Reφ, axial Reynolds numbers, Rez, and temperature distributions. For the isothermal case, the superposed axial flow of air generates a powerful toroidal vortex inside cavities with large gap ratios (G ≳ 0.400) and weak counterrotating toroidal vortices for cavities with small gap ratios. Depending on the gap ratio and the Rossby number, ε (where ε ∝ Rez/Reφ), axisymmetric and nonaxisymmetric vortex breakdown can occur, but circulation inside the cavity becomes weaker as e is reduced. For the case where one or both disks of the cavity are heated, the flow becomes nonaxisymmetric: Cold air enters the cavity in a “radial arm” on either side of which is a vortex. The cyclonic and anticyclonic circulations inside the two vortices are presumed to create the circumferential pressure gradient necessary for the air to enter the cavity (in the radial arm) and to leave (in Ekman layers on the disks). The core of fluid between the Ekman layers precesses with an angular speed close to that of the disks, and vortex breakdown appears to reduce the relative speed of precession.

Rotating Cavity With Axial Throughflow of Cooling Air: Flow Structure

1990 ◽  
Author(s):  
P. R. Farthing ◽  
C. A. Long ◽  
J. M. Owen ◽  
J. R. Pincombe
Keyword(s):  
Flow Structure ◽  
Vortex Breakdown ◽  
Laser Doppler Anemometry ◽  
Axial Flow ◽  
Reynolds Numbers ◽  
Angular Speed ◽  
Rotating Cavity ◽  
Wide Range ◽  
Ekman Layers ◽  
Cooling Air

A rotating cavity with an axial throughflow of cooling air is used to provide a simplified model for the flow that occurs between adjacent corotating compressor discs inside a gas-turbine engine. Flow visualization and laser-Doppler anemometry are employed to study the flow structure inside isothermal and heated rotating cavities for a wide range of axial-gap ratios. G. rotational. Reynolds numbers, Reφ, axial Reynolds numbers, Rez, and temperature distributions. For the isothermal case, the superposed axial flow of air generates a powerful toroidal vortex inside cavities with large gap ratios (G > 0.400) and weak counter-rotating toroidal vortices for cavities with small gap ratios. Depending on the gap ratio and the Rossby number, ε (where ε ∝ Rez/Reφ), axisymmetric and nonaxisymmetric vortex breakdown can occur, but circulation inside the cavity becomes weaker as ε is reduced. For the case where one or both discs of the cavity are heated, the flow becomes nonaxisymmetric: cold air enters the cavity in a “radial arm” on either side of which is a vortex. The cyclonic and anti-cyclonic circulations inside the two vortices are presumed to create the circumferential pressure gradient necessary for the air to enter the cavity (in the radial arm) and to leave (in Ekman layers on the discs). The core of fluid between the Ekman layers precesses with an angular speed close to that of the discs, and vortex breakdown appears to reduce the relative speed of precession.

Flow and Heat Transfer in a Rotating Cavity With a Stationary Stepped Casing

2000 ◽  
Author(s):  
Abdul A. Jaafar ◽  
Fariborz Motallebi ◽  
Michael Wilson ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Laser Doppler Anemometry ◽  
Tangential Component ◽  
Rotating Disc ◽  
Turbine Engine ◽  
Flow And Heat Transfer ◽  
Rotating Cavity ◽  
Rotating Discs ◽  
Cooling Air

In this paper, new experimental results are presented for the flow in a co-rotating disc system with a rotating inner cylinder and a stationary stepped outer casing. The configuration is based on a turbine disc-cooling system used in a gas turbine engine. One of the rotating discs can be heated, and cooling air is introduced through discrete holes angled inward at the periphery of this disc. The cooling air leaves the system through axial clearances between the discs and the outer casing. Some features of computed flows, and both measured and computed heat transfer, were reported previously for this system. New velocity measurements, obtained using Laser Doppler Anemometry, are compared with results from axisymmetric, steady, turbulent flow computations obtained using a low-Reynolds-number k-ε turbulence model. The measurements and computations show that the tangential component of velocity is invariant with axial location in much of the cavity, and the data suggest that Rankine (combined free and forced) vortex flow occurs. The computations fail to reproduce this behaviour, and there are differences between measured and computed details of secondary flow recirculations. Possible reasons for these discrepancies, and their importance for the prediction of associated heat transfer, are discussed.

Buoyancy-Induced Flow in a Heated Rotating Cavity

2004 ◽  
Vol 128 (1) ◽  
pp. 128-134 ◽  
Author(s):  
J. Michael Owen ◽  
Jonathan Powell
Keyword(s):  
Laser Doppler Anemometry ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Velocity Measurements ◽  
Turbine Engine ◽  
Rotating Cavity ◽  
Heated Disk ◽  
Induced Flow ◽  
Cooling Air ◽  
Buoyancy Induced Flow

Experimental measurements were made in a rotating-cavity rig with an axial throughflow of cooling air at the center of the cavity, simulating the conditions that occur between corotating compressor disks of a gas-turbine engine. One of the disks in the rig was heated, and the other rotating surfaces were quasi-adiabatic; the temperature difference between the heated disk and the cooling air was between 40 and 100°C. Tests were conducted for axial Reynolds numbers, Rez, of the cooling air between 1.4×103 and 5×104, and for rotational Reynolds numbers, Reϕ, between 4×105 and 3.2×106. Velocity measurements inside the rotating cavity were made using laser Doppler anemometry, and temperatures and heat flux measurements on the heated disk were made using thermocouples and fluxmeters. The velocity measurements were consistent with a three-dimensional, unsteady, buoyancy-induced flow in which there was a multicell structure comprising one, two, or three pairs of cyclonic and anticyclonic vortices. The core of fluid between the boundary layers on the disks rotated at a slower speed than the disks, as found by other experimenters. At the smaller values of Rez, the radial distribution and magnitude of the local Nusselt numbers, Nu, were consistent with buoyancy-induced flow. At the larger values of Rez, the distribution of Nu changed, and its magnitude increased, suggesting the dominance of the axial throughflow.

Vortex breakdown in a rotating cylindrical cavity

1979 ◽  
Vol 90 (1) ◽  
pp. 109-127 ◽  
Author(s):  
J. M. Owen ◽  
J. R. Pincombe
Keyword(s):  
Pressure Drop ◽  
Turbulent Flow ◽  
Vortex Breakdown ◽  
Laser Doppler Anemometry ◽  
Axial Flow ◽  
Pressure Measurements ◽  
Rotating Cavity ◽  
Inner Radius ◽  
Laminar And Turbulent Flow ◽  
Velocity Spectra

Flow visualization, laser-Doppler anemometry and pressure measurements have been used to identify and delineate the regimes of vortex breakdown in a rotating cavity with a central axial flow of air. For the particular cavity tested (where the ratio of the outer to the inner radius was ten and the ratio of the axial width to the inner radius was approximately five), spiral breakdown and axisymmetric breakdown occur in both laminar and turbulent flow. Rossby numbers ε characterizing the boundaries between the breakdown modes were established from visual observations of flow behaviour, from discontinuities in velocity components and in the pressure drop across the cavity, and from changes in the velocity spectra. In laminar flow, spiral breakdown occurs for 1·6 [lsim ] ε [lsim ] 3·2 and axisymmetric breakdown occurs for 0·8 [lsim ] ε [lsim ] 1·5. In turbulent flow, spiral breakdown occurs for 21 [lsim ] ε [lsim ] 100 and 1·5 [lsim ] ε [lsim ] 2·6, and axisymmetric breakdown occurs for 2·6 [lsim ] ε [lsim ] 21 and 0·8 [lsim ] ε [lsim ] 1·5. At the higher Rossby numbers, the flow under laminar conditions is significantly different to that under turbulent conditions; at the lower Rossby numbers, it was found to be impossible to distinguish between laminar and turbulent flow.

Rotating Cavity With Axial Throughflow of Cooling Air: Heat Transfer

1992 ◽  
Vol 114 (1) ◽  
pp. 229-236 ◽  
Author(s):  
P. R. Farthing ◽  
C. A. Long ◽  
J. M. Owen ◽  
J. R. Pincombe
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Simple Correlation ◽  
Nusselt Numbers ◽  
Rotating Cavity ◽  
Wide Range ◽  
Effects Of Radiation ◽  
Increasing Temperature ◽  
Cooling Air ◽  
Made In

Heat transfer measurements were made in two rotating cavity rigs, in which cooling air passed axially through the center of the disks, for a wide range of flow rates, rotational speeds, and temperature distributions. For the case of a symmetrically heated cavity (in which both disks have the same temperature distribution), it was found that the distributions of local Nusselt numbers were similar for both disks and the effects of radiation were negligible. For an asymmetrically heated cavity (in which one disk is hotter than the other), the Nusselt numbers on the hotter disk were similar to those in the symmetrically heated cavity but greater in magnitude than those on the colder disks; for this case, radiation from the hot to the cold disk was the same magnitude as the convective heat transfer. Although the two rigs had different gap ratios (G = 0.138 and 0.267), and one rig contained a central drive shaft, there was little difference between the measured Nusselt numbers. For the case of “increasing temperature distribution” (where the temperature of the disks increases radially), the local Nusselt numbers increase radially; for a “decreasing temperature distribution,” the Nusselt numbers decrease radially and become negative at the outer radii. For the increasing temperature case, a simple correlation was obtained between the local Nusselt numbers and the local Grashof numbers and the axial Reynolds number.

Computational Study of the Unsteady Flow Structure of the Buoyancy-Driven Rotating Cavity With Axial Throughflow of Cooling Air

2009 ◽  
Author(s):  
Zain Dweik ◽  
Roger Briley ◽  
Timothy Swafford ◽  
Barry Hunt
Keyword(s):  
Flow Structure ◽  
Rotational Speed ◽  
Operating Conditions ◽  
Structure Evolution ◽  
High Rotational Speed ◽  
Wide Range ◽  
Recirculation Zones ◽  
Cooling Air ◽  
The Impact ◽  
Engine Power

Buoyancy driven flows such as the one that occurs in the inter-disk space of an axial compressor spool plays a major role in determining the gas turbine engine projected life and performance. Details of the developed flow structure inside these spaces largely impact the operating temperatures on the rotating walls of the compressor hardware and therefore impact the life of the machine. In this paper the impact of engine power condition (Idle, Highpower, and Shutdown) on the flow structure for these rotating cavities is studied under a wide range of operating conditions encountered by realistic turbomachines. A computational analysis is performed using commercially available computational tools for grid generation (ICEM-CFD) and turbulent-flow simulation (CFX). A computational test case was developed to imitate the rig-test conditions of Owen and Powell, and computed results were assessed and validated by comparison with their experimental results. A total of fifteen unsteady CFD cases covering a wide range of operating conditions (Rossby Number Ro, Rotational Rayleigh Number Raφ, and axial Reynolds Number Rez) were analyzed. The computed flow results revealed that the flow structure evolution, starting from a steady state solution, is such that radial arms of different number (according to the engine power condition), surrounded by a co-rotating (cyclonic) and counter-rotating (anti-cyclonic) pair of vortices, start to form at different locations. Cold air from the central jet enters the cavity in these arms under the combined action of the centrifugal buoyancy and the Coriolis forces. As time proceeds, the flow structure tends to become virtually invariant with time in a repeatable pattern. The number of radial arms, strength of recirculation zones, and the degree of invasion of the central cooling air toward the shroud are all dependent on the engine power condition. The computations also revealed that at high rotational speed the flow stabilizes, and the unsteady features of the flow structure (cyclonic and anti-cyclonic recirculation zones surrounding the radial arms, radial invasion of the cooling air in the radial arms, and its final impingement upon the shroud surface) eventually disappear after a threshold value of the rotational speed is reached.

Heat Transfer in Rotating Cylindrical Cavities

1977 ◽  
Vol 19 (4) ◽  
pp. 175-187 ◽  
Author(s):  
J. M. Owen ◽  
E. D. Bilimoria
Keyword(s):  
Vortex Breakdown ◽  
Laser Doppler Anemometry ◽  
Flow Rates ◽  
Nusselt Numbers ◽  
Rotating Discs ◽  
Ekman Layers ◽  
Heated Disc ◽  
The Mean ◽  
Cylindrical Cavities ◽  
Radial Outflow

Nusselt numbers are measured on the heated disc of a rotating cylindrical cavity, with either an axial throughflow or a radial outflow of coolant, over a range of gap ratios, 0.13 ≤ G ≤ 0.4, flow rates up to Re z ≈ 1.8 × 105, rotational speeds up to Reø ≈ 2.5 × 106, and Grashof numbers up to Gr ≈ 1.7 times 1012. For the axial throughflow case, dramatic increases in the values of local Nusselt numbers are observed at certain Rossby numbers; these increases are consistent with the vortex breakdown observed on a separate, isothermal, laser Doppler anemometry (L.D.A.) rig For the radial outflow case, the mean Nusselt numbers show three separate régimes which depend on Re z and Reø but are only weakly affected by G. These three régimes have been identified on the L.D.A. rig and are associated with the presence or absence of Ekman layers on the rotating discs.

Investigation of the Unstable Flow Structure in a Rotating Cavity

2006 ◽  
Author(s):  
Dieter Bohn ◽  
Jing Ren ◽  
Christian Tuemmers
Keyword(s):  
Flow Structure ◽  
Coriolis Force ◽  
System Reliability ◽  
Gas Turbines ◽  
Buoyancy Force ◽  
Numerical Results ◽  
Single Pair ◽  
Unstable Flow ◽  
Rotating Cavity ◽  
Cooling Air

Annular cavities are found inside rotor shafts of turbomachines with an axial or radial throughflow of cooling air, which influences the thermal efficiency and system reliability of the gas turbines. The flow and heat transfer phenomena in those cavities should be investigated in order to minimize the thermal load and guarantee system reliability. An experimental rig is set up in the Institute of Steam and Gas Turbines to analyze the flow structure inside the rotating cavity with an axial throughflow of cooling air. The corresponding 3D numerical investigation is carried out with the in-house fluid solver CHTflow, in which the Coriolis force and the buoyancy force are implemented in the time-dependent Navier-Stokes equations. Both the experimental and numerical results show the whole flow structure rotating against the cavity rotating direction. The flow passing the observation windows shows the quite similar trajectories in the experimental and numerical results. The computed sequences and periods of the vortex flow structure correspond closely with those observed in the experiment. Furthermore, the numerical analysis reveals a flow pattern changing between single pair, double pairs and triple pairs vortices. It is suggested that the vortices inside the cavity are created by the gravitational buoyancy force in the investigated case, and the number and strength of the vortices are controlled mainly by the Coriolis force.

Velocity measurements inside a rotating cylindrical cavity with a radial outflow of fluid

1980 ◽  
Vol 99 (1) ◽  
pp. 111-127 ◽  
Author(s):  
J. M. Owen ◽  
J. R. Pincombe
Keyword(s):  
Flow Structure ◽  
Cylindrical Cavity ◽  
Laser Doppler Anemometry ◽  
Reverse Flow ◽  
Radius Ratio ◽  
Velocity Measurements ◽  
Potential Core ◽  
Inner Radius ◽  
Ekman Layers ◽  
Radial Outflow

Flow visualization and laser-doppler anemometry have been used to determine the flow structure and measure the velocity distribution inside a rotating cylindrical cavity with an outer to inner radius ratio of 10, and an axial spacing to inner radius ratio of 2·67. A flow structure comprising an inner layer, Ekman layers, an outer layer and an interior potential core has been confirmed for the cases where the inlet air enters the cavity either axially, through a central hole, or radially, through a central gauze tube, and leaves radially through a series of holes in the peripheral shroud. Velocity measurements in the laminar Ekman layers agree well with the ‘modified linear theory’, and long-and short-wavelength disturbances (which have been reported by other experimenters) have been observed on the Ekman layers when the radial Reynolds number exceeds a critical value. The phenomenon of reverse flow in the Ekman layers and the possibility of ingress of external fluid through the holes in the shroud have also been observed.

Prediction of Heat Transfer in a Rotating Cavity With a Radial Outflow

1991 ◽  
Vol 113 (1) ◽  
pp. 115-122 ◽  
Author(s):  
C. L. Ong ◽  
J. M. Owen
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Boundary Layer Equations ◽  
Nusselt Numbers ◽  
Eddy Viscosity Model ◽  
Rotating Cavity ◽  
Wide Range ◽  
Turbine Disks ◽  
Radial Outflow ◽  
Cooling Air

Solutions of the differential boundary-layer equations, using the Keller-box scheme and the Cebeci-Smith eddy-viscosity model for turbulent flow, have been used to predict the Nusselt numbers on the disks of a heated rotating cavity with a radial outflow of cooling air. Computed Nusselt numbers were in satisfactory agreement with analytical solutions of the elliptic equations for laminar flow and with solutions of the integral equations for turbulent flow. For a wide range of flow rates, rotational speeds, and disk-temperature profiles, the computed Nusselt numbers were in mainly good agreement with measurements obtained from an air-cooled rotating cavity. It is concluded that the boundary-layer equations should provide solutions accurate enough for application to air-cooled gas turbine disks.

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