Tip Clearance Flows in Turbine Cascades

This article describes the effects of some factors on the tip clearance flow in axial linear turbine cascades. The measurements of the total pressure loss coefficient are made at the cascade outlets by using a five-hole probe at exit Mach numbers of 0.10, 0.14 and 0.19. At each exit Mach number, experiments are performed at the tip clearance heights of 1.0%, 1.5%, 2.0%, 2.5% and 3.0% of the blade height. The effects of the non-uniform tip clearance height of each blade in the pitchwise direction are also studied. The results show that at a given tip clearance height, generally, total pressure loss rises with exit Mach numbers proportionally. At a fixed exit Mach number, the total pressure loss augments nearly proportionally as the tip clearance height increases. The increased tip clearance heights in the tip regions of two adjacent blades are to be blame for the larger clearance loss of the center blade. Compared to the effects of the tip clearance height, the effects of the exit Mach number and the pitchwise variation of the tip clearance height on the cascade total pressure loss are so less significant to be omitted.

Performance Improvement of Single Screw Compressor by Meshing Clearance Adjustment Used in Refrigeration System

The single screw compressor(SSC)is widely used in air compression and refrigeration systems due to its many advantages.The meshing clearance between the screw groove and gate rotor teeth flank has a significant influence on the compressor performance.In this paper,mathematical calculation models describing the internal working process of the SSC are established in order to evaluate the thermal dynamic characteristics of the compressor under varying meshing clearance heights.The refrigerating capacity,volume efficiency and adiabatic efficiency of the SSC are calculated and discussed.Three prototypes,with different meshing clearance heights,were manufactured to study the internal influence mechanisms.The theoretical model was verified using experimental data and the calculation results strongly agreed with the experimental results.Results demonstrate that comparisons of volume efficiency and adiabatic efficiency between the measured and calculated results exhibited deviations of 3.64%-7.98%and 5.92%-9.4%,respectively.Based on the models,analysis under varying meshing clearance heights and working conditions was performed.Taking into account working performance,actual manufacturing conditions and manufacturing cost limitations,a meshing clearance height range from 0.01 mm to 0.08 mm is suggested.This study can provide important theoretical data and experimental support for the design,manufacturing and optimization of single screw compressors.

Numerical Simulation of Active Control on Tip Leakage Flow in Axial Turbine

In an effort to reduce the blade tip clearance leakage in turbine designs, this article aims to numerically investigate the effects of active jet-flow injected from the blade tip platform upon the blade tip clearance flow. A CFD code integrated with dense-correction-based 3D Reynolds-averaged Navier-Stokes equations together with the well-proven Reynolds stress model (RSM) is adopted. The variation of specific heat is taken into consideration. The effects of jet-flow on the tip clearance flow are simulated ...