Tip clearance

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

A Prediction of 3-D Viscous Flow and Performance of the NASA Low-Speed Centrifugal Compressor

Abstract: A prediction of the three-dimensional turbulent flow in the NASA Low-Speed Centrifugal Compressor Impeller has been made. The calculation was made for the compressor design conditions with the specified uniform tip clearance gap. The predicted performance is significantly worse than that predicted in the NASA design study. This is explained by the high tip leakage flow in the present calculation and by the different model adopted for tip leakage flow mixing. The calculation gives an accumulation of high losses in the shroud/pressure-side quadrant near the exit of the impeller. It also predicts a region of meridional backflow near the shroud wall. Both of these flow features should be extensive enough in the NASA impeller to allow detailed flow measurements, leading to improved flow modelling. Recommendations are made for future flow studies in the NASA impeller.Copyright © 1990 by ASME

Turbine airfoil tip

Abstract: Optimized tip performance for turbine airfoils (10) is obtained through a sequenced manufacturing process. The turbine airfoils (10) are assembled into the dovetail slots (22) of a turbine disk (20). The tips (12) of the turbine airfoils (10) assembled in the turbine disk (20) are then measured to determine the turbine airfoils (10) that do not have adequate tip clearance. The tips (12) of those turbine airfoils (10) that do not have adequate tip clearance are then machined to obtain adequate tip clearance. Once all the turbine airfoils (10) have adequate tip clearance, environmental coatings and/or thermal barrier coatings are applied to the blade tips (12).

Effect of Tip Clearance on Compressor Performance

Abstract: The internal flow fields of two stages of a certain multi-stage axial-flow compressor have been numerically simulated with three-dimensional CFD.The simulation results agree relatively well with designed interstage parameter values.Simulation results of cases with three different tip clearances,of respectively 0.5,1.0 and 1.5 times that of the designed one,are compared with one-another.The effect of clearance size on the overall performance of the multi-stage compressor is discussed.By analyzing the internal flow field in detail,loss particularities due to tip clearance leakage are being disclosed.

Active flow control to improve the aerodynamic and acoustic performance of axial turbomachines

Abstract: The tip clearance flow of axial turbomachines is important for their aerodynamic a nd acoustic performance. The rotating instability phenomena and the tip clearance noise are observed on axial turbomachines with significant tip clearance. Previous investigations show that it is possible to reduce the tip clearance noise and improve the aerodynamic performance of the fan by mounting a turbulence generator into the tip clearance gap. In this paper it is shown that these improvements can be obtained without any modification of the tip clearance gap itself by actively controlling the tip clearance flow. To achieve this, air is injected into the gap through slit nozzles mounted flush with the inner casing wall. With steady air injection it is possible to obtain ‐ with a small injected mass flow ‐ a remarkable reduction of the noise level along with an improved aerodynamic performance. With larger injected mass flows, significant improvements of the ae rodynamic performance a re obtained at t he expense of a steep increase of the noise level. Unsteady air injection synchronized with the impeller rotation yields a significant improvement of the aerodynamic performance acc ompanied by a substantial i ncrease of the noise level. Rotating instability and tip clearance noise c an be reduced in both cases. Flow investigations with a simplified stationary 2D blade cascade show that steady air injection leads to a diminished b lade tip vortex and with it t o an improved aerodynamic performance.

Interaction Between Inlet Boundary Layer, Tip-Leakage and Secondary Flows in a Low-Speed Turbine Cascade

Abstract: An experiment has been conducted in a large-scale linear turbine cascade to examine the interaction between the inlet endwall boundary layer, tip-leakage and secondary flows. Detailed flow field measurements have been made upstream and downstream of the blade row for two values of inlet boundary layer thickness (δ*/c of about 0.015 and 0.04) together with three values of tip clearance (gap heights of 0.0, 1.5 and 5.5 percent of blade chord). In the downstream plane, the total pressure deficits associated with the tip-leakage and secondary flows were discriminated by examining the sign of the streamwise vorticity. For this case, the streamwise vorticity of the two flows have opposite signs and this proved an effective criterion for separating the flows despite their close proximity in space. It was found that with clearance the loss associated with the secondary flow was substantially reduced from the zero clearance value, in contradiction to the assumption made in most loss prediction schemes. Further work is needed, notably to clarify the influence of relative tip-wall motion which in turbines reduces the tip-leakage flow while enhancing the secondary flow.© 1994 ASME