Experimental and Numerical Investigation of Tip Leakage Flows in a Roots Blower

Abstract

Computational fluid dynamics (CFD) can help in understanding the nature of leakage flow phenomena inside the rotary positive displacement machines (PDMs). However, due to the lack of experimental results, the analysis of leakage flows in rotary PDMs by CFD has not yet been fully validated. Particle image velocimetry (PIV) tests with a microscopic lens and phase-lock were conducted to obtain the velocity field around the tip gap in an optical Roots blower. The three-dimensional unsteady CFD model of the Roots blower with the dynamic grids generated by Screw Compressor Rotor Grid Generation (SCORG) was established to predict the gap flow under the same operating conditions. The images obtained by the PIV tests were analyzed and some factors which compromise the quality of test results in the gap flow were identified, such as reflections and transparency of the window. The flow fields obtained by CFD have the same flow pattern and velocity magnitude as the experimental results in the majority of observed regions but overestimate the leakage flow velocity. The CFD results show a vortex induced by the leakage flow in the downstream region of the gap. The flow losses in the tip gap mainly happen at the entrance upstream of the gap. Finally, some suggestions for future work are discussed.

Study of leakage flow in oil-free positive displacement rotary machines using particle image velocimetry

“…However, a series of factors deteriorating the results of the PIV test were highlighted, such as limitations in resolving flow features in regions near the gaps and the large sample size required. Numerical analyses of a Roots blower were carried out by Sun et al [14]. It is observed that the CFD flow field agrees with experimental results in the flow pattern and velocity magnitude at certain areas but overestimates the leakage flow velocity.…”

Turbulent flow development within the discharge cavity of a screw compressor

“…The investigations of Stosic 2 and Pascu et al 12 have shown that the use of new techniques for rotors profiling helped to manufacture rotors of complex shapes with tolerances of the order of few microns, which improved efficiencies. Also, a limited number of the previous investigations have been carried out 19,20 to characterise flow leakages using experiments and CFD simulations. The gas pulsations are also a main source of noise within the discharge cavity and have been investigated since 1986 by many authors.…”

The use of laser-induced fluorescence to measure temperature in the leakage gaps of oil-free positive displacement rotary machines

“…An investigation of flow through the male rotor housing clearance of screw machines was carried out by Utri [11] who compared simulation results with flow pictures obtained using the Schlieren method. Recently, an experimental and numerical study of a roots blower in actual running condition was carried out by Sun et al [12], They implemented the PIV technique for clearance flow visualization. A series of factors deteriorating the results of the PIV test were observed such as the surface flaws of the transparent window, the reflection of the surface, the jitter in the phase-locking due to uncertainties in the transmission of the synchronized gear, the accumulation of the liquid particles and the pressure fluctuations.…”