Tip leakage flow is an important factor affecting the efficiency and stability of compressors and it is important to study the tip leakage flow model in the design and performance prediction process of turbomachinery. This paper uses three-dimensional numerical software for calculation and verification, due to its low consumption of resources. This work analyzes the existing tip clearance loss prediction model and refines it to predict the tip clearance loss considering more blade geometric parameters.

In 1990, Yaras divided the tip loss into three parts, the kinetic energy loss from the leakage flow, the gap loss and the secondary flow loss near the tip. He derived the expressions of the kinetic energy loss from the leakage flow and the gap loss from an energitic point of view. However, since the data used by Yaras to derive the prediction formula is from the Yaras-Sjolander cascade experiment, the change of the blade geometry is not considered. After analyzing the formula derivation process, it is found that the discharge coefficient  (taken as constants by Yaras) will change with the gap geometry, namely, it is related to the maximum thickness and the gap size of the blade.

In this paper, the research object are cascades with  NACA65 profile and  numerical experiments were carried out by a CFD package Numeca under the condition of Mach number equal to0.45, where the variables are the gap sizes (1%, 2%, 3%, 4%, 6% of the chord length) and the maximum thickness of blades (3%, 5%, 7%, 9%, 11% of chord length). Combined with the numerical calculation results, according to the Yaras loss prediction formula and using the similar characteristics of the  variation trend and the Planck blackbody radiation formula, the relationship between the discharge coefficient  and the maximum thickness of the blade and the tip clearance is summarized, which is integrated with the Yaras loss prediction formula to obtain the final formula. This prediction formula fits the NACA65 blade calculation fairly. The average error of 24 calculation points is 2.89%. Then the CDA062 blade tip clearance loss is predicted using the refined prediction formula and the prediction error is less than 3% at Mach numbers of 0.15, 0.45 and 0.6. Therefore, the improved formula still has a good prediction effect when the blade type and Mach number change. It is considered that within a certain range of Mach number,  maximum thickness of the blade type and tip gap size, the improved formula can give good predictions.


Improvement of a Tip Clearance Loss Prediction Model Based on Geometric Variation

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

Turbo Expo - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.