Influence of Tip Clearance on the Inter Blade and Exit Flow Field of a Turbine Rotor Cascade
13 Jun 1994-
TL;DR: In this paper, a detailed study of flow through the blade passage and downstream of a linear turbine cascade was carried out for four cases of tip clearance including zero clearance, and a total of eight stations were chosen for inter-blade flow traversing between 5% and 95% of axial chord from leading edge.
Abstract: A detailed study of flow through the blade passage and downstream of a linear turbine cascade was carried out for four cases of tip clearance including zero clearance. Apart from inlet traverse, a total of eight stations were chosen for inter-blade flow traversing between 5% and 95% of axial chord from leading edge. Downstream flow surveys were made at distances of 106% of axial chord from the blade leading edge. Pitchwise and spanwise traverses were conducted for each tip clearance at these stations using a small five hole probe. Provision was also made for the measurement of static pressure distribution on the suction and pressure surfaces and also on the blade tip surface when clearance is present. At about 40% of axial chord from the leading edge, the presence of clearance vortex is identified inside the passage. The growth of the clearance vortex in size, its movement towards the suction surface and its increase in strength with the gap size were observed beyond 55% of axial chord till the trailing edge region. The rate of growth of the losses in the endwall region increased with clearance. Home shoe vortex was not observed for the highest clearance. The overall losses increase rapidly with clearance in the rear half of the blade.
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01 Jan 2012
TL;DR: In this article, the effect of streamwise end wall fences on the performance improvement of a turbine is studied, where fences with heights of 12 mm, 16 mm and 16 mm were attached normal to the end wall and at a half pitch away from the blades.
Abstract: In the present investigations, effect of streamwise end wall fences on the performance improvement of a turbine is studied. The fences with heights of 12 mm, 16 mm were attached normal to the end wall and at a half pitch away from the blades. A miniaturized pressure probe was traversed at the exit of the cascade from midspan to the end wall at 26 locations covering more points in the end wall region. For each spanwise location, the probe was traversed in the pitchwise direction for more than 25 points covering one blade pitch. The boundary layer fence near the end wall remains effective in changing the path of pressure side of leg of horseshoe and weaken the cross flow. The overturn in flow has reduced near the end wall when fences are incorporated while outside end wall and in loss core region, it underturns slightly as result of reduction in secondary loss. The total loss is reduced by 15%, 25% for fences of height 12 mm, and 16 mm respectively. The corresponding change was obtained in the drag and lift coefficients.
4 citations
TL;DR: In this paper, the effects of airfoil-probe tubes and its installment position on the flow field of the compressor cascade were explored, and the authors found out the mechanism that how the air-probes affect the aerodynamic characteristics of the compressors.
Abstract: To explore the effects of airfoil-probe tubes and its installment position on the flow field of the compressor cascade, and find out the mechanism that how the airfoil-probes affect the aerodynamic characteristics of the compressor cascade, this paper performed both numerical and experimental works on the same compressor cascade. The experiment mainly focused on the cases of low Mach number (Ma = 0.1), and cases with different Mach numbers (0.1, 0.3, 0.7) and different incidence angles (-5, 0, 5) are investigated by the numerical method. The case without the airfoil-probe tube was referenced as the baseline, and other three cases with the airfoil-probe tubes installed in different chordwise positions (30%, 50%, 70% of the chord length) were studied. The diameter of the airfoil-probe tube is 3mm, which is configured as 300% amplification of some particular airfoil-probe according to the geometrical similarity principle. The results show that the airfoil-probe tubes have a negative influence on the flow capacity of the cascade at all investigation points. The separations and the large scale streamwise vortices that induced by the airfoil-probe tube on the pressure side cause most the losses at the high Mach number. The influence of the airfoil-probe tube on the flow field in the vicinity of the pressure side surface is local separation at the low Mach number. The airfoil-probe tubes also have a clearly effect on the leakage flow. It decreases the mass flow of the leakage flow and weakens the intensity of the leakage vortex, but enlarges the influence area. The total pressure loss of the case that the tube is installed at the half chordwise position is generally lower than other cases especially at the high Mach number, it can even decrease the losses compared with the basic case.
4 citations
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24 May 1993
TL;DR: The origins and effects of loss in turbomachines are discussed in this article with the emphasis on trying to understand the physical origins of loss rather than on reviewing the available prediction methods.
Abstract: The origins and effects of loss in turbomachines are discussed with the emphasis on trying to understand the physical origins of loss rather than on reviewing the available prediction methods. Loss is defined in terms of entropy increase and the relationship of this to the more familiar loss coefficients is derived and discussed. The sources of entropy are in general: Viscous effects in boundary layers, viscous effects in mixing processes, shock waves and heat transfer across temperature differences. These are first discussed in general and then the results are applied to turbomachinery flows. Understanding of the loss due to heat transfer requires some discussion of cycle thermodynamics. Sections are devoted to discussing: Blade boundary layer and trailing edge loss, tip leakage loss, endwall loss, effects of heat transfer and miscellaneous losses. The loss arising from boundary layer separation is particularly difficult to quantify. Most of the discussion is based on axial flow machines but a separate section is devoted to the special problems of radial flow machines.In some cases, eg attached blade boundary layers, the loss mechanisms are well understood, but even so the loss can seldom be predicted with great accuracy. In many other cases, eg endwall loss, the loss mechanisms are still not clearly understood and prediction methods remain very dependent on correlations. The paper emphasises that the use of correlations should not be a substitute for trying to understand the origins of loss and suggests that a good physical understanding of the latter may be more valuable than a quantitative prediction.Copyright © 1993 by ASME
664 citations
TL;DR: In this article, the tip clearance loss from the leading to trailing edge of a linear turbine cascade was measured and the contributions made by mixing, internal gap shear flow, and endwall/secondary flow were identified, separated, and quantified for the first time.
Abstract: The detailed development of tip clearance loss from the leading to trailing edge of a linear turbine cascade was measured and the contributions made by mixing, internal gap shear flow, and endwall/secondary flow were identified, separated, and quantified for the first time
257 citations
"Influence of Tip Clearance on the I..." refers background in this paper
...Existence of a low pressure zone near the suction side of the blade and the flow separation inside the tip gap are noted for turbines by Graham (1986), Wadia and Booth (1982), Bindon (1987 ac), Sjolander and Amrud (1987)....
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137 citations
TL;DR: In this paper, the authors discuss the mechanisms of three-dimensional flows and the associated losses occurring near the tip endwall region of a linear turbine cascade with tip clearance, and the clearance gap sizes and the cascade incidences are chosen as the most important variables affecting the mechanisms.
Abstract: This paper discusses the mechanisms of three-dimensional flows and of the associated losses occurring near the tip endwall region of a linear turbine cascade with tip clearance. The clearance gap sizes and the cascade incidences were chosen as the most important variables affecting the mechanisms
112 citations
TL;DR: In this article, the authors present further results from a continuing study on tip leakage in axial turbines, where rotation has been simulated in a linear cascade test section by using a moving-belt tip wall.
Abstract: The paper presents further results from a continuing study on tip leakage in axial turbines. Rotation has been simulated in a linear cascade test section by using a moving-belt tip wall. Measurements were made inside the tip gap with a three-hole pressure probe for a clearance size of 3.8 percent of the blade chord. Two wall speeds are considered and the results are compared with the case of no rotation. As in other experiments, significant reduction in the gap mass flow rate is observed due to the relative motion
80 citations