Tip clearance

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

Active Control to Improve the Aerodynamic Performance and Reduce the Tip Clearance Noise of Axial Turbomachines with Steady Air Injection into the Tip Clearance Gap

Abstract: The secondary flow over the impeller blade tips of axial fans is important for the aerodynamic and acoustic performance of the fans. Pressure coefficient and efficiency drop, and the usable range of the performance characteristic is diminished as the rotor flow stalls at higher flow rates. By applying active flow control in the tip region of the impeller, it is possible to reduce the negative effects of the tip clearance flow. In the present paper, steady air injection into the tip clearance gap is investigated. Three different air injection configurations are studied. Two configurations use up to 24 separate slit nozzles, which are evenly distributed over the circumference of the casing. In the third injection configuration, the individual nozzles are replaced by a continuous circumferential slit.

Tip Clearance Flow Interaction with Circumferential Groove Casing Treatment in a Transonic Axial Compressor

Abstract: by Mark Hamilton Ross Experimental and computational studies were conducted to study the role of the tip leakage flow in axial compressor stall and the relationship between the tip clearance flow flow field and surge margin extension from circumferential groove casing treatment. The CFD results were used to identify the existence of an interface between the approach flow and the tip-leakage flow. The experiments used a surface streaking visualization method to identify the time-averaged location of this interface as a line of zero axial shear stress at the casing. The axial position of this line, denoted xzs, moved upstream with decreasing flow coefficient in both the experiments and computations. The line was consistently located at the rotor leading edge plane at the stalling flow coefficient, regardless of inflow boundary condition. These results were successfully modeled using a control volume approach that balanced the reverse axial momentum flux of the tip-leakage flow with the momentum flux of the approach fluid. Non-uniform tip clearance measurements demonstrated that movement of the interface upstream of the rotor leading edge plane leads to the generation of short length scale rotating disturbances. Therefore, stall was interpreted as a critical point in the momentum flux balance of the approach flow and the reverse axial momentum flux of the tip-leakage flow.

A Trade-Off Study of Rotor Tip Clearance Flow in a Turbine/Exhaust Diffuser System

Abstract: In a modern gas turbine power plant, the axial exhaust diffuser accounts for up to 10% of the generator power. An unshrouded rotor, due to its highly energetic tip clearance flow, improves the pressure recovery characteristic of the exhaust diffuser, while the power production within the blading suffers a loss as a result of the tip leakage flow. In this paper, these conflicting trends are thermodynamically investigated and nondimensional expressions are derived which facilitate the task of a gas turbine system designer. Conservatively, 1% thermal efficiency gain results from elimination of the last rotor tip clearance flow. The corresponding increase in thermal efficiency of a modern gas turbine power plant due to enhanced diffuser pressure recovery is less than one percent.Copyright © 1987 by ASME

Behaviour of tip-leakage flow in an axial flow compressor rotor

Abstract: The current paper reports on investigations with an aim to advance the understanding of the flowfield near the casing of a small-scale high-speed axial flow compressor rotor. Steady three-dimensional viscous flow calculations are applied to obtain flowfields at various operating conditions. To demonstrate the validity of the computation, the numerical results are first compared with available measured data. Then, the numerically obtained flowfields are analysed to identify the behaviour of tip-leakage flow, and the mechanism of blockage generation arising from flow interactions between the tip clearance flow, the blade/casing wall boundary layers, and non-uniform main flow.The current investigation indicates that the ‘breakdown’ of the tip-leakage vortex occurs inside the rotor passage at the near stall condition. The vortex ‘breakdown’ results in the low-energy fluid accumulating on the casing wall spreads out remarkably, which causes a sudden growth of the casing wall boundary layer having a lar...