Tip clearance

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

Role of Tip Clearance Flow in Rotating Instabilities and Nonsynchronous Vibrations

Abstract: Single- and multiple-blade-passage simulations of an isolated subsonic axial compressor rotor show that flow oscillations in the tip region, known as rotating instabilities and a driver for nonsynchronous vibrations, occur when only one of the two criteria for short-length-scale rotating stall inception is satisfied. This criterion is tip clearance backflow below the trailing-edge blade tip. The flow oscillations associated with rotating instabilities most likely result from impingement of this tip clearance backflow on the rear pressure side of the blade. This phenomenon could plausibly be modeled with an impinging jet subject to a lateral pressure gradient and lateral shear flow. The findings have important practical implications on the prediction and suppression of nonsynchronous vibrations.

Tip Clearance Effects in a Turbine Rotor: Part II — Velocity Field and Flow Physics

Abstract: A comprehensive experimental investigation was undertaken to explore the flow field in the tip clearance region of a turbine rotor to understand the physics of tip leakage flow. Specifically the paper looks at its origin, nature, development, interaction with the secondary flow, and its effects on performance. The experimental study was based on data obtained using a rotating five-hole probe, Laser Doppler Velocimeter, high-response pressure probes on the casing, and static pressure taps on the rotor blade surfaces. The first part of the paper deals with the pressure field and losses. Part II presents and interprets the vorticity, velocity, and turbulence fields at several axial locations. The data provided here indicates that the tip leakage vortex originates in the last half chord. The leakage vortex is confined close to the suction surface corner near the blade tip by the relative motion of the blade and the casing, and by the secondary flow in the tip region. The tip leakage flow clings to the blade suction surface until midchord then lifts off of the suction surface to form a vortex in the last 20 percent of the blade chord. The relative motion between blades and casing leads to the development of a scraping vortex that, along with the secondary flow, reduces the propagation of the tip leakage flow into the mainflow. The rotational effects and coriolis forces modify the turbulence structure in the tip leakage flow and secondary flow as compared to cascades.

Pressure Distributions in the Tip Clearance Region of an Unshrouded Axial Turbine as Affecting the Problem of Tip Burnout

Abstract: The pressure distribution in the tip clearance region of a 2D turbine cascade was examined with reference to unknown factors which cause high heat transfer rates and burnout along the edge of the pressure surface of unshrouded cooled axial turbines.Using a special micro-tapping technique, the pressure along a very narrow strip of the blade edge was found to be 2.8 times lower than the cascade outlet pressure. This low pressure, coupled with a thin boundary layer due to the intense acceleration at gap entry, are believed to cause blade burnout. The flow phenomena causing the low pressure are of very small scale and do not appear to have been previously reported.The ultra low pressure is primarily caused by the sharp flow curvature demanded of the leakage flow at gap entry. The curvature is made more severe by the apparent attachement of the flow around the corner instead of immediately separating to increase the radius demanded of the flow. The low pressures are intensified by a depression in the suction corner and by the formation of a separation bubble in the clearance gap. The bubble creates a venturi action. The suction corner depression is due to the mainstream flow moving round the leakage and secondary vortices.Copyright © 1987 by ASME

Blade track assembly with turbine tip clearance control

Abstract: A turbine shroud or blade track assembly adapted to extend around a turbine wheel assembly is disclosed. The turbine shroud includes a carrier and a blade track coupled to the carrier. The blade track is movable between a radially-inward position having a first inner diameter and a radially-outward position having a second inner diameter larger than the first inner diameter.

Tip-Clearance and Secondary Flows in a Transonic Compressor Rotor

Abstract: The purpose of this paper is to investigate tip-clearance and secondary flows numerically in a transonic compressor rotor. The computational method used is based on the numerical integration of the Favre-Reynolds-averaged three-dimensional compressible Navier-Stokes equations, using the Launder-Sharma near-wall k-∈ turbulence closure. In order to describe the flowfield through the tip and its interaction with the main flow accurately, a fine O-grid is used to discretize the tip-clearance gap. A patched O-grid is used to discretize locally the mixing-layer region created between the jetlike flow through the gap and the main flow. An H-O-H grid is used for the computation of the main flow. In order to substantiate the validity of the results, comparisons with experimental measurements are presented for the NASA―37 rotor near peak efficiency using three grids (of 10 6 , 2 × 10 6 , and 3 × 10 6 points, with 21, 31, and 41 radial stations within the gap respectively). The Launder-Sharma k-∈ model underestimates the hub corner stall present in this configuration. The computational results are then used to analyze the interblade-passage secondary flows, the flow within the tip-clearance gap, and the mixing down-stream of the rotor. The computational results indicate the presence of an important leakage-interaction region where the leakage-vortex after crossing the passage shock-wave mixes with the pressure-side secondary flows. A second trailing-edge tip vortex is also clearly visible.