Abstract
Abstract Reaction is the fundamental parameter by which the asymmetry of the velocity triangle of a stage is set. Little is understood about the effect that a reaction has on either the efficiency or the operating range of a compressor. A particular difficulty in understanding the effect of the reaction is that the rotor and stator have a natural asymmetry caused by the centrifugal effects in the rotor boundary layer being much larger than that in the stator boundary layer. In this paper, a novel approach has been taken: McKenzie’s “linear repeating stage” concept is used to remove the centrifugal effects. The centrifugal effects are then reintroduced as a body force. This allows the velocity triangle effect and centrifugal force effect to be decoupled. The paper shows the surprising result that, depending on how the solidity is set, a 50% reaction stage can either result in the maximum, or the minimum, profile loss. When the centrifugal effects are removed, 50% reaction is shown to minimize endwall loss, maximize stage efficiency, and maximize operating range. When the centrifugal effects are reintroduced, the compressor with the maximum design efficiency is found to rise in the reaction by 5% (from 50% reaction to 55% reaction) and the compressor with the maximum operating range is found to rise in the reaction by 15% (from 50% reaction to 65% reaction).
Highlights
1.1 Effect of reactionIn the central stages of a multistage compressor, it is typically argued that symmetrical rotor and stator velocity triangles maximise the stage efficiency. Horlock (1958) and Cumpsty (1989) say this is because the static-pressure rise is split between the rotor and stator and so the adverse pressure gradient is balanced
When the centrifugal effects are reintroduced, the compressor with the maximum design efficiency is found to rise in reaction by 5% and the compressor with the maximum operating range is found to rise in reaction by 15%
7.1.2 High reaction compressor Case B represents a second historic design philosophy where the reaction is maintained at 75% through all stages. This benefits from having no Inlet Guide Vane (IGV) or Outlet Guide Vane (OGV), it suffers from having a reaction which has a higher design loss
Summary
In the central stages of a multistage compressor, it is typically argued that symmetrical rotor and stator velocity triangles maximise the stage efficiency. Horlock (1958) and Cumpsty (1989) say this is because the static-pressure rise is split between the rotor and stator and so the adverse pressure gradient is balanced. Horlock (1958) and Cumpsty (1989) say this is because the static-pressure rise is split between the rotor and stator and so the adverse pressure gradient is balanced. In the central stages of a multistage compressor, it is typically argued that symmetrical rotor and stator velocity triangles maximise the stage efficiency. This is the definition of 50% reaction, as described by equation 1.1. Denton (1993) argues for symmetrical velocity triangles maximising the stage efficiency, based on balancing the relative inlet velocities into the rotor and stator. There is a reduction in stage efficiency for asymmetric velocity triangles
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