The Effects of Wet Compression and Blade Tip Water Injection on the Stability of a Transonic Compressor Rotor

Abstract

The rotor blade tip leakage fiow and associated formation of the tip leakage vortex and interaction of the tip leakage vortex with the shockwave, particularly in the case of a transonic compressor rotor have significant impact on the compressor performance and its stability. Air injection upstream of the compressor rotor tip has been shown to improve compressor performance and enhance its stability. The air required for rotor blade tip injection is generally taken from the later stages of the compressor thus causing penalty on the gas turbine performance. In this study, effects of water injection at the rotor tip with and without the wet compression on the compressor performance and its stability have been examined. To achieve the stated objectives, the well tested transonic compressor rotor stage, NASA rotor stage 37, has been numerically simulated. The evaluation of results on various performance parameters, such as total pressure ratio, inlet fiow capacity, and adiabatic efficiency combined with contours of total pressure losses, entropy. Mach number, and temperature including limiting streamlines, shows that the blade tip water injection could help in reducing low energy region downstream of the Shockwave and strength of the tip leakage vortex with the compressor operating at its rotating stall boundary condition. The extent of reduction depends on the droplet size, injection fiow rate, and its velocity. Furthermore, results show that combined case of the blade tip water injection and the wet compression could provide better stall margin enhancement than the blade tip water injection case.

Influence of wet compression on aerodynamic performance and stability boundary of transonic compressor

“…The comparison of the characteristic curve (pressure ratio and efficiency vs flow rate) under dry compression and different spray wet conditions is shown in Figure 4, where the wet compression efficiency is defined in the same way as Luo. 21 It can be seen that the total pressure ratio of the compressor increases obviously for the small droplet size of 1 μm. Because the small droplets have stronger evaporation and cooling effect, a prominent wet compression effect for improving the compressor pressure ratio can be achieved.…”

“…Sun et al and Zheng et al 19,20 found that wet compression could improve the performance of compressors and gas turbines by reducing the flow loss and increasing the flow capacity of the compressor; meanwhile, the fuel consumption rate and the amount of nitrogen oxides produced was reduced. Luo et al 21 compared the influence of inlet water spray and tip water spray on the compressor stall boundary and found that both of them can broaden the compressor stall boundary. Yang et al 22 numerically investigated the effect of water ingestion on tip clearance flow in compressor rotors when aircraft is flying in a heavy rain.…”

Numerical study on wet compression in a supercritical air centrifugal compressor

“…The isentropic efficiency of wet compression is calculated by where w wi and w w are the isentropic and actual compression work for wet compression, respectively, which are defined as 30,35 where w da and w v are the isentropic compression work of air and water vapour, respectively. f is the vapour to air ratio, ω is the rotating speed, M t is the torque and m is the mass flow.…”

Effects of water ingestion on the tip clearance flow in compressor rotors

“…Based on the models mentioned above and the reference to many wet compression studies, 11,12,24,25 appropriate numerical method can be used to evaluate the effect of water ingestion on the tip clearance flow in compressor rotors. Unless stated otherwise, all of the simulations described below should follow the following settings.…”

“…By comparing the compressor characteristics under different particle sizes conditions, they clarified that the injected water may expand the stable operating range of compressor when the particle size is small enough (in the range of 5–20 µm). Luo and Zheng 24,25 did some numerical simulations on the aerodynamic performance of a transonic compressor under the inlet fogging condition. The simulated results showed that the presence of water would eliminate the tip leakage vortex and increase the mass flow capacity of cascade.…”