Tip clearance

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

Effect of rotor tip clearance on the performance of a 5-inch single stage axial flow turbine

Abstract: Turbine efficiency decreased linearly with increasing rotor tip clearance. Static efficiency decreased 20 percent (0. 79 to 0. 63) as rotor tip clearance was increased from 1. 2 to 8. 0 percent of passage height. Rotor exit flow survey data are presented in addition to performance data. Comparison of data with three reference turbines substantiated the results obtained and indicated that rotor tip clearance effects are larger for a reaction turbine than for an impulse turbine. EFFECT OF ROTOR TIP CLEARANCE ON THE PERFORMANCE OF A 5-INCH SINGLE-STAGE AXIAL-FLOW TURBINE by Donald E. Holeski and Samuel M. Futral, Jr. Lewis Research Center

A Study On The Leakage Characteristics Of Tip Seal Mechanism In The Scroll Compressor

Abstract: The tip seal as a sealing mechanism to reduce the leakage flow rate through the axial clearance has been widely used in scroll compressors, but the leakage characteristics of tip seal is not well clarified due to the complicated leakage path. This paper discusses the analytical results for four theoretical models used to predict the leakage flow rate and the relationship between the changes of tip clearance and leakage flow rate under various pressure ratios. In the experiment, it was found that the tip clearance increased due to reduction of the tip sealing force that pressed the tip seal against the opposite plate under small pressure difference between upstream and downstream. Among the four models, the predicted result for the nozzle flow model was most similar to experimental result. The equivalent clearance corresponding to the measured leakage flow rate was obtained by using the nozzle model. Additionally, the behavior of tip seal forced in the tip seal groove by pressure difference was measured with a laser displacement sensor to clarify the leakage phenomenon. NOMENCLATURE Hg : height of wrap tip groove Ps : suction pressure Ht : height of tip seal Pup : upstream pressure Lg : width of wrap tip groove ∆P : differential pressure Lt : thickness of tip seal ri : inner diameter of circular wrap m& : leakage mass flow rate ro : outer diameter of circular wrap Pback : groove pressure under tip seal Tup : upstream temperature Pc : compression pressure δa : clearance between tip seal and glass plate Pd : discharge pressure δs : clearance between wrap tip and glass plate Pdn : downstream pressure e : pressure ratio of Pdn to Pup INTRODUCTION In order to attain the high efficiency of scroll compressors widely used for the air-conditioning and heat pump systems, it is greatly important to minimize the leakage flow through the narrow clearances due to the pressure difference between compression chambers. Especially, when the alternative refrigerant having highpressure properties such as R410A or CO2 is applied to the scroll compressors instead of R22, the compressor efficiency decreases due to the increase of the leakage flow caused by large pressure difference between the compression chambers. Up to now, many kinds of the models to predict the leakage flow through the narrow clearances of the compressors have been proposed, and the experimental approaches to validate the analytical models have been tried [1-9]. The scroll compressors having superior compression mechanism to any other compressors have two kinds of leakage flows. One is the radial leakage flow through the axial clearance between the scroll wrap tip and the base plate of opposite scroll, the other is the tangential leakage flow through the radial clearance between the flanks of orbiting and fixed scroll wraps. In order to reduce these leakages in scroll compressors, the sealing mechanisms to control the narrow clearances have been used. Especially, it is more important to control the axial clearance for the high efficiency because the sealing length of the axial clearance is several times longer than that of the radial clearance corresponding to wrap height. Among the sealing mechanisms to control the axial clearance, the tip seal, which is placed in the groove machined on the tip of scroll wraps, has been the most widely used due to the advantages of simple structure and good sealing ability. In the previous investigations for clarifying the leakage characteristics of tip seal mechanism, Inaba et al. [10] investigated the leakage losses about three leakage paths in the case of inserting the tip seal into a groove tightly or loosely, and they also developed the assembling techniques to insert the tip seal sufficiently close to the bottom surface of groove. On the other hand, Hirano et al. [11] clarified the sealing pressure forcing the tip seal against the base plate of opposite scroll by measuring the groove pressure under the tip seal along the scroll wrap length and measured the tip seal motion with eddy current sensors. Ancel et al. [12] investigated the dynamic behavior of two different types of tip seals, which are the multi-blade and the monobloc tip seals. Youn et al. [13] developed the experimental apparatus to measure the leakage flow using tip seal under the actual operating conditions. However, it is not enough to clarify the leakage characteristics of tip seal because of the complicated leakage path. In this study, the leakage characteristics of scroll compressors having tip seal as the sealing mechanism for the axial clearance is investigated theoretically and experimentally. The calculation using four kinds of analytical models for the estimation of the leakage flow rate is conducted. The experimental apparatus having a simplified circular wrap is set up to measure the leakage flow rate, the axial clearance and the differential pressure between upstream pressure and groove pressure under the tip seal with the various pressure ratio conditions at the same time. The calculated results are compared with the experimental ones. Moreover, the behavior of tip seal in the tip seal groove is measured directly with a laser displacement sensor to clarify the leakage phenomenon.

Measuring Rotor and Blade Dynamics Using an Optical Blade Tip Sensor

Abstract: This paper describes an optical measurement system for monitoring combustion turbine blade tips. The sensor measures distance to a blade tip using triangulation of reflected laser light. The system accomplishes triangulation using an optical position sensing device and high speed data acquisition. In this way, it is able to monitor not only average and minimum blade tip clearances, but to monitor the variations of individual blade tip clearances. By appropriate signal processing, it is possible to determine rotor vibration at the probe axial location, variations in shaft DC position, transient losses in blade tip clearance, the potential for tip and seal rubs, vibrations of individual blades in the tangential direction, and rotor torsional vibration at the probe location. Some aspects of blade and torsional vibrations would require more than one probe. The paper presents static calibration data for the measurement system, showing its degree of linearity and range. The paper also presents data obtained on a dynamic blade test rig with tip passing speeds and blade widths comparable to those encountered in high performance industrial combustion turbines. Data from this rig have been processed to show rotor vibration, shift in shaft average position, blade-to-blade tip clearance variation, and variation with speed of minimum blade tip clearance. The measurement system is designed to produce data suitable for use in the monitoring of advanced combustion turbine durability and the diagnosis of turbine functional problems, static and dynamic.© 1990 ASME

A Comparison Between the Design Point and Near Stall Performance of an Axial Compressor

Abstract: Detailed measurements have been made within an axial compressor operating both at design point and near stall. Rotor tip clearance was found to control the performance of the machine by influencing the flow within the rotor blade passages. This was not found to be the case in the stator blade row, where hub clearance was introduced beneath the blade tips. Although the passage flow was observed to be altered dramatically, no significant changes were apparent in the overall pressure rise or stall point.Small tip clearances in the rotor blade row resulted in the formation of corner separations at the hub, where the blade loading was highest. More representative clearances resulted in blockage at the tip due to the increased tip clearance flow. The effects which have been observed emphasize both the three dimensional nature of the flow within compressor blade passages, and the importance of the flow in the endwall regions in determining the overall compressor performance.Copyright © 1989 by ASME