The Effect of Tip Clearance Height on the Three-Dimensional Flow and Aerodynamic Loss in the Wake Region of a High-Turning Turbine Rotor Cascade

Tip clearance losses represent a major efficiency penalty of turbine blades. This paper describes the effect of tip clearance on the aerodynamic characteristics of an unshrouded axial-flow turbine cascade under very low Reynolds number conditions. The Reynolds number based on the true chord length and exit velocity of the turbine cascade was varied from 4.4×104 to 26.6×104 by changing the velocity of fluid flow. The freestream turbulence intensity was varied between 0.5% and 4.1% by modifying turbulence generation sheet settings. Three-dimensional flow fields at the exit of the turbine cascade were measured both with and without tip clearance using a five-hole pressure probe. Tip leakage flow generated a large high total pressure loss region. Variations in the Reynolds number and freestream turbulence intensity changed the distributions of three-dimensional flow, but had no effect on the mass-averaged tip clearance loss of the turbine cascade.

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Three-Dimensional Flow and Mixing in an Axial Flow Compressor With Different Rotor Tip Clearances

Journal of Turbomachinery ◽

10.1115/1.2929192 ◽

1992 ◽

Vol 114 (3) ◽

pp. 675-685 ◽

Cited By ~ 35

Author(s):

A. Goto

Keyword(s):

Velocity Fluctuation ◽

Three Dimensional ◽

Axial Flow ◽

Flow Fields ◽

Tip Clearance ◽

Small Scale ◽

Three Dimensional Flow ◽

Axial Flow Compressor ◽

Dimensional Flow ◽

Flow Compressor

The effect of difference in rotor tip clearance on the mean flow fields and unsteadiness and mixing across a stator blade row were investigated using hot-wire anemometry, pressure probes, flow visualization, and the ethylene tracer-gas technique on a single-stage axial flow compressor. The structure of the three-dimensional flow fields was discussed based on results of experiments using the 12-orientation single slanted hotwire technique and spectrum analysis of velocity fluctuation. High-pass filtered measurements of turbulence were also carried out in order to confirm small-scale velocity fluctuation, which is more realistically referred to as turbulence. The span-wise distribution of ethylene gas spreading, estimated by the measured small-scale velocity fluctuation at the rotor exit, agreed quite well with that which was experimentally measured. This fact suggests the significant role of turbulence, generated within the rotor, in the mixing process across the downstream stator. The value of the maximum mixing coefficient in the tip region was found to increase linearly as the tip clearance became enlarged, starting from the value at midspan.

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Three-Dimensional-Flow Theories for Axial Compressors and Turbines

Proceedings of the Institution of Mechanical Engineers ◽

10.1243/pime_proc_1948_159_023_02 ◽

1948 ◽

Vol 159 (1) ◽

pp. 255-268 ◽

Cited By ~ 19

Author(s):

A. D. S. Carter

Keyword(s):

Three Dimensional ◽

Axial Compressor ◽

Physical Nature ◽

Secondary Flows ◽

Operating Conditions ◽

Tip Clearance ◽

Three Dimensional Flow ◽

Axial Compressors ◽

Dimensional Flow ◽

Blade Row

It has long been known that the energy losses occurring in an axial compressor or turbine cannot be fully accounted for by the skin-friction losses on the blades and annulus walls. The difference, usually termed secondary loss, is attributed to miscellaneous secondary flows which take place in the blade row. These flows both cause losses in themselves and modify the operating conditions of the individual blade sections, to the detriment of the overall performance. This lecture analyses the three-dimensional flow in axial compressors and turbines, so that, by appreciation of the factors involved, possible methods of improving the performance can readily be investigated. The origin of secondary flow is first examined for the simple case of a straight cascade. The physical nature of the flow, and theories which enable quantitative estimates to be made, are discussed at some length. Following this, the three-dimensional flow in an annulus with a stationary blade row is examined, and, among other things, the influence of radial equilibrium on the flow pattern is noted. All physical restrictions are then removed, and the major factors governing the three-dimensional flow in an actual machine are investigated as far as is possible with existing information, particular attention being paid to the influence of a non-uniform velocity profile, tip clearance, shrouding, and boundary layer displacement. Finally the various empirical factors used in design are discussed, and the relationships between them established.

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Effects of Reynolds Number and Free-Stream Turbulence on Turbine Tip Clearance Flow

Volume 6: Turbo Expo 2005, Parts A and B ◽

10.1115/gt2005-68009 ◽

2005 ◽

Author(s):

Takayuki Matsunuma

Keyword(s):

Reynolds Number ◽

Turbulence Intensity ◽

Free Stream ◽

Three Dimensional ◽

Tip Clearance ◽

Turbine Cascade ◽

Tip Leakage Flow ◽

Three Dimensional Flow ◽

Free Stream Turbulence ◽

Dimensional Flow

Tip clearance losses represent a major efficiency penalty of turbine blades. This paper describes the effect of tip clearance on the aerodynamic characteristics of an unshrouded axial-flow turbine cascade under very low Reynolds number conditions. The Reynolds number based on the true chord length and exit velocity of the turbine cascade was varied from 4.4 × 104 to 26.6 × 104 by changing the velocity of fluid flow. The free-stream turbulence intensity was varied between 0.5% and 4.1% by modifying turbulence generation sheet settings. Three-dimensional flow fields at the exit of the turbine cascade were measured both with and without tip clearance using a five-hole pressure probe. Tip leakage flow generated a large high total pressure loss region. Variations in the Reynolds number and free-stream turbulence intensity changed the distributions of three-dimensional flow, but had no effect on the mass-averaged tip clearance loss of the turbine cascade.

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Experimental Study on the Three-Dimensional Flow Within a Compressor Cascade With Tip Clearance: Part I—Velocity and Pressure Fields

Journal of Turbomachinery ◽

10.1115/1.2929270 ◽

1993 ◽

Vol 115 (3) ◽

pp. 435-443 ◽

Cited By ~ 40

Author(s):

S. Kang ◽

C. Hirsch

Keyword(s):

Three Dimensional ◽

Leading Edge ◽

Surface Flow ◽

Tip Clearance ◽

Tip Vortex ◽

Compressor Cascade ◽

Three Dimensional Flow ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Dimensional Flow

Experimental results from a study of the three-dimensional flow in a linear compressor cascade with stationary endwall at design conditions are presented for tip clearance levels of 1.0, 2.0, and 3.3 percent of chord, compared with the no-clearance case. In addition to five-hole probe measurements, extensive surface flow visualizations are conducted. It is observed that for the smaller clearance cases a weak horseshoe vortex forms in the front of the blade leading edge. At all the tip gap cases, a multiple tip vortex structure with three discrete vortices around the midchord is found. The tip leakage vortex core is well defined after the midchord but does not cover a significant area in traverse planes. The presence of the tip leakage vortex results in the passage vortex moving close to the endwall and the suction side.

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