Blade Tip Leakage Loss Reduction by Means of Passive Tip Injection: Linear Cascade Wind Tunnel Results

2017 ◽  
Author(s):  
Jonas Rejek ◽  
Stefan aus der Wiesche ◽  
Reinhard Willinger
Keyword(s):  
Wind Tunnel ◽  
Turbine Blade ◽  
Working Fluid ◽  
Slight Reduction ◽  
Loss Reduction ◽  
Leakage Loss ◽  
Linear Cascade ◽  
Tip Leakage ◽  
Blade Tip ◽  
Tip Injection

In the open literature, an innovative concept for turbine blade tip leakage loss reduction by means of passive tip injection was recently proposed. The present paper presents experimental results obtained for an unshrouded turbine blade corresponding to a 50 % reaction stage. The experiments were performed in a low-speed linear cascade wind tunnel facility with air as working fluid. The effect of passive tip injection on the resulting loss was investigated by detailed five-hole-probe measurements. Cascades with three different tip gap heights and blades with and without passive injection were considered. Special attention was spent to the actual upstream conditions. The detailed flow field measurements showed that at the blade tip exit the leakage flow merged with the main flow and rolled up to a tip leakage vortex. The linear cascade wind tunnel results indicated a slight reduction of the resulting total pressure loss coefficient due to the passive tip injection. The observed tip leakage loss reduction was well comparable with the predictions of simplified analytical model.

An Innovative Passive Tip-Leakage Control Method for Axial Turbines: Linear Cascade Wind Tunnel Results

2008 ◽  
Author(s):  
Markus Hamik ◽  
Reinhard Willinger
Keyword(s):  
Wind Tunnel ◽  
Turbine Blade ◽  
Working Fluid ◽  
Leakage Flow ◽  
Turbine Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip ◽  
Tip Injection ◽  
Tip Desensitization

Depending on the blade aspect ratio, tip-leakage losses can contribute up to one third of the total losses in an axial turbine blade row. In unshrouded turbine blade rows, the radial gaps allow working fluid to pass from the pressure to the suction sides. This tip-leakage flow does not contribute to the work output of the turbine stage. Therefore, any technique which tends to reduce tip-leakage losses has the objective to decrease the flow through the tip gaps. A frequently used method of reducing the tip-leakage flow is the modification of the blade tip geometry by so-called squealers or winglets. Since this method decreases the sensitivity of tip-leakage losses on tip gap width, it is called tip desensitization. This paper presents a new method for tip desensitization: the passive blade tip injection. A low speed cascade wind tunnel is used for experimental investigations. Geometry of the turbine cascade is the up-scale of the tip section of a gas turbine rotor row. Three different gap widths in the range from 0.85% to 2.50% chord length are used. Total pressure, static pressure and flow angles are obtained by traversing a pneumatic five-hole probe about 0.3 axial chord lengths downstream of the turbine cascade. For investigations of the tip injection effect, a single blade of the cascade is modified by an injection channel. Based on experimental results, it is shown that the passive tip injection method decreases tip-leakage losses. At small tip gaps, this reduction can be rather significant. Finally, the positive influence of blade tip injection on tip-leakage losses is described by an analytical model based on the discharge coefficient.

Reduction of Turbine Blade Tip Leakage Losses and Excitation Forces by Passive Tip Injection

2015 ◽  
Author(s):  
Stefan aus der Wiesche ◽  
Maximilian Passmann ◽  
Reinhard Willinger
Keyword(s):  
Viscous Flow ◽  
Turbine Blade ◽  
Excellent Agreement ◽  
Discharge Coefficient ◽  
Loss Reduction ◽  
Analytical Expression ◽  
Tip Leakage ◽  
Blade Tip ◽  
Flow Effects ◽  
Tip Injection

The reduction of turbine blade-tip losses by means of passive tip injection was theoretically investigated. The analysis employed an analytical expression of the blade-tip discharge coefficient. The resulting blade-tip excitation forces (i. e. Thomas-Alford forces) were explicitly evaluated for unshrouded turbines with and without passive tip injection. It was found, that the Thomas-Alford coefficient for cross-force can substantially increase when the blade-tip gap was reduced. This observation can directly be explained on the basis of viscous flow effects through the gap, and it was in excellent agreement with available literature data. Due to passive tip injection, a slight decrease of the blade-tip excitation cross-force was obtained. The potential of the reduction of the cross-force due to passive tip injection was found to be comparable to the corresponding tip loss reduction.

The Development of Axial Turbine Leakage Loss for Two Profiled Tip Geometries Using Linear Cascade Data

1992 ◽  
Vol 114 (1) ◽  
pp. 198-203 ◽  
Author(s):  
J. P. Bindon ◽  
G. Morphis
Keyword(s):  
Discharge Coefficient ◽  
Separation Bubble ◽  
Tip Clearance ◽  
Loss Reduction ◽  
Analysis Method ◽  
Leakage Loss ◽  
Linear Cascade ◽  
Blade Tip ◽  
Loss Coefficients ◽  
Internal Gap

To assess the possibility of tip clearance loss reduction and to explore the nature and origin of tip clearance loss, blade tip geometries that reduce the roughly 40 percent of total loss occurring within the gap were studied. The shapes investigated aimed at reducing or avoiding the gap separation bubble thought to contribute significantly to both internal gap loss and to the endwall mixing loss. It was found that radiusing and contouring the blade at gap inlet eliminated the separation bubble and reduced the internal gap loss but created a higher mixing loss to give almost unchanged overall loss coefficients when compared with the simple sharp-edged flat-tipped blade. The separation bubble does not therefore appear to influence the mixing loss. Using a method of assessing linear cascade experimental data as though it were a rotor with work transfer, one radiused geometry, contoured to shed radial flow into the gap and reduce the leakage mass flow, was found to have a significantly higher efficiency. This demonstrates the effectiveness of the data analysis method and that cascade loss coefficient alone or gap discharge coefficient cannot be used to evaluate tip clearance performance accurately. Contouring may ultimately lead to better rotor blade performances.

scholarly journals The Development of Axial Turbine Leakage Loss for Two Profiled Tip Geometries Using Linear Cascade Data

1990 ◽  
Author(s):  
Jeffrey P. Bindon ◽  
George Morphis
Keyword(s):  
Discharge Coefficient ◽  
Separation Bubble ◽  
Tip Clearance ◽  
Loss Reduction ◽  
Analysis Method ◽  
Leakage Loss ◽  
Linear Cascade ◽  
Blade Tip ◽  
Loss Coefficients ◽  
Internal Gap

To assess the possibility of tip clearance loss reduction and to explore the nature and origin of tip clearance loss, blade tip geometries which reduce the roughly 40% of total loss occurring within the gap were studied. The shapes investigated aimed at reducing or avoiding the gap separation bubble thought to contribute significantly to both internal gap loss and to the endwall mixing loss. It was found that radiusing and contouring the blade at gap inlet eliminated the separation bubble and reduced the internal gap loss but created a higher mixing loss to give almost unchanged overall loss coefficients when compared with the simple sharp edged flat tipped blade. The separation bubble does not therefore appear to influence the mixing loss. Using a method of assessing linear cascade experimental data as though it were a rotor with work transfer, one radiused geometry, contoured to shed radial flow into the gap and reduce the leakage mass flow, was found to have a significantly higher efficiency. This demonstrates the effectiveness of the data analysis method and that cascade loss coefficient alone or gap discharge coefficient cannot be used to accurately evaluate tip clearance performance. Contouring may ultimately lead to better rotor blade performances.

Effect of Turbine Blade Tip Cooling Configuration on Tip Leakage Flow and Heat Transfer

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Sergen Sakaoglu ◽  
Harika S. Kahveci
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Gas Turbines ◽  
Thermal Response ◽  
Thermal Conditions ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

Abstract The pressure difference between suction and pressure sides of a turbine blade leads to tip leakage flow, which adversely affects the first-stage high-pressure (HP) turbine blade tip aerodynamics. In modern gas turbines, HP turbine blade tips are exposed to extreme thermal conditions requiring cooling. If the coolant jet directed into the blade tip gap cannot counter the leakage flow, it will simply add up to the pressure losses due to leakage. Therefore, the compromise between the aerodynamic loss and the gain in tip-cooling effectiveness must be optimized. In this paper, the effect of tip-cooling configuration on the turbine blade tip is investigated numerically from both aerodynamics and thermal aspects to determine the optimum configuration. Computations are performed using the tip cross section of GE-E3 HP turbine first-stage blade for squealer and flat tips, where the number, location, and diameter of holes are varied. The study presents a discussion on the overall loss coefficient, total pressure loss across the tip clearance, and variation in heat transfer on the blade tip. Increasing the coolant mass flow rate using more holes or by increasing the hole diameter results in a decrease in the area-averaged Nusselt number on the tip floor. Both aerodynamic and thermal response of squealer tips to the implementation of cooling holes is superior to their flat counterparts. Among the studied configurations, the squealer tip with a larger number of cooling holes located toward the pressure side is highlighted to have the best cooling performance.

Effect of Endwall Motion on Blade Tip Heat Transfer

2003 ◽  
Vol 125 (2) ◽  
pp. 267-273 ◽  
Author(s):  
V. Srinivasan ◽  
R. J. Goldstein
Keyword(s):  
Mass Transfer ◽  
Suction Side ◽  
Tip Clearance ◽  
Pressure Gradients ◽  
Tip Leakage Flow ◽  
Blade Loading ◽  
Linear Cascade ◽  
Tip Leakage ◽  
Blade Tip ◽  
Wind Tunnel Data

Local mass transfer measurements were conducted on the tip of a turbine blade in a five-blade linear cascade with a blade-centered configuration. The tip clearance levels ranged from 0.6 to 6.9% of blade chord. The effect of relative motion between the casing and the blade tip was simulated using a moving endwall made of neoprene mounted on the top of the wind tunnel. Data were obtained for a single Reynolds number of 2.7×105 based on cascade exit velocity and blade chord. Pressure measurements indicate that the effect of endwall motion on blade loading at a clearance of 0.6% of blade chord is to reduce the pressure gradients driving the tip leakage flow. With the introduction of endwall motion, there is a reduction of about 9% in mass transfer levels at a clearance of 0.6% of chord. This is presumably due to the tip leakage vortex coming closer to the suction side of the blade and ‘blocking the flow,’ leading to reduced tip gap velocities and hence lower mass transfer.

Controlling Leakage Flows Over a Rotor Blade Tip Using Air-Curtain Injection: Part II — Rotor Casing Film Cooling

2019 ◽  
Author(s):  
Qiang Zhao ◽  
Xing Yang ◽  
Zhao Liu ◽  
Zhenping Feng ◽  
Terrence W. Simon
Keyword(s):  
Film Cooling ◽  
Leading Edge ◽  
Cooling Effectiveness ◽  
Air Curtain ◽  
Film Cooling Effectiveness ◽  
Tip Leakage ◽  
Leakage Flows ◽  
Blade Tip ◽  
Tip Injection ◽  
Tip Leakage Flows

Abstract In modern gas turbine engines, the rotor casing region experiences high thermal loads due to complex flow structures and aerothermal effects. Thus, casing cooling is one of essential measures to ensure turbine service lifetime and performance. However, studies on heat transfer and cooling over the rotor casing with tip leakage flows are limited in the open literature during the past decades. The present work aims at controlling leakage flows over the blade tip and decreasing heat loads on the rotor casing. A novel approach proposed in a companion paper (GT2019-90232) is adopted in this paper as Part II by introducing an air-curtain injection from the rotor casing through a pair of inclined rows of discrete holes positioned in the range of 30% and 50% axial chord downstream of the blade leading edge in the casing. This air-curtain injection approach is applied to flat and recessed tips with and without tip injection to evaluate its sealing capability on tip leakage flows and film cooling effectiveness on the casing for two injection ratios of 0.7% and 1.0%. In this paper, Reynolds-averaged Navier-Stokes (RANS) simulations with Shear Stress Transport (SST) k-ω turbulence model and γ-Reθ transition model, which are validated with relevant experimental data, are performed to investigate tip leakage flows and film cooling effectiveness on the casing in a single-stage, high-pressure gas turbine engine. Results show that casing injection can reduce tip leakage mass flow effectively by changing the development and migration of tip leakage mass flows, especially when the recessed tip is applied. Adding tip injection would further reduces the tip leakage. The casing injection also provides an excellent cooling effect on the casing across rotor middle chord through trailing edge regions. In the presence of the recessed tip, coolant spreads out well on the rotor tip and the casing surfaces, resulting in better film cooling effectiveness on the casing over rotor tip leading edge. In addition, the tip injection could provide an extra cooling effect in some other regions of the casing.

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