Tip clearance

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

Influence of the Clearance Size on Rotating Instability in an Axial Compressor Stator

Abstract: In order to improve the understanding of unsteady secondary flow structures in axial turbomachines, the flow in a scaled axial compressor stator was studied. It was operated in the vicinity of the stability line and could be equipped with variable hub clearances. Results from unsteady aerodynamic and acoustic pressure measurements, high-speed Particle Image Velocimetry measurements, and turbulence resolving numerical simulations are presented. Typical characteristics of the rotating instability (RI) phenomenon were found. A parameter study varying the clearance size and the blade loading, respectively, revealed the surprising occurrence of the RI even for the stator configuration without hub clearance. This contradicts the hitherto presumption of a hub or tip clearance needed to be in place for a rotating instability to emerge

The challenge of stereo PIV measurements in the tip gap of a transonic compressor rotor with casing treatment

Abstract: This contribution is aimed at summarizing the effort taken to apply stereoscopic PIV (SPIV) measurements in the tip clearance of a transonic compressor rotor equipped with a casing treatment. A light sheet probe was placed downstream of the stator and aligned to pass the light sheet through a stator passage into the blade tip clearance of the rotor. A setup with three cameras has been used in order to record the entire 2C velocity field and the smaller area of 3C field of view at the same time instance for comparison with earlier 2C PIV results. A homogeneous seeding distribution was achieved by means of a smoke generator. The main emphasis of the SPIV measurement was to establish a data set with high spatial resolution close to the compressor casing, where the aerodynamic effects of a CT are known to be strong. The paper will discuss some major aspects of the utilized PIV data processing and point out a variety of frequently underestimated error sources that influence the overall quality of the recovered data in spite of the fact that the individual PIV recordings seemed to be of very good quality. Thus, the authors will not focus on the PIV results and related interpretation of the flow field, but on the optimization and procedures applied during setup of the experiment and data processing, respectively.

Experimental Research for Performance and Noise of Small Axial Fan

Abstract: Small axial fans have become widely used as cooling devices in recent years. Because of their increasing importance, studies have been conducted on ways to improve the performance and reduce the noise of such fans. In this report, a small axial fan with a diameter of 85 mm (a type popularity used in personal computer or workstation) was selected for further examination. The influence on aerodynamic performance and noise of such frame design parameters as blade tip clearance results in a decrease of discrete frequency noise and an increase of broad-spectrum noise. As for the most suitable design refinement in terms of fan efficiency, we found that the treatment of outlet corner roundness and altering spoke skew to the direction counter to that of fan rotation was effective.

Ceramic radial flow turbine heat shield with turbine tip seal

Abstract: A turbine engine includes a rotatable turbine having a peripheral tip and a backface. A heat shield is positioned adjacent the backface and includes an integral ring extending from a peripheral edge of the heat shield to a position spaced radially outwardly from the peripheral tip of the rotatable turbine to form a tip clearance between the ring and the peripheral tip. The turbine comprises a material having a coefficient of thermal expansion at least approximately four times greater than the coefficient of thermal expansion of the heat shield such that the turbine expands toward the ring as a result of heat within the engine, thereby reducing the tip clearance to minimize air flow along the backface and improve efficiency of the engine.