Rotating Cavity With Axial Throughflow of Cooling Air: Flow Structure

Abstract

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.

How far have we been?

“…The flow structure is found to be significantly influenced by the cavity surface temperature distribution. A quantitative agreement with the experimental flow visualization conducted by Farthing et al [5] is obtained. Long et al [11] have performed numerical simulations of turbulent flows using unsteady Reynolds-averaged NavierStokes and energy equations and a mixing length turbulence model.…”

“…The buoyancy-induced flow structure comprises a parallel array of contra-rotating vortices with horizontal axes. Farthing et al [5] have conducted flow visualization experiments and have shown that the flow patterns in the rotating cavity are functions of the Rossby number and the cavity geometry ratio. It has been found that the whole flow structure moves a little slower than the cavity and against the direction of rotation.…”

Numerical investigation on the flow and heat transfer in a rotor-stator disc cavity

“…Bohn et al [9] performed measurements of the flow and heat transfer in a rotating cavity with axial throughflow. A centrifugal arm and two vortices appeared in their observations, which were similar with that of Farthing et al [10]. Pelle and Harmand [11] experimentally investigated the local heat transfer on the rotor surface in a rotor-stator system with impinging jet.…”

Heat Transfer in High-Pressure Compressor Gas Turbine Internal Air Systems: A Rotating Disc-Cone Cavity With Axial Throughflow

“…In order to establish the fundamental and in uential parameters governing the convective heat transfer, previous work [1][2][3] on this particular con guration has concentrated mostly on an idealized single rotating cavity with an axial through ow of air. Two discs, of outer radius b and inner radius a, are separated by an axial gap s. The rotational speed of the cavity is and the bulk average velocity of the axial through ow is W .…”

“…Laser-illuminated ow visualisation and laser Doppler anemometry (LDA) was used [1] to study the ow structure in unheated (or isothermal) and heated cavities with a b 0.1. The isothermal ow structure was found to be in uenced by the Rossby number, Ro 5 W/ a, and the gap ratio, G 5 s b.…”