Parametrical Investigation of Turbine Stages With Open Tip Clearance for the Purpose of Stage Efficiency Increase

2010 ◽  
Author(s):  
Andrei Granovskiy ◽  
Mikhail Kostege ◽  
Nikolay Lomakin
Keyword(s):  
Pressure Ratio ◽  
Axial Flow ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Turbine Stage ◽  
Suction Surface ◽  
Tip Leakage ◽  
Degree Of Reaction ◽  
Blade Tip ◽  
Stage Efficiency

The aerodynamic loss due to tip leakage vortex of rotor blades represents a significant part of viscous losses in axial flow turbines. The mixing of leakage flow with the main rotor passage flow causes losses and reduces turbine stage efficiency. Many measures have been proposed to reduce the loss in the tip clearance area. In this paper the reduction of the tip clearance loss due to changes made to the blade tip section profile is presented. The blade tip profile was modified to decrease the pressure gradient between pressure surface and suction surface. This approach allows the reduction of tip leakage and tip vortex strength and consequently the reduction of tip clearance losses. A 3D Navier-Stokes solver with q-ω turbulence model is used to analyze the flow in the turbine with various tip section profiles. Test data of three single-stage experimental turbines have been used to validate analytical predictions: • Highly loaded turbine stage with a pressure ratio π0T = 3.2 and reaction degree ρmean = 0.5. • Two turbines with a pressure ratio π0T = 3.9. (One with high degree of reaction ρmean = 0.55; the other with low degree of reaction ρmean = 0.26). The numerical investigation of the influence of various tip section profiles on stage efficiency was carried out in the range of relative tip clearance 0.5%–2.4% with the objective of a decreasing the influence of the tip clearance on the stage efficiency.

Transonic Passage Turbine Blade Tip Clearance With Scalloped Shroud: Part II — Losses With and Without Scrubbing Effects in Engine Configuration

2004 ◽  
Author(s):  
Wayne S. Strasser ◽  
Gregory M. Feldman ◽  
F. Casey Wilkins ◽  
James H. Leylek
Keyword(s):  
Turbine Blade ◽  
Turbulence Model ◽  
Large Scale ◽  
Pressure Ratio ◽  
Viscous Sublayer ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Tip Leakage ◽  
Passage Vortex ◽  
Blade Tip

Loss mechanisms in a scallop shrouded transonic power generation turbine blade passage at realistic engine conditions have been identified through a series of large-scale (typically 12 million finite volumes) simulations. All simulations are run with second-order discretization and viscous sublayer resolution, and they include the effects of viscous dissipation. The mesh (y+ near unity on all surfaces) is highly refined in the tip clearance region, casing recesses, and shroud region in order to fully capture complex interdependent flow physics and the associated losses. Aerodynamic losses, in order of their relative importance, are a result of the following: separation around the tip, recesses, and shroud; tip vortex creation; downstream mixing losses, localized shocks on the airfoil; and the passage vortex emanating from under the shroud. A number of helical lateral flows were established near the upper shroud surfaces as a result of lateral pressure gradients on the scalloped shroud. It was found that the tip leakage and passage losses increased approximately linearly with increasing tip clearance, both with and without the effect of the relative casing motion. For each tip clearance studied, scrubbing slightly reduced the tip leakage, but the overall production of entropy was increased by more than 50%. Also the overall passage mass flow rate, for a given inlet total pressure to exit static pressure ratio, increased almost linearly with increasing tip clearance. In addition, it was also found that there was slight positive and negative lift on the shroud, depending on the tip clearance. At the lowest tip clearance of 20 mils there was a negative lift on the shroud. In the 200-mil tip clearance case there was a positive lift on the shroud. The relative motion of the casing contributed positively to the lift at every tip clearance, affecting more at the lowest tip clearance where the casing is closest to the blade tip. Lastly, it was found that the computed entropy generation for the stationary 80-mils case using the SKE turbulence model was close to that of the 80-mils scrubbing case using the RKE turbulence model. In light of the proposed mechanisms and their relative contributions, suggested design considerations are posed.

scholarly journals Effects of Tip Clearance and Casing Recess on Heat Transfer and Stage Efficiency in Axial Turbines

1998 ◽  
Author(s):  
A. A. Ameri ◽  
E. Steinthorsson ◽  
David L. Rigby
Keyword(s):  
Heat Transfer ◽  
Suction Side ◽  
Tip Clearance ◽  
Flow Conditions ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip ◽  
Axial Turbines ◽  
Gap Height ◽  
Stage Efficiency

Calculations were performed to assess the effect of the tip leakage flow on the rate of heat transfer to blade, blade tip and casing. The effect on exit angle and efficiency was also examined. Passage geometries with and without casing recess were considered. The geometry and the flow conditions of the GE-E3 first stage turbine, which represents a modern gas turbine blade were used for the analysis. Clearance heights of 0%, 1%, 1.5% and 3% of the passage height were considered. For the two largest clearance heights considered, different recess depths were studied. There was an increase in the thermal load on all the heat transfer surfaces considered due to enlargement of the clearance gap. Introduction of recessed casing resulted in a drop in the rate of heat transfer on the pressure side but the picture on the suction side was found to be more complex for the smaller tip clearance height considered. For the larger tip clearance height the effect of casing recess was an orderly reduction in the suction side heat transfer as the casing recess height was increased. There was a marked reduction of heat load and peak values on the blade tip upon introduction of casing recess, however only a small reduction was observed on the casing itself. It was reconfirmed that there is a linear relationship between the efficiency and the tip gap height. It was also observed that the recess casing has a small effect on the efficiency but can have a moderating effect on the flow underturning at smaller tip clearances.

Effects of Tip Clearance on Unsteady Flow Characteristics in an Axial Turbine Stage

2009 ◽  
Author(s):  
Hao Sun ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Rotor Blade ◽  
Suction Side ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

The clearance between the rotor blade tip and casing wall in turbomachinery passages induces leakage flow loss and thus degrades aerodynamic performance of the machine. The flow field in turbomachinery is significantly influenced by the rotor blade tip clearance size. To investigate the effects of tip clearance size on the rotor-stator interaction, the turbine stage profile from Matsunuma’s experimental tests was adopted, and the unsteady flow fields with two tip clearance sizes of 0.67% and 2.00% of blade span was numerical simulated based on Harmonic method using NUMECA software. By comparing with the domain scaling method, the accuracy of the harmonic method was verified. The interaction mechanism between the stator wake and the leakage flow was investigated. It is found that the recirculation induced by the stator wake is separated by a significant “interaction line” from the flow field close to the suction side in the clearance region. The trend of the pressure fluctuation is contrary on both sides of the line. When the stator wakes pass by the suction side, the pressure field fluctuates and the intensity of the tip leakage flow varies. With the clearance size increasing, the “interaction line” is more far away from the suction side and the intensity of tip leakage flow also fluctuates more strongly.

scholarly journals Evaluating the Aerodynamic Impact of Circumferentially Grooved Fan Casing Treatments With Integrated Acoustic Liners on a Turbofan Rotor

2019 ◽  
Author(s):  
Richard F. Bozak ◽  
Gary G. Podboy
Keyword(s):  
Pressure Ratio ◽  
Aerodynamic Performance ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Fan Noise ◽  
Tip Leakage ◽  
Fan Performance ◽  
Acoustic Liners ◽  
Rotor Stator Interaction ◽  
Real Gas Effects

Abstract NASA is investigating the potential of integrating acoustic liners into fan cases to reduce fan noise, while maintaining the fans aerodynamic performance. An experiment was conducted to quantify the aerodynamic impact of circumferentially grooved fan cases with integrated acoustic liners on a 1.5 pressure ratio turbofan rotor. In order to improve the ability to measure small performance changes, fan performance calculations were updated to include real gas effects including the effect of humidity. For all fan cases tested, the measured difference in fan isentropic efficiency was found to be less than the measurement repeatability for a torque-based efficiency calculation (≈ 0.2%), however, an unintended tip clearance difference between configurations makes it difficult to determine if circumferentially grooved fan cases degraded fan performance. Fan exit turbulence measurements showed a 1.5% reduction in total turbulence intensity between hardwall and circumferentially grooved fan cases in the tip vortex region, which is attributed to a disruption in the formation of the tip leakage vortex. This decrease in fan exit turbulence could potentially lead to a 1–2dB reduction in broadband rotor-stator interaction noise. Reduced aerodynamic performance losses associated with over-the-rotor liners could enable further fan noise reduction.

Time-Averaged Heat Flux for a Recessed Tip, Lip, and Platform of a Transonic Turbine Blade

2000 ◽  
Author(s):  
M. G. Dunn ◽  
C. W. Haldeman
Keyword(s):  
Heat Flux ◽  
Pressure Ratio ◽  
Design Flow ◽  
Turbine Stage ◽  
Suction Surface ◽  
Surface Measurements ◽  
Blade Tip ◽  
Flux Level ◽  
Transonic Turbine ◽  
Exit Mach Number

The results of an experimental research program determining the blade platform heat-flux level and the influence of blade tip recess on the tip region heat transfer for a full-scale rotating turbine stage at transonic vane exit conditions are described. The turbine used for these measurements was the Allison VBI stage operating in the closed vane position (vane exit Mach number _ 1.1). The stage was operated at the design flow function, total to static pressure ratio, and corrected speed. Measurements were obtained at several locations on the platform and in the blade tip region. The tip region consists of the bottom of the recess, the lip region (on both the pressure and suction surface sides of the recess), and the 90% span location on the blade suction surface. Measurements were obtained for three vane/blade spacings; 20%, 40%, and 60% of vane axial chord and for a single value of the tip gap (the distance between the top of the lip and the stationary shroud) equal to 0.0012-m (0.046-in) or 2.27% of blade height.

Experimental Study on the Three-Dimensional Flow Within a Compressor Cascade With Tip Clearance: Part II—The Tip Leakage Vortex

1993 ◽  
Vol 115 (3) ◽  
pp. 444-450 ◽  
Author(s):  
S. Kang ◽  
C. Hirsch
Keyword(s):  
Vortex Core ◽  
Three Dimensional ◽  
Leading Edge ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Vortex Center ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Tip Leakage Vortex ◽  
Tip Leakage

An analysis of the experimental data of a linear compressor cascade with tip clearance is presented with special attention to the development of the tip leakage vortex. A method for determining the tip vortex core size, center position, and vorticity or circulation from the measured data is proposed, based on the assumption of a circular tip vortex core. It is observed that the axial velocity profile passing through the tip vortex center is wavelike. The vorticity of the tip vortex increases rapidly near the leading edge and reaches its highest values at a short distance downstream, from which it gradually decreases. In the whole evolution, its size is growing and its center is moving away from both the suction surface and the endwall, approximately in a linear way.

Influence of Blade Tip Surface Roughness On the Performance of a Single Stage Axial Flow Compressor

2021 ◽  
Author(s):  
Pradyumna Kodancha ◽  
Pramod Salunkhe
Keyword(s):  
Surface Roughness ◽  
Axial Flow ◽  
Single Stage ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Axial Flow Compressor ◽  
Blade Tip ◽  
Flow Compressor

Abstract Numerical investigations are carried out in a single-stage subsonic axial flow compressor to unravel the influence of blade tip surface roughness on the tip leakage flow characteristics and hence the compressor performance. The studies were carried out at different tip clearance of 0.38?, 0.77?, 1.15? and 1.54? and blade tip surface roughness of 0.31? and 0.62?. The tip clearance of 0.38? with blade tip surface roughness of 0.62? resulted in the highest stall margin and pressure rise of 20.3% and 4.3%, respectively. The compressor blade loading was found to be improved by 5.9% after incorporating the blade tip surface roughness. The iso-surfaces of vorticity contour plotted using the Q-criterion showed the reduction in strength of the tip leakage vortex. The tip leakage trajectory was found to be shifted towards the suction surface of the blade for the blade tip with surface roughness. This positive alteration in the tip leakage flow structure led to the improved performance for the blade tip with surface roughness.

Time-Averaged Heat Flux for a Recessed Tip, Lip, and Platform of a Transonic Turbine Blade

2000 ◽  
Vol 122 (4) ◽  
pp. 692-698 ◽  
Author(s):  
M. G. Dunn ◽  
C. W. Haldeman
Keyword(s):  
Heat Flux ◽  
Pressure Ratio ◽  
Design Flow ◽  
Turbine Stage ◽  
Suction Surface ◽  
Surface Measurements ◽  
Blade Tip ◽  
Flux Level ◽  
Transonic Turbine ◽  
Exit Mach Number

The results of an experimental research program determining the blade platform heat-flux level and the influence of blade tip recess on the tip region heat transfer for a full-scale rotating turbine stage at transonic vane exit conditions are described. The turbine used for these measurements was the Allison VBI stage operating in the closed vane position (vane exit Mach number≈1.1). The stage was operated at the design flow function, total to static pressure ratio, and corrected speed. Measurements were obtained at several locations on the platform and in the blade tip region. The tip region consists of the bottom of the recess, the lip region (on both the pressure and suction surface sides of the recess), and the 90 percent span location on the blade suction surface. Measurements were obtained for three vane/blade spacings; 20, 40, and 60 percent of vane axial chord and for a single value of the tip gap (the distance between the top of the lip and the stationary shroud) equal to 0.0012 m (0.046 in) or 2.27 percent of blade height. [S0889-504X(00)00604-8]

The Effect of the Casing Movement Relative to the Blades on the Tip Leakage Loss in Axial Flow Compressors

2011 ◽  
Author(s):  
Guillaume Pallot ◽  
Dai Kato ◽  
Hidekazu Kodama ◽  
Kazunari Matsuda ◽  
Hideo Taniguchi ◽  
...  
Keyword(s):  
Axial Flow ◽  
Tip Clearance ◽  
Experimental Results ◽  
Test Facility ◽  
Leakage Loss ◽  
Suction Surface ◽  
Linear Cascade ◽  
High Entropy ◽  
Tip Leakage ◽  
Creation Rate

This paper investigates the effect of the casing movement relative to the blades on the tip leakage loss generation mechanisms by using experimental results from a linear cascade test facility, and viscous numerical results. Traverse measurements in the pitch-wise and span-wise directions are made using a five-hole Pitot tube at the inlet and exit planes of a compressor linear cascade comprising seven equally-pitched blades. The blades are two-dimensionally stacked with a cross section representing a typical rear stage rotor of a highly loaded axial-flow compressor. A moving belt, driven by a motor and a pulley system, runs linearly at constant speed under the horizontally suspended cascade to simulate the relative motion of the blade and the casing. Tip clearance can be adjusted by changing the height of the blades. The experimental results, at 2% and 4% tip clearance to blade heights, indicate that the tip leakage loss decreases when the casing is in movement. The Reynolds-averaged Navier-Stokes numerical calculations with Spalart-Almaras turbulence closure model, run with the experimental boundary conditions, agree well with the test data, especially in terms of dependencies of the leakage loss magnitude on the relative movement between the blade and the casing. It is interesting that, contrary to the tendency in the leakage loss to decrease, the computed tip leakage mass flow rate increases with moving endwall. The computations show two distinct regions of high entropy creation rate near the blade tip. The first one is located close to the blade suction surface where the leakage flow leaves the clearance gap. The second one is located further from the suction surface and the entropy creation rate in this region decreases when the casing is in movement. This paper attempts to provide a qualitative analysis of the flow mechanisms involved in the entropy generation in the second regions. Finally Computations of a high loaded rotor show that the second region identified in the static cascade may also be present in the case of rotating cascades.

scholarly journals Measurements of the Tip Clearance Flow for a High Reynolds Number Axial-Flow Rotor: Part 2 — Detailed Flow Measurements

1994 ◽  
Author(s):  
W. C. Zierke ◽  
K. J. Farrell ◽  
W. A. Straka
Keyword(s):  
Reynolds Number ◽  
Rotor Blade ◽  
High Reynolds Number ◽  
Axial Flow ◽  
Tip Clearance ◽  
Flow Measurements ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Blade Tip ◽  
High Reynolds

A high Reynolds number pump (HIREP) facility has been used to acquire flow measurements in the rotor blade tip clearance region-with blade chord Reynolds numbers of 3,900,000 and 5,500,000. The initial experiment involved rotor blades with varying tip clearances, while a second experiment involved a more detailed investigation of a rotor blade row with a single tip clearance. This paper focuses on detailed flow measurements of the tip leakage vortex. These detailed measurements show the effects of tip clearance size and downstream distance on the structure of the rotor tip leakage vortex. The character of the velocity profile along the vortex core changes from a jet-like profile to a wake-like profile as the tip clearance becomes smaller. These vortex velocity profiles-as well as the levels of unsteadiness-dominate the rotor wake structure in the endwall region. Also, for small clearances, the presence and proximity of the casing endwall affects the roll-up, shape, dissipation, and unsteadiness of the tip leakage vortex. Measurements also show how much circulation is retained by the blade tip and how much is shed into the vortex-a vortex associated with high losses.

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