Endwall Profiling With Tip Clearance Flows

2012 ◽  
Author(s):  
Michael Hilfer ◽  
Grant Ingram ◽  
Simon Hogg
Keyword(s):  
Aspect Ratio ◽  
Design Process ◽  
Experimental Validation ◽  
Tip Clearance ◽  
Design System ◽  
Tip Clearance Flow ◽  
Linear Cascade ◽  
Low Speed ◽  
Clearance Flow

This paper describes the design of a non-axisymmetric profiled endwall with tip clearance flow. Previous designs have assumed that the interaction between the tip clearance flow and the endwall has been negligible and this paper allows this assumption to be tested. A profiled endwall was designed, built and tested in a low speed linear cascade. The design was conducted using the Durham endwall design system and this paper provides details of the first experimental validation of this system. Overall the design system was found to perform successfully. Many other researchers have conducted endwall design, test and build exercises and the key advance here was to examine the effect of profiled endwalls on tip clearance flow. To this end a tip clearance was added to both the CFD and the cascade during the design process. The results show that even with an aspect ratio of two the endwall produces noticeable changes on the tip clearance flow. This does not however necessarily prevent a successful profiled endwall from being implemented in the cascade.

Tip Clearance Flow Induced Endwall Boundary Layer Separation in a Single–Stage Axial–Flow Low–Speed Compressor

2000 ◽  
Author(s):  
Horst Saathoff ◽  
Udo Stark
Keyword(s):  
Axial Flow ◽  
Boundary Layer Separation ◽  
Single Stage ◽  
Tip Clearance ◽  
Compressor Cascade ◽  
Tip Clearance Flow ◽  
Low Speed ◽  
Pressure Distributions ◽  
Oil Flow ◽  
Clearance Flow

The paper describes an investigation of the overtip end-wall flow in a single–stage axial–flow low–speed compressor utilizing an oil flow technique and a periodic multisampling pressure measurement technique. Representative oil flow pictures and ensemble averaged casingwall pressure distributions with standard deviations — supplemented by selected endwall oil flow pictures from a corresponding 2D compressor cascade — are shown and carefully analysed. The results enable the key features of the overtip endwall flow to be identified and changes with flow rate — or inlet angle — to be determined.

Investigation of Unsteady Flow Field in a Low-Speed One and a Half Stage Axial Compressor: Effects of Tip Gap Size on the Tip Clearance Flow Structure at Near Stall Operation

2014 ◽  
Author(s):  
Chunill Hah ◽  
Michael Hathaway ◽  
Joseph Katz
Keyword(s):  
Unsteady Flow ◽  
Flow Structure ◽  
Flow Instability ◽  
Axial Compressor ◽  
Leading Edge ◽  
Tip Clearance ◽  
Tip Clearance Flow ◽  
Low Speed ◽  
Clearance Flow ◽  
Tip Clearance Vortex

The primary focus of this paper is to investigate the effect of rotor tip gap size on how the rotor unsteady tip clearance flow structure changes in a low speed one and half stage axial compressor at near stall operation (for example, where maximum pressure rise is obtained). A Large Eddy Simulation (LES) is applied to calculate the unsteady flow field at this flow condition with both a small and a large tip gaps. The numerically obtained flow fields at the small clearance matches fairly well with the available initial measurements obtained at the Johns Hopkins University with 3-D unsteady PIV in an index-matched test facility which renders the compressor blades and casing optically transparent. With this setup, the unsteady velocity field in the entire flow domain, including the flow inside the tip gap, can be measured. The numerical results are also compared with previously published measurements in a low speed single stage compressor (Maerz et al. [2002]). The current study shows that, with the smaller rotor tip gap, the tip clearance vortex moves to the leading edge plane at near stall operating condition, creating a nearly circumferentially aligned vortex that persists around the entire rotor. On the other hand, with a large tip gap, the clearance vortex stays inside the blade passage at near stall operation. With the large tip gap, flow instability and related large pressure fluctuation at the leading edge are observed in this one and a half stage compressor. Detailed examination of the unsteady flow structure in this compressor stage reveals that the flow instability is due to shed vortices near the leading edge, and not due to a three-dimensional separation vortex originating from the suction side of the blade, which is commonly referred to during a spike-type stall inception. The entire tip clearance flow is highly unsteady. Many vortex structures in the tip clearance flow, including the sheet vortex system near the casing, interact with each other. The core tip clearance vortex, which is formed with the rotor tip gap flows near the leading edge, is also highly unsteady or intermittent due to pressure oscillations near the leading edge and varies from passage to passage. For the current compressor stage, the evidence does not seem to support that a classical vortex breakup occurs in any organized way, even with the large tip gap. Although wakes from the IGV influence the tip clearance flow in the rotor, the major characteristics of rotor tip clearance flows in isolated or single stage rotors are observed in this one and a half stage axial compressor.

Experiments and Computations on Large Tip Clearance Effects in a Linear Cascade

2008 ◽  
Author(s):  
Richard Williams ◽  
David Gregory-Smith ◽  
Li He ◽  
Grant Ingram
Keyword(s):  
Gas Turbines ◽  
Tip Clearance ◽  
Computational Techniques ◽  
Tip Clearance Flow ◽  
Linear Cascade ◽  
Pressure Surface ◽  
Controlled Diffusion ◽  
Clearance Flow ◽  
Industrial Gas Turbines ◽  
Tip Clearance Vortex

Large tip clearances typically in the region of six percent exist in the high pressure stages of compressors of industrial gas turbines. Due to the relatively short annulus height and significant blockage, the tip clearance flow accounts for the largest proportion of loss in the HP. Therefore increasing the understanding of such flows will allow for improvements in design of such compressors, increasing efficiency, stability and the operating range. Experimental and computational techniques have been used to increase the physical understanding of the tip clearance flows through varying clearances in a linear cascade of controlled-diffusion blades. This paper shows two unexpected results. Firstly the loss does not increase with clearances greater than 4% and secondly there is an increase of blade loading towards the tip above 2% clearance. It appears that the loss production mechanisms of the pressure driven tip clearance jet do not increase as the clearance is increased to large values. The increase in blade force is attributed to the effect of the strong tip clearance vortex which does not move across the blade passage to the pressure surface, as is often observed for high stagger blading. These results may be significant for the design of HP compressors for industrial gas turbines.

Experiments and Computations on Large Tip Clearance Effects in a Linear Cascade

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Richard Williams ◽  
David Gregory-Smith ◽  
Li He ◽  
Grant Ingram
Keyword(s):  
Gas Turbines ◽  
Tip Clearance ◽  
Computational Techniques ◽  
Tip Clearance Flow ◽  
Linear Cascade ◽  
Pressure Surface ◽  
Controlled Diffusion ◽  
Clearance Flow ◽  
Industrial Gas Turbines ◽  
Tip Clearance Vortex

Large tip clearances typically in the region of 6% exist in the high pressure (HP) stages of compressors of industrial gas turbines. Due to the relatively short annulus height and significant blockage, the tip clearance flow accounts for the largest proportion of loss in the HP. Therefore increasing the understanding of such flows will allow for improvements in design of such compressors, increasing efficiency, stability, and the operating range. Experimental and computational techniques have been used to increase the physical understanding of the tip clearance flows through varying clearances in a linear cascade of controlled-diffusion blades. This paper shows two unexpected results. First the loss does not increase with clearances greater than 4% and second there is an increase in blade loading toward the tip above 2% clearance. It appears that the loss production mechanisms of the pressure driven tip clearance jet do not increase as the clearance is increased to large values. The increase in blade force is attributed to the effect of the strong tip clearance vortex, which does not move across the blade passage to the pressure surface, as is often observed for high stagger blading. These results may be significant for the design of HP compressors for industrial gas turbines.

Experimental Study on Different Tip Clearance of Low-Speed Axial Fan

2021 ◽  
Author(s):  
Ming Zhang ◽  
Jia Li ◽  
Xu Dong ◽  
Dakun Sun ◽  
Xiaofeng Sun
Keyword(s):  
Experimental Studies ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Signal Spectrum ◽  
Tip Clearance Flow ◽  
Low Speed ◽  
Clearance Flow ◽  
Casing Pressure

Abstract Tip clearance flow is not only the source of undesirable noise but also a potential indicator for critical operating conditions with rotating stall or surge. It can induce blade vibration, which would cause premature blade failure when the vibration is strong enough. The paper presents experimental studies on the effects of tip clearance on the stall inception process in a low-speed high-load single stage fan with different tip clearance. From the point of view of flow range, it has been proved by computations that there is an optimal gap value, and an explanation is given according to different stall mechanisms of large and small tip clearance. However, the experiment of no tip clearance is not easy to achieve. In this experiment, a wearable soft wall casing was used to achieve “zero clearance”, and an explicit conclusion was obtained. The pressure rise and efficiency are improved at small tip clearance. Instantaneous Casing Pressure Field Measurement was carried out: instantaneous casing pressure fields were measured by 9 high response pressure transducers mounted on the casing wall. At the near stall point with large tip clearance, a narrow band increase of the amplitudes in the frequency spectrum at roughly half of the blade passing frequency can be observed according to the spectrum of static pressure at points on the endwall near the leading-edge and above the rotor. This phenomenon was explained from two aspects: tip clearance flow structure and pressure signal spectrum.

Unsteady Tip Clearance Flow in a Low-Speed Axial Compressor Rotor With Upstream and Downstream Stators

2005 ◽  
Author(s):  
Xiangyang Deng ◽  
Hongwu Zhang ◽  
Jingyi Chen ◽  
Weiguang Huang
Keyword(s):  
Flow Behavior ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Tip Clearance ◽  
Gap Size ◽  
Tip Clearance Flow ◽  
Low Speed ◽  
Compressor Rotor ◽  
Clearance Flow ◽  
Unsteady Effect

In the course of advancing the understanding of the unsteady flow nature of compressor tip clearance flows, the present paper investigates the unsteady tip clearance flow in the second rotor of a two-stage low-speed axial compressor and its interaction with upstream and downstream stators. Numerical methods were adopted in the present study and the research focused on clarifying the unsteadiness of tip clearance flow behavior and its link to the change of rotor performance, subjected to the variables of axial gap sizes between the rotor and upstream and downstream stators. The result shows how and why the tip leakage vortex trajectory changes its shape with the change of gap size, and its impact on the rotor pressure rise characteristic. Within all the computed operating range, the pressure rise increases monotonically with the decrease of upstream axial gaps, but no monotonic variation was observed with the change of downstream axial gaps. This trend of performance change could be explained by the unsteady effect of upstream stator wakes, and the overall result is that the rotor performance was found to be more influenced by the upstream interaction than the downstream interaction. The frequency characteristic of the tip clearance vortex, under the influence of gap size and compressor operating condition, was also analyzed to provide a quantified estimation of its periodic flow behavior and a comparison with the recent results of other researchers.

Investigation of a Tip Clearance Cascade in a Water Analogy Rig

1986 ◽  
Vol 108 (1) ◽  
pp. 38-46 ◽  
Author(s):  
J. A. H. Graham
Keyword(s):  
Turbine Blades ◽  
Flow Region ◽  
Tip Clearance ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Tip Clearance Flow ◽  
Pressure Profiles ◽  
Clearance Flow ◽  
Hot Film ◽  
Model Features

The tip clearance flow region of high-pressure axial turbine blades for small gas turbine engines has been investigated in a water flow cascade. The blade model features variable clearance and variable endwall speeds. The cascade is scaled for Reynolds number and sized to give velocities suitable for visualization. Pressure profiles were measured on one blade, and correlated with the visualization. Unloading is found to be a major feature of the pressure field at both tip and midspan, and is intimately connected with scraping effects and the behavior of the clearance vortex. Some initial hot-film velocity measurements are also presented.

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