Fluid Friction and Leakage between a Stationary and Rotating Disc

Abstract

This paper describes an investigation of the flow in a narrow gap between a rotating and stationary disc with an arbitrarily imposed radial pressure difference. This system represents the conditions pertaining between the rotors and casings of many fluid machines.The investigation is mainly experimental, for although the equations of motion were derived for the fluid system in question, these were found not to be tractable for the conditions observed. Experimental results are reported from two separate test series. The first test series yielded data on the frictional and pressure forces in the system which were obtained in sufficient detail for use in design calculations for fluid machinery. In the second series the flow between the discs was studied in detail in order to explain the nature and form of the results obtained in the first series of tests.

Developments in turbomachinery internal air systems

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ABSTRACTBayley and Conway's 1964 paper [1], motivated by shortcomings in industrial design methods and understanding, was one of the first investigations of flow and heat transfer in turbomachinery rotating disc cavities. At the time of the study, a theoretical or numerical treatment was considered intractable and so experiments were undertaken.

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Air Temperature Rises in Compressor and Turbine Stator Wells

“…If fluid is drawn inward to the space between a rotating and a stationary disc at a sufficiently large rate, as by an imposed large pressure drop, between the periphery and axis of the system, the outflow otherwise generated by the rotating member as described above will be completely suppressed. This effect was observed experimentally and related to a simplified criterion by Bayley and Conway (1964). They showed theoretically that there could be no radially outward egress of air when Cw/G.Re, exceeded 27r, Cw in this situation being the dimensionless rate of radially inward flow.…”

“…The moment coefficient can then be assumed to rise with the 0.3 power of the circulation rate through the cavity, as observed by Bayley and Conway (1964). It will have reached the free disc level, certainly by the time the circulation has increased to G,Re0 after which the shear will continue to increase.…”

“…Considering first the simplest situation of a disc rotating in an infinite atmosphere, at speeds high enough for the boundary layers to be turbulent. It can be assumed that the velocity at a distance y from the surface, vy , varies according to a simple power law like vy/vo = (y/5) l/n (1) in which v o is the velocity outside the boundary layer of thickness 6 and n is typically 7. By solution of the integral boundary layer momentum equations with this assumption (Owen and Rogers (1991)), it can be shown that the mass flow, m, in the boundary layer at a radius r, for a Reynolds number, Re4, = wro/v, is given by the dimensionless form Cw = m/j ur = 0 •22[(r/ro ) 2 Re4] 0.8 (2) Similarly for a stator well represented as an annulus extending between inner radius ri and outer, r o , the same approach would give the entrainment outflow in the well, Cw,,,, as a proportion of the entrainment, Cwo , of a free disc of the same outer radius, r o , as…”

“…For the latter case, most data are concerned with either no imposed radial flow between the discs or a radial outflow, and none seems to have considered geometries approximating to the radius ratios typical of stator wells. Further, the effect of a net radial inflow has not often been widely investigated: The research reported by Bayley and Conway (1964) dealt with a superimposed radial inflow of fluid, but accurate measurements of friction torque were only possible in this programme when egress of fluid from the rotor-stator space had been suppressed, as in the `large inflow' regime considered in Section 2.2 above. The investigation showed clearly how raising the rate of radial inflow increased the windage dissipated in the system, which was observed to increase as about the 0.3 power of the rate of inflow.…”