Numerical modeling of pressure pulsations in the turbo expender of perspective cryostatting system
Aircraft engines and power generators
Аuthors*, **, ***, ****
Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia
Modern cryostatting systems find important applications in power and space transportation systems. The cryostatting system is a closed hydraulic loop for the thermal management and control of thermal modes of superconducting cable lines, cryogenic rocket and space units fuel tanks. The working medium is liquid nitrogen. One of the main components of such a system is the criorefrigirator. In the criorefrigirator compression scheme is used with following expansion of neon in the turboexpander, machine with gas-static bearings. Urgent task in the design phase is to determine the pressure fluctuations in the flow of the turbo expander and dynamic loading of the structure. This paper presents the numerical simulation of unsteady gas-dynamic processes in the turbo expander radial turbine flow. Expansion turbine consists of mounted on the same shaft the radial turbine impeller and centrifugal compressor first stage, that also serves as a gas-dynamic brake. Gas is fed to the expander casing through two pipelines. Further, it is accelerated in the nozzle cascade and enters the turbine impeller blades. After expansion and reduction the temperature, the exhaust gas passes through the axial diffuser. Rotor speed is 25,200 rev / min. The geometry of the computational domain is developed in order to capture the main features of the flow in the working fluid cavity, including the geometry of fourteen working blades and eight vanes of the nozzle cascade. The computational domain is divided into three sub-regions: the casing of the nozzle cascade, rotor, exhaust part. The problem is solved with the use of so-called sliding surfaces which serve for transmitting the data from the rotor, where the calculation is carried out in a rotating coordinate system into the stator zone accounting an angular displacement and sub-grid interpolation. Time step chosen from the condition to ensure the angular displacement in one time step within a single cell of the computational grid. The instantaneous velocity, pressure, temperature and Mach number fields are obtained with calculations. Few points in the nozzle vane channel oblique zones are selected to fix pressure pulsations. The spectral analysis of the data reveal that the tonal component with blades passing frequency dominates the spectra of pressure pulsations, its amplitude is above 7000 Pa. Calculation of loading on nozzle blade gives the amplitude of force 2 N and amplitude of momentum 0.03 N m
Keywords:criorefrigirator, turbo-expender, sliding surface, numerical modelling, pressure pulsation spectra, blade passing frequency
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