Optimization of Swirl Brake Design and Assessment of Its Stabilizing Effect on Compressor Rotordynamic Performance
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The rotordynamic stability of high pressure compressors is strongly affected by the aerodynamic effects induced by the gas flow through rotor-stator seals. In particular the tangential velocity (swirl) of the gas flowing through the seals is a main destabilizing factor (Childs, 1993) and therefore needs to be minimized. Swirl brakes are well-known devices to reduce the swirl of the leakage at seal inlet, or preswirl. Their effectiveness is function of several geometrical parameters (swirl brake vane dimensions and shape, clearance gap between rotor and stator, seal diameter) and operating parameters (such as rotating speed, gas pressure, temperature, molecular weight, gas swirl upstream of the seal). A CFD study was carried out in order to evaluate the impact of each geometrical parameter on swirl brake performance, starting from a baseline and varying it over a possible design range. The purpose was to identify an optimum design that could achieve a strong preswirl reduction over the widest range of compressor applications, sizes and operating conditions. Swirl brakes developed according to this optimization study were used in a high pressure centrifugal compressor. The full load test performed in 2013 included a direct measurement of the logarithmic decrement, thus providing useful information to validate the outcome of the analysis. A comparison between calculation and test results allowed to verify the effectiveness of swirl brakes, by quantifying the actual preswirl value obtained from the labyrinth seals.
Baldassarre, Leonardo; Bernocchi, Andrea; Fontana, Michele; Guglielmo, Alberto; Masi, Guido (2014). Optimization of Swirl Brake Design and Assessment of Its Stabilizing Effect on Compressor Rotordynamic Performance. Texas A&M University. Turbomachinery Laboratories. Available electronically from