Tip clearance

About: Tip clearance is a research topic. Over the lifetime, 2637 publications have been published within this topic receiving 32671 citations.

A new endwall model for axial compressor throughflow calculations

Abstract: It is well recognized that the endwall regions of a compressor--in which the annulus wall flow interacts with the mainstream flow--have a major influence on its efficiency and surge margin. Despite many attempts over the years to predict the very complex flow patterns in the endwall regions, current compressor design methods still rely largely on empirical estimates of the aerodynamic losses and flow angle deviations in these regions. This paper describes a new phenomenological model of the key endwall flow phenomena treated in a circumferentially averaged way. It starts from Hirsch and de Ruyck`s annulus wall boundary layer approach, but makes some important changes. The secondary vorticities arising from passage secondary flows and from tip clearance flows are calculated. Then the radial interchanges of momentum, energy, and entropy arising from both diffusion and convection are estimated. The model is incorporated into a streamline curvature program. The empirical blade force defect terms in the boundary layers are selected from cascade data. The effectiveness of the method is illustrated by comparing the predictions with experimental results on both low-speed and high-speed multistage compressors. It is found that the radial variation of flow parameters is quite well predicted, and so is the overallmore » performance, except when significant endwall stall occurs.« less

The effect of injector size on compressor performance in a transonic axial compressor with discrete tip injection

Abstract: The present study investigates the effects of injector size, which covers both circumferential extent and radial extent on compressor stability and radial work redistribution using time-accurate three-dimensional numerical simulations for multi-passages in a transonic compressor with discrete tip injection. Injector width ranges from 1% to 14.5% of casing perimeter and injector throat height varies from 2 to 6 times the height of rotor tip clearance. Six identical injectors are uniformly mounted around the annulus. Results indicate that, with sufficient covering of injection, tip injection can significantly improve compressor stability. Stability margin is improved by 3.5% employing 0.65% of the annulus mass flow. With injector width increased, stability improves sharply when the width is less than 4.5% of casing perimeter, but increases flatly for the rest coverage. Expanding injector throat height to an intermediate level can further enhance compressor stability, but excessive throat height is detriment...

Effects of 3D Aerofoil Tip Clearance Variation on a 4-Stage Low Speed Compressor

Abstract: The aerodynamic performance of turbomachinery airfoils and therefore the overall efficiency of an engine are strongly dependent on the design of the near end wall sections of blades and vanes. In addition, good compressor stability can only be achieved if the running clearance is as small as allowed for save operation. In the engine the radial gap varies in size due to thermal effects and deterioration as well as transient maneuvers. Since the width of the running clearance can hardly be reduced, a new aerofoil sectional design for cantilevered vanes has been introduced to improve compressor stability over its whole range of operation. The baseline design and the new improved concept have been tested and analyzed for different clearance widths (TC1[[ellipsis]]TC3) on the rotor blades and cantilevered stator vanes. A baseline configuration featuring two-dimensional airfoils has been used as a datum to develop a more advanced design applying sweep and dihedral at the stacking axes. The running clearance on rotors and the radial gap on cantilevered stators were increased in three steps. Both numerical and experimental investigations had been carried out to verify the effect of variable running clearances on modified end wall sections. Experimental and numerical investigations have shown the effect of bow and sweep within this low speed application does not fully support the common theory of unloaded end wall sections as discussed in various publications. For the 2D blade design the common theory has been proven by both numerical and experimental evaluations. The 3D blade design configuration (BUILD IX) features a significant difference in efficiency sensitivity due to tip clearance width variation, whereas numerical prediction suggested improved compressor performance and stability. Measurements has shown higher losses at this configuration.Copyright © 2006 by ASME

Tip Leakage Flow in Radial Inflow Rotor of a Microturbine With Varying Blade-Shroud Clearance

Abstract: In this paper, tip clearance flow in a radial inflow turbine rotor under the stage environment is investigated using a three-dimensional viscous flow simulation with three different blade-shroud gap heights of 1%, 2% and 3% of the local span. The results indicate that more relative casing motion increases the scraping effect on tip leakage flow at the rotor entrance. Also, the scraping flow can dominate the whole tip clearance at the rotor entrance when the velocity is high enough at the rotor tip diameter. Regardless of the transverse mass flow rates of the three tip clearances, the results strongly exhibit the characteristics of linearity when the relative meridional length S is greater than 40%. According to the analysis of leakage flow fields in the tip clearance, measures such as a circumference slot, axial slot, or honeycomb are proposed to be applied and placed at the shroud surface over the exducer of the rotor for effectively reducing the transverse flow.Copyright © 2007 by ASME