Determination of Separation Losses in the Rotor Wheels of Radial-Axial Turbines
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Journal of Engineering Physics and Thermophysics, Vol. 93, No. 5, September, 2020
DETERMINATION OF SEPARATION LOSSES IN THE ROTOR WHEELS OF RADIAL-AXIAL TURBINES Yu. A. Grishina and V. N. Bakulinb
UDC 629.7.036:629.438
The use of the basic hydrodynamics equations written for the portion of contracted flow at the inlet into the vane channel of the rotor wheel of the radial-axial turbines at considerable angles of attack and for the portion of subsequent expansion up to the reattachment of flow to the channel walls made it possible to obtain analytical dependences (characteristics) of losses on the angles of flow inlet into the channel. The circulation at the inlet into the channel exerts a noticeable influence on the actual angle of the flow that entered into the channel. The obtained method of calculation of losses also makes it possible to take into account the thickness of the blades, on which the region of insensitivity to the angle of attack depends, and to determine the corresponding angles of the flow entry that bound this region. The characteristics of the rotor wheels of radial-axial turbines obtained with the use of the developed method agree well with the known experimental data in a wide range of the angles of attack of flow. Keywords: radial-axial turbine, rotor wheel, angle of attack, circulation, separation losses, characteristics. In solving practical problems and in computational investigations of flow in turbomachines operating in a wide range of regimes, the estimation of profile losses of separation flow occurring at the inlet to the blade assemblies of rotor wheels under off-design conditions of flow is of great value [1–10]. This problem is most essential for numerical simulation of nonstationary gas exchange in piston engines with turbo-supercharging [11–14] where the output pulses ahead of the turbines may have a considerable amplitude. For supercharging the engines intended for the transport, turbo-superchargers (TSCh) with radial-axial turbines (RAT) are used. Fluctuations in the rate and velocity of flow passing through a radial-axial turbine actually exclude the regime of calculated flow past the rotor wheel blades. The vector of the relative velocity at the inlet to the wheel all the time undergoes a change by the absolute value and direction. Positive and negative angles of attack are formed which may attain considerable values, which leads to the origination of separation zones and large losses of the separating flow. At the present time, there are no reliable methods for calculating these losses needed for computational investigations and for development and adaptation of turbo-superchargers for application in engines with turbo-supercharging. It is known that in the vane channels of the rotor wheels of radial turbomachines, of both rotating compressors and turbines, there is intense circulation flow which is imposed on the main flow and leads to a change in the direction of relative velocity. Therefore the most important feature to be taken into account in considering the flow in
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