Tip clearance

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

An Approximate Analysis and Prediction Method for Tip Clearance Loss in Axial Compressors

Abstract: A simple model for loss created by the tip clearance flow in axial compressors is presented, based on an experimental programme performed in conjunction with the Dawes three-dimensional Navier-Stokes calculation method. The principal mechanism of loss (entropy creation) caused by tip leakage flow has been established to be the mixing of flows of similar speeds but different direction. Calculations who that relative motion of the endwall relative to the tip has a small effect on clearance flow. The simple model correctly predicts the magnitude of tip clearance loss and the trend with changes of tip clearance for the cascade tested. For a given geometry the loss is almost exactly proportional to the ratio of tip clearance to blade span; the loss directly associated with the clearance is smaller than often assumed.The simple model for tip clearance loss has been expressed in terms of conventional non-dimensional design variables (for example; solidity, aspect ratio, flow coefficient, loading coefficient) and from these the contribution to the overall loss of efficiency caused by tip leakage flow is conveniently represented. The trends are illustrated for a number of possible compressor design choices. Blade row loss increases more slowly than blade loading (for example diffusion factor). As a result the decrement in stage efficiency associated with clearance flow decreases as the stage loading is raised in the practical range of flow and loading coefficients.Copyright © 1993 by ASME

Influence of Blade Sweep on the Energetic Behavior of Axial Flow Turbomachinery Rotors at Design Flow Rate

Abstract: Experimental and computational studies were carried out in order to survey the energetic aspects of forward and backward sweep in axial flow rotors of low aspect ratio blading for incompressible flow It has been pointed out that negative sweep tends to increase the lift, the flow rate and the ideal total pressure rise in the vicinity of the endwalls Just the opposite tendency was experienced for positive sweep The local losses were found to develop according to combined effects of sweep near the endwalls, endwall and tip clearance losses, and profile drag influenced by re-arrangement of the axial velocity profile The forward-swept bladed rotor showed reduced total efficiency compared to the unswept and swept-back bladed rotors This behavior has been explained on the basis of analysis of flow details It has been found that the swept bladings of low aspect ratio tend to retain the performance of the unswept datum rotor even in absence of sweep correctionCopyright © 2004 by ASME

Tip Gap Variation on a Transonic Rotor in the Presence of Tip Blowing

Abstract: High stability and efficiency are the main two objectives in the design of an axial-flow compressor Stability usually reduces at higher stage loading, and the stability margin critically drops in transient operation and through the life cycle of an engine A major reason for this to happen is the growing tip gap A recirculating tip blowing casing treatment has shown the ability to enhance stability To be able to use it as a stability control system at varying tip clearances in aircraft engines, the behavior of this casing treatment at different tip clearances was considered important and investigated in this paperThe present study investigates in depth the ability of a tip blowing casing treatment to postpone stall at three different tip clearances The results prove a substantial beneficial effect for design and increased tip gaps and show some negative impact of the casing treatment for a small tip gap The study is carried out on a 15 stage research compressor The investigated rotor was already investigated with an axial-slot casing treatment for different tip gap heights at the Institute for Flight Propulsion The design of a recirculating tip blowing casing treatment is simulated with an equivalent numerical setup A tip blowing casing treatment consists of a bleed port connected to a tip blowing upstream of the rotor The streamwise pressure gradient drives the tip blowing with a high injection velocityA design speed line is simulated for three tip clearance values with and without the tip blowing casing treatment The impact of the interaction between the tip blowing and the tip gap vortex is analyzed A detailed analysis of the passage flow is conducted A comparison of the stall margin is made The study is carried out using URANS simulationsCopyright © 2014 by Rolls-Royce Deutschland Ltd & Co KG

Tip Clearance Effect on Heat Transfer and Leakage Flows on the Shroud-Wall Surface in an Axial Flow Turbine

Abstract: An axial flow turbine for a turbocharger is used as a test turbine, and the local heat transfer coefficient on the surface of the shroud is measured under uniform heat flux conditions. The nature of the tip clearance flow on the shroud surface and a flow pattern in the downstream region of the rotor blades are studied, and measurements are obtained by using a hot-wire anemometer in combination with a periodic multisampling and an ensemble averaging technique. Data are obtained under on- and off-design conditions. The effects of inlet flow angle, rotational speed and tip clearance on the local heat transfer coefficient are elucidated. The mean heat transfer coefficient is correlated with the tip clearance, and the mean velocity is calculated by the velocity triangle method for approximation. A leakage flow region exists in the downstream direction beyond the middle of the wall surface opposite the rotor blade, and a leakage vortex is recognized at the suction side near the trailing edge. 16 refs.

Measurement of blade tip clearance using an ultrasonic sensor

Abstract: This paper describes a development and evaluation of a blade tip clearance measurement system using an ultrasonic sensor. Special features of this system are; (i) it is adequate for metal and non-metal blade; (ii) it permits measurement without contact; (iii) it can work in dirty environment; and (iv) it is easy to install. Experimental results using a rotating blade test rig are described. Blade tip speed is restricted to Mach 0.18 due to the limitation of the test rig. It is concluded that the ultrasonic method is a promising candidate for an on-line clearance control of gas turbine engines.