Tip clearance

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

Gas turbine engine having a minimal blade tip clearance

Abstract: A gas turbine engine is so constructed that the clearance or gap between the rotor and stator, especially at the outer diameter range of a radial flow end stage, is optimally maintained under all operating conditions. For this purpose the housing in the axial-flow/radial-flow compressor is constructed as a two shell housing. The outer housing shell is mounted as part of the engine structure, whereby the inner housing shell is exposed substantially only to forces or loads caused by compressor fluid flow. The material of the outer housing shell has a heat expansion coefficient in the axial direction of the rotational engine axis, which is distinctly lower than the heat expansion coefficient of the material of the compressor rotor. The heat expansion coefficient of the material of the inner housing shell is lower in the circumferential direction and approximately equal in the axial direction relative to the heat expansion coefficient of the rotor. The fixed bearing of the compressor rotor is arranged in the zone of the compressor inlet.

Measurement of Blade Tip Heat Transfer and Leakage Flow in a Turbine Cascade With a Multi-Cavity Squealer Tip

Abstract: Tip leakage flow induces high heat transfer to the blade tip and causes significant aerodynamic losses. In this paper, we propose a multi-cavity squealer tip with an additional rib in the squealer cavity. Our study investigated the effects of the rib location and shape on the blade tip heat transfer and the total pressure loss. Experiments were performed in a five-bladed linear cascade using a low speed wind tunnel. The blade chord, pitch, and span length were 126mm, 102.7mm, and 160mm, respectively. The Reynolds number, based on the blade chord and cascade exit velocity, was 2.44×105, and a tip clearance of 1.25% of the blade span was considered. The additional rib was installed in the squealer tip cavity near the leading edge, the mid-chord, and the training edge, respectively. The shape of the rib was also varied from rectangular to triangular in order to minimize the rib surface area exposed to the hot gas. The secondary flow and total pressure loss were measured using a seven-hole probe at one-chord downstream of the blade trailing edge, and the heat transfer coefficient distributions were measured by utilizing the hue-detection based transient liquid crystal technique. Flow measurement results indicated that the proposed multi-cavity tip reduced the total pressure loss. The blade tip heat transfer measurement results showed that the proposed multi-cavity tip was able to reduce the maximum heat transfer region near the cavity floor near the leading edge, but the heat transfer on the second cavity floor increased due to the leakage flow reattachment.Copyright © 2013 by ASME

A Numerical Comparison of Four Operating Conditions in a Kaplan Water Turbine, Focusing on Tip Clearance Flow

Abstract: A parallel multiblock finite volume CFD (Computational Fluid Dynamics) code CALC-PMB[3, 10, 11] (Parallel MultiBlock) for computations of turbulent flo w in complex domains has been developed and used for the computations of the flo w through a Kaplan water turbine. The computations are including both the guide vanes and the runner, where the runner computations get the inlet boundary conditions from the circumferentially averaged properties of the guide vane computations. Four different operating conditions have been computed and the results from the computations are compared. The computational results are in accordance with observations done by the the turbine manufacturer. This work is focused on tip clearance flo w, which reduces the efficienc y of the turbine by about 0.5%.

Nonuniform Flow in a Compressor Due to Asymmetric Tip Clearance

Abstract: This paper presents an analytical study of flow redistribution in a compressor stage due to asymmetric tip clearance distribution. The entire stage is modeled as an actuator disk and it is assumed that upstream and downstream flow fields are determined by the local tip clearance. The flow is assumed to be inviscid and incompressible. First, an axisymmetric flow model is used to connect upstream and downstream flows. Second, a linear perturbation approximation is used for nonaxisymmetric analysis in which each flow variable is assumed to consist of a mean (axisymmetric value) plus a small perturbation (asymmetric value). Thus, the perturbations in velocity and pressure induced by the tip clearance asymmetry are predicted. Furthermore, rotordynamic effects of such flow nonuniformity are examined as well.

The effect of spatial wandering on experimental laser velocimeter measurements of the end-wall vortices in an axial-flow pump

Abstract: In a high Reynolds number axial-flow pump, laser velocimeter (LV) measurements were made to study the size and structure of the end-wall vortex. The time mean measurements show that the core size of the end-wall vortex increased with decreasing tip clearance, which is contrary to existing theory. Observations of cavitation in the vortex showed that the flow was unsteady. The vortices emanating from the smaller clearances were observed to wander or meander spatially and to develop kinks more than the vortices emanating from the larger tip clearances. This observed unsteadiness has a significant effect on the time mean size and velocity distribution of the vortex as measured with the LV employing the field point measurement technique. In order to obtain an estimate of the true size and velocity distribution, computational experiments were conducted which modelled a periodically wandering vortex and the LV measurement process. The computational and experimental results show good agreement, including a broadened and reduced tangential velocity distribution. In this paper, the end-wall vortex LV measurements are presented, and the method of analyzing the vortex wandering is described.