Tip clearance

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

A Correlation of Leakage Vortex Cavitation in Axial-Flow Pumps

Abstract: Tip clearance flow in turbomachinery can lead to losses in efficiency and stall margin. In liquid handling turbomachinery, the vortical flow field, formed from the interaction of the leakage flow with the through-flow, is subject to cavitation. Furthermore, this flow field is complex and not well understood. A correlation of variables which predict the vortex minimum pressure has been formulated. Measurements of the important variables for this correlation have been made on a high Reynolds number (3×10 6 ) axial-flow test rig. The correlation has been applied to the measured data and other data sets from the literature with good agreement. An optimum tip clearance has been theoretically identified as experiments have shown

Experimental Study on the Three-Dimensional Flow Within a Compressor Cascade With Tip Clearance: Part I—Velocity and Pressure Fields

Abstract: Experimental results from a study of the three-dimensional flow in a linear compressor cascade with stationary endwall at design conditions are presented for tip clearance levels of 1.0, 2.0, and 3.3 percent of chord, compared with the no-clearance case. In addition to five-hole probe measurements, extensive surface flow visualizations are conducted. It is observed that for the smaller clearance cases a weak horseshoe vortex forms in the front of the blade leading edge. At all the tip gap cases, a multiple tip vortex structure with three discrete vortices around the midchord is found. The tip leakage vortex core is well defined after the midchord but does not cover a significant area in traverse planes. The presence of the tip leakage vortex results in the passage vortex moving close to the endwall and the suction side.

Numerical Investigation on the Self-Induced Unsteadiness in Tip Leakage Flow for a Transonic Fan Rotor

Abstract: A numerical investigation on the self-induced unsteadiness in tip leakage flow is presented for a transonic fan rotor. NASA Rotor 67 is chosen as the computational model. It is found that under certain conditions the self-induced unsteadiness can be originated from the interaction of two important driving "forces:" the incoming main flow and the tip leakage flow. Among all the simulated cases, the self-induced unsteadiness exists when the size of the tip clearance is equal to or larger than the design tip clearance. The originating mechanism of the unsteadiness is clarified through time-dependent internal flow patterns in the rotor tip region. It is demonstrated that when strong enough, the tip leakage flow impinges the pressure side of neighboring blade and alters the blade loading significantly. The blade loading in turn changes the strength of the tip leakage flow and results in a flow oscillation with a typical signature frequency. This periodic process is further illustrated by the time-space relation between the driving forces. A correlation based on the momentum ratio of tip leakage flow over the incoming main flow at the tip region is used as an indicator for the onset of the self-induced unsteadiness in tip leakage flow. It is discussed that the interaction between shock wave and tip leakage vortex does not initiate the self-induced unsteadiness, but might be the cause of other types of unsteadiness, such as broad-banded turbulence unsteadiness.

Laser Anemometer Measurements of the Flow Field in a 4:1 Pressure Ratio Centrifugal Impeller

Abstract: A laser-doppler anemometer was used to obtain flow-field velocity measurements in a 4:1 pressure ratio, 4.54 kg/s (10 lbm/s), centrifugal impeller, with splitter blades and backsweep, which was configured with a vaneless diffuser. Measured through-flow velocities are reported for ten quasi-orthogonal survey planes at locations ranging from 1% to 99% of main blade chord. Measured through-flow velocities are compared to those predicted by a 3-D viscous steady flow analysis (Dawes) code. The measurements show the development and progression through the impeller and vaneless diffuser of a through-flow velocity deficit which results from the tip clearance flow and accumulation of low momentum fluid centrifuged from the blade and hub surfaces. Flow traces from the CFD analysis show the origin of this deficit which begins to grow in the inlet region of the impeller where it is first detected near the suction surface side of the passage. It then moves toward the pressure side of the channel, due to the movement of tip clearance flow across the impeller passage, where it is cut by the splitter blade leading edge. As blade loading increases toward the rear of the channel the deficit region is driven back toward the suction surface by the cross-passage pressure gradient. There is no evidence of a large wake region that might result from flow separation and the impeller efficiency is relatively high. The flow field in this impeller is quite similar to that documented previously by NASA Lewis in a large low-speed backswept impeller.

Active Control of Tip Clearance Flow in Axial Compressors

Abstract: Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2001.