Comparative Investigation of Three Highly Loaded LP Turbine Airfoils: Part I — Measured Profile and Secondary Losses at Design Incidence

2007 ◽  
Author(s):  
T. Zoric ◽  
I. Popovic ◽  
S. A. Sjolander ◽  
T. Praisner ◽  
E. Grover
Keyword(s):  
Secondary Flow ◽  
Separation Bubble ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Pressure Probe ◽  
Freestream Turbulence ◽  
Wide Range ◽  
Lp Turbine ◽  
Turbine Airfoils ◽  
Highly Loaded

At the 2006 ASME-IGTI Turbo-Expo, low-speed cascade results were presented for the midspan aerodynamic behaviour of a family of three highly loaded low-pressure (LP) turbine airfoils operating over a wide range of Reynolds numbers (25,000 to 150,000 based on the axial chord and inlet velocity), and for values of freestream turbulence intensity of 1.5% and 4%. All three airfoils have the same design inlet and outlet flow angles. The baseline cascade has a Zweifel coefficient of 1.08 and the two additional blade rows have values of 1.37. The new, more highly-loaded blade rows differ mainly in their loading distributions: one is front-loaded while the other is aft-loaded. The new front-loaded airfoil was found to have particularly attractive profile performance. Despite its exceptionally high value of Zweifel coefficient, it was found to be free of a separation bubble on its suction side at Reynolds numbers as low as 50,000, and this was reflected in very good profile loss behaviour. However, it was also noted in the earlier paper that the choice of a particular loading level and loading distribution would be influenced by more than its profile performance at design incidence. The present two-part paper extends the midspan aerodynamic comparison of the three airfoils to the secondary flow performance. The first part of the paper discusses both the profile and secondary flow performance of the three cascades at their design Reynolds number of 80,000 (or ∼ 125,000 based on exit velocity) for two freestream turbulence intensities of 1.5% and 4%. The secondary flow behaviour was determined from detailed flowfield measurements made at 40% axial chord downstream of the trailing edge using a seven-hole pressure probe. In addition to providing total pressure losses, the seven-hole probe measurements were also processed to give the downstream vorticity distributions. As has been found in other secondary flow investigations in turbine cascades, the present front-loaded airfoil showed higher secondary losses than the aft-loaded airfoil with the same value of Zweifel coefficient.

Comparative Investigation of Three Highly Loaded LP Turbine Airfoils: Part II — Measured Profile and Secondary Losses at Off-Design Incidence

2007 ◽  
Author(s):  
T. Zoric ◽  
I. Popovic ◽  
S. A. Sjolander ◽  
T. Praisner ◽  
E. Grover
Keyword(s):  
Separation Bubble ◽  
Suction Side ◽  
Comparative Investigation ◽  
Secondary Flows ◽  
The Other ◽  
Pressure Probe ◽  
Low Pressure Turbine ◽  
Profile Losses ◽  
Lp Turbine ◽  
Turbine Airfoils

The first part of the paper compared the midspan aerodynamics and the secondary flows for a family of three low-pressure turbine (LPT) airfoils at design conditions. However, since a typical engine spends much of its time operating at off-design conditions, good tolerance of LPT airfoils to off-design operation is desired. The sensitivity of the midspan flow to Reynolds number was examined for the three airfoils in a paper presented at the 2006 ASME-IGTI Turbo-Expo. The present paper examines the performance of the airfoils for three values of incidence: −5, 0, and +5 degrees relative to design. Both the profile and secondary losses are considered. Detailed loading distributions measured at midspan are used to explain the behaviour of the profile flow and the resulting change in losses as the incidence was varied. The secondary flow behaviour is determined as at the design incidence from detailed flowfield measurements made downstream of the trailing edge using a seven-hole pressure probe. The results show that in terms of profile losses the baseline airfoil (which has a Zweifel coefficient Z = 1.08) and the front-loaded one with Z = 1.37 have comparable losses over the range of incidences examined. However, the aft-loaded airfoil with Z = 1.37 had noticeably higher profile losses than the other two. On the other hand, the front-loaded one has higher secondary losses than its aft-loaded counterpart at all conditions examined. This obviously poses a dilemma for the designer in terms of the choice of loading distribution. It was also noted that the distribution of loading seems to affect the secondary losses more than the loading level (Zweifel coefficient). An interaction of the secondary flows with the suction side separation bubble might be responsible in part for this finding.

Aerodynamics of a Family of Three Highly Loaded Low-Pressure Turbine Airfoils: Measured Effects of Reynolds Number and Turbulence Intensity in Steady Flow

2006 ◽  
Author(s):  
I. Popovic ◽  
J. Zhu ◽  
W. Dai ◽  
S. A. Sjolander ◽  
T. Praisner ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
Separation Bubble ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Aerodynamic Performance ◽  
Favourable Effect ◽  
Pressure Probe ◽  
Turbine Airfoils

The steady, midspan aerodynamic performance of a family of three low pressure (LP) turbine airfoils has been investigated in a low-speed cascade wind tunnel. The baseline profile has a Zweifel coefficient of 1.08. To examine the influence of increased loading as well as the loading distribution, two additional airfoils were designed, each with 25% higher loading than the baseline version. All three airfoils have the same design inlet and outlet flow angles. The aerodynamic performance was investigated for Reynolds numbers ranging from 25,000 to 150,000 (based on the axial chord and inlet velocity) and for values of freestream turbulence intensity of 1.5% and 4%. The flow field was measured with a three-hole pressure probe. Also, detailed loading distributions were obtained for all three airfoils using surface static pressure taps. The baseline airfoil and the new aft-loaded airfoil showed a separation bubble on the suction side of the airfoil under most of the conditions examined. In addition, a sudden and intermittent stall was observed at low Reynolds numbers for the new aft-loaded airfoil. The relatively short separation bubble would abruptly “burst” and fail to reattach. As the Reynolds number was decreased over a narrow range, the percentage of time that the flow was fully-separated increased to 100%. By comparison, the separation bubble on the baseline airfoil gradually increased in size in an orderly way as the Reynolds number was decreased. The new front-loaded airfoil provided the most encouraging performance: no separation bubble was present except at the very lowest Reynolds numbers. The absence of a separation bubble also had a favourable effect on the loss behaviour of this airfoil: despite its much higher aerodynamic loading, it exhibited very similar midspan losses to those observed for the baseline airfoil.

The Effect of Pulsed Blowing on the Boundary Layer of a Highly Loaded Low Pressure Turbine Blade

2013 ◽  
Author(s):  
Marion Mack ◽  
Roland Brachmanski ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Trailing Edge ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Highly Loaded

The performance of the low pressure turbine (LPT) can vary appreciably, because this component operates under a wide range of Reynolds numbers. At higher Reynolds numbers, mid and aft loaded profiles have the advantage that transition of suction side boundary layer happens further downstream than at front loaded profiles, resulting in lower profile loss. At lower Reynolds numbers, aft loading of the blade can mean that if a suction side separation exists, it may remain open up to the trailing edge. This is especially the case when blade lift is increased via increased pitch to chord ratio. There is a trend in research towards exploring the effect of coupling boundary layer control with highly loaded turbine blades, in order to maximize performance over the full relevant Reynolds number range. In an earlier work, pulsed blowing with fluidic oscillators was shown to be effective in reducing the extent of the separated flow region and to significantly decrease the profile losses caused by separation over a wide range of Reynolds numbers. These experiments were carried out in the High-Speed Cascade Wind Tunnel of the German Federal Armed Forces University Munich, Germany, which allows to capture the effects of pulsed blowing at engine relevant conditions. The assumed control mechanism was the triggering of boundary layer transition by excitation of the Tollmien-Schlichting waves. The current work aims to gain further insight into the effects of pulsed blowing. It investigates the effect of a highly efficient configuration of pulsed blowing at a frequency of 9.5 kHz on the boundary layer at a Reynolds number of 70000 and exit Mach number of 0.6. The boundary layer profiles were measured at five positions between peak Mach number and the trailing edge with hot wire anemometry and pneumatic probes. Experiments were conducted with and without actuation under steady as well as periodically unsteady inflow conditions. The results show the development of the boundary layer and its interaction with incoming wakes. It is shown that pulsed blowing accelerates transition over the separation bubble and drastically reduces the boundary layer thickness.

Predictions of the Effect of Roughness on Heat Transfer From Turbine Airfoils

1998 ◽  
Author(s):  
Anil K. Tolpadi ◽  
Michael E. Crawford
Keyword(s):  
Heat Transfer ◽  
Side Surface ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Surface Finishing ◽  
Transfer Coefficients ◽  
Average Roughness ◽  
Wide Range ◽  
Turbine Airfoils ◽  
Good Agreement

The heat transfer and aerodynamic performance of turbine airfoils are greatly influenced by the gas side surface finish. In order to operate at higher efficiencies and to have reduced cooling requirements, airfoil designs require better surface finishing processes to create smoother surfaces. In this paper, three different cast airfoils were analyzed: the first airfoil was grit blasted and codep coated, the second airfoil was tumbled and aluminide coated, and the third airfoil was polished further. Each of these airfoils had different levels of roughness. The TEXSTAN boundary layer code was used to make predictions of the heat transfer along both the pressure and suction sides of all three airfoils. These predictions have been compared to corresponding heat transfer data reported earlier by Abuaf et al. (1997). The data were obtained over a wide range of Reynolds numbers simulating typical aircraft engine conditions. A three-parameter full-cone based roughness model was implemented in TEXSTAN and used for the predictions. The three parameters were the centerline average roughness, the cone height and the cone-to-cone pitch. The heat transfer coefficient predictions indicated good agreement with the data over most Reynolds numbers and for all airfoils-both pressure and suction sides. The transition location on the pressure side was well predicted for all airfoils; on the suction side, transition was well predicted at the higher Reynolds numbers but was computed to be somewhat early at the lower Reynolds numbers. Also, at lower Reynolds numbers, the heat transfer coefficients were not in very good agreement with the data on the suction side.

Experiments With Three-Dimensional Passive Flow Control Devices on Low-Pressure Turbine Airfoils

2004 ◽  
Vol 128 (2) ◽  
pp. 251-260 ◽  
Author(s):  
Douglas G. Bohl ◽  
Ralph J. Volino
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Trailing Edge ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Turbine Airfoils

The effectiveness of three-dimensional passive devices for flow control on low pressure turbine airfoils was investigated experimentally. A row of small cylinders was placed at the pressure minimum on the suction side of a typical airfoil. Cases with Reynolds numbers ranging from 25,000 to 300,000 (based on suction surface length and exit velocity) were considered under low freestream turbulence conditions. Streamwise pressure profiles and velocity profiles near the trailing edge were documented. Without flow control a separation bubble was present, and at the lower Reynolds numbers the bubble did not close. Cylinders with two different heights and a wide range of spanwise spacings were considered. Reattachment moved upstream as the cylinder height was increased or the spacing was decreased. If the spanwise spacing was sufficiently small, the flow at the trailing edge was essentially uniform across the span. The cylinder size and spacing could be optimized to minimize losses at a given Reynolds number, but cylinders optimized for low Reynolds number conditions caused increased losses at high Reynolds numbers. The effectiveness of two-dimensional bars had been studied previously under the same flow conditions. The cylinders were not as effective for maintaining low losses over a range of Reynolds numbers as the bars.

Active Flow Control Concepts on a Highly Loaded Subsonic Compressor Cascade: Résumé of Experimental and Numerical Results

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Christoph Gmelin ◽  
Vincent Zander ◽  
Martin Hecklau ◽  
Frank Thiele ◽  
Wolfgang Nitsche ◽  
...  
Keyword(s):  
Flow Control ◽  
Active Flow Control ◽  
Suction Side ◽  
Numerical Results ◽  
Pressure Probe ◽  
Control Parameters ◽  
Compressor Cascade ◽  
Wide Range ◽  
Active Flow ◽  
Highly Loaded

This paper presents experimental and numerical results for a highly loaded, low speed, linear compressor cascade with active flow control. Three active flow control concepts employing steady jets, pulsed jets, and zero mass flow jets (synthetic jets) are investigated at two different forcing locations: at the end walls and the blade suction side. Investigations are performed at the design incidence for jet-to-inlet velocity ratios of approximately 0.7 to 3.0 and two different Reynolds numbers. Detailed flow field data are collected using a five-hole pressure probe, pressure tabs on the blade surfaces, and time-resolved particle image velocimetry. Unsteady Reynolds-Averaged Navier-Stokes simulations are performed for a wide range of flow control parameters. The experimental and numerical results are used to understand the interaction between the jet and the passage flow. Variation of jet amplitude, forcing frequency and blowing angle of the different control concepts at both locations allows determination of beneficial control parameters and offers a comparison between similar control approaches. This paper combines the advantages of an expensive yet reliable experiment and a fast but limited numerical simulation. Excellent agreement in control effectiveness is found between experiment and simulation.

Experiments With Three Dimensional Passive Flow Control Devices on Low-Pressure Turbine Airfoils

2005 ◽  
Author(s):  
Douglas G. Bohl ◽  
Ralph J. Volino
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Trailing Edge ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Turbine Airfoils

The effectiveness of three dimensional passive devices for flow control on low pressure turbine airfoils was investigated experimentally. A row of small cylinders was placed at the pressure minimum on the suction side of a typical airfoil. Cases with Reynolds numbers ranging from 25,000 to 300,000 (based on suction surface length and exit velocity) were considered under low freestream turbulence conditions. Streamwise pressure profiles and velocity profiles near the trailing edge were documented. Without flow control a separation bubble was present, and at the lower Reynolds numbers the bubble did not close. Cylinders with two different heights and a wide range of spanwise spacings were considered. Reattachment moved upstream as the cylinder height was increased or the spacing was decreased. If the spanwise spacing was sufficiently small, the flow at the trailing edge was essentially uniform across the span. The cylinder size and spacing could be optimized to minimize losses at a given Reynolds number, but cylinders optimized for low Reynolds number conditions caused increased losses at high Reynolds numbers. The effectiveness of two-dimensional bars had been studied previously under the same flow conditions. The cylinders were not as effective for maintaining low losses over a range of Reynolds numbers as the bars.

A Novel Method for Improvement of Aerodynamic Performance of Highly Loaded LP Turbine Airfoils for Aeroengines

2013 ◽  
Author(s):  
K. Funazaki ◽  
K. Okamura ◽  
Y. Ebina ◽  
Y. Sato ◽  
T. Kosugi ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Aerodynamic Performance ◽  
Test Facility ◽  
Surface Boundary ◽  
Suction Surface ◽  
Wide Range ◽  
Novel Method ◽  
Lp Turbine ◽  
Turbine Airfoils ◽  
Highly Loaded

This paper proposes a novel method to improve aerodynamic performance of highly loaded Low-Pressure (LP) turbine airfoils for aeroengines over a relatively wide range of Reynolds number. This new method employs two types of approaches; one is the equipment of two-dimensional contouring with small step on the suction surface of the airfoil and the other approach is a re-shaping of the airfoil near the trailing edge. A linear cascade test facility is employed to investigate the aerodynamic performance of the newly proposed airfoils by use of a miniature Pitot probe. Suction surface boundary layers as well as airfoil wakes are also measured using a hot wire probe. In the experiment, various flow conditions, Reynolds number, wake-passing Strouhal number, are examined. Numerical simulations are carried out to have a better understanding of the flow field around the airfoil. URANS and LES are employed for this purpose. It is found that the proposed method has a capability to reduce the profile loss to some extent.

Investigation of a Separated Boundary Layer and its Influence on Secondary Flow of a Transonic Turbine Profile

2014 ◽  
Author(s):  
Roland E. Brachmanski ◽  
Reinhard Niehuis ◽  
Arianna Bosco
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Turbine Blade ◽  
Flow Separation ◽  
High Speed ◽  
Separation Bubble ◽  
Armed Forces ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Operation Conditions

Profile losses of the turbine blade and secondary flow losses are the main source of aerodynamic loss in a low pressure turbine. However, not much attention has been paid in the interaction between these two loss sources. This paper investigates the interaction mechanisms between a separated boundary layer on the suction side and the secondary flow in blade passages. The high speed cascade wind tunnel of the University of the Federal Armed Forces Germany has been used to achieve the required operation conditions, generating a flow separation on the suction side. The profile of this cascade has been chosen due to the flow separation behavior on the suction side of the blade at low Reynolds numbers. Different measurements techniques are conducted to further investigate the effects seen in CFD. The aim of this paper is to investigate the interaction phenomena between the secondary flow and a separation bubble at different Reynolds numbers. The development and change of the boundary layer in the axial and radial directions on the suction side of the turbine blade are presented and discussed. The results show discrepancies between the numerical prediction and the experimental data on the suction side of the blade rise as the effects of the secondary flow increase. Furthermore, the increasing influence of the radial pressure gradient of the secondary flow leads to a noticeable reduction in the length of the separation bubble close to the endwall region.

The Influence of Technical Surface Roughness on the Flow Around a Highly Loaded Compressor Cascade

1999 ◽  
Author(s):  
Robert Leipold ◽  
Matthias Boese ◽  
Leonhard Fottner
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Pressure Distribution ◽  
Total Pressure ◽  
Separation Bubble ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Flow Conditions ◽  
Compressor Cascade ◽  
Highly Loaded

A highly loaded compressor cascade which features a chord length that is ten times larger than in real turbomachinary is used to perform an investigation of the influence of technical surface roughness. The surface structure of a precision forged blade was engraved in two 0.3mm thick sheets of copper with the above mentioned enlarging factor (Leipold and Fottner, 1998). To avoid additional effects due to thickening of the blade contour the sheets of copper are applied as inlay’s to the pressure and suction side. At the high speed cascade wind tunnel the profile pressure distribution and the total pressure distribution at the exit measurement plane were measured for the rough and the smooth blade for a variation of inlet flow angle and inlet Reynolds number. For some interesting flow conditions the boundary layer development was investigated with the laser-two-focus anemometry and the one-dimensional hot-wire anemometry. At low Reynolds numbers and small inlet angles a separation bubble is only slightly reduced due to surface roughness. The positive effect of a reduced separation bubble is overcompensated by a negative influence of surface roughness on the turbulent boundary layer downstream of the separation bubble. At high Reynolds numbers the flow over the rough blade shows a turbulent separation leading to high total pressure loss coefficients. The laser-two-focus measurements indicate a velocity deficit close to the trailing edge even at flow conditions where positive effects due to a reduction of the suction side separation have been expected. The turbulence intensity is reduced close downstream of the separation bubble but increased further downstream due to surface roughness. Thus not the front part but the rear part of the blade reacts sensitively on surface roughness.

Sign in / Sign up

Export Citation Format

Share Document