The Effect of Airfoil Thickness on the Efficiency of LP Turbines

2012 ◽  
Author(s):  
Diego Torre ◽  
Raúl Vázquez ◽  
Leyre Armanañzas ◽  
Fernando Partida ◽  
Guillermo García-Valdecasas
Keyword(s):  
High Speed ◽  
Separation Bubble ◽  
Pressure Coefficient ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Specific Work ◽  
Suction Surface ◽  
Small Areas ◽  
The Impact ◽  
Very High

The effect of airfoil thickness on the efficiency of Low Pressure (LP) Turbines has been investigated experimentally in a multistage turbine high-speed rig. The rig consists of three stages of a state of the art LP turbine. The stages are characterized by a very high hade angle, reverse cut-off design, very high lift and very high aspect ratio airfoils. Two different sets of stators have been designed and tested. The first set of stators is made of airfoils with a thickness to chord ratio around 10% along the span with exception of a small areas close to the endwalls. In those areas, the thickness has been increased above the previous value to reduce the secondary flows. These types of airfoils have been referred in the literature as “spoon” airfoils. The second set of stators has been designed to have the same spanwise distribution of pressure coefficient (Cp) on the suction surface than the first set. However, the thickness to chord ratio was increased along the span up to values around 20% to rise the velocity of the flow and to remove any separation bubble on the pressure side. The resulting shape of the profiles is representative of “hollow” airfoils. The velocity triangles, chord distribution, leading and trailing edge locations and flowpath have been maintained between both sets. They have been tested with the same blades and at the same operating conditions with the intention of determining the impact of the profile thickness on the overall efficiency. The turbine characteristics: sensitivity to speed, specific work, Reynolds number and purge flows have been obtained for both sets. The comparison of the results suggests that the efficiency of both types of airfoils exhibit the same behaviour, no significant differences in the results can be distinguished.

The Effect of Airfoil Thickness on the Efficiency of Low-Pressure Turbines

2013 ◽  
Vol 136 (5) ◽  
Author(s):  
Diego Torre ◽  
Raúl Vázquez ◽  
Leyre Armañanzas ◽  
Fernando Partida ◽  
Guillermo García-Valdecasas
Keyword(s):  
High Speed ◽  
Separation Bubble ◽  
Pressure Coefficient ◽  
Low Pressure ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Specific Work ◽  
Suction Surface ◽  
The Impact ◽  
Very High

The effect of airfoil thickness on the efficiency of low-pressure (LP) turbines has been investigated experimentally in a multistage turbine high-speed rig. The rig consists of three stages of a state of the art LP turbine. The stages are characterized by a very high hade angle, reverse cut-off design, very high lift, and very high aspect ratio airfoils. Two different sets of stators have been designed and tested. The first set of stators is made of airfoils with a thickness to chord ratio around 10% along the span with the exception of a small areas close to the end walls. In those areas, the thickness has been increased above the previous value to reduce the secondary flows. These types of airfoils have been referred to in the literature as “spoon” airfoils. The second set of stators has been designed to have the same spanwise distribution of pressure coefficient (Cp) on the suction surface than the first set. However, the thickness to chord ratio was increased along the span up to values around 20% to raise the velocity of the flow and to remove any separation bubble on the pressure side. The resulting shape of the profiles is representative of “hollow” airfoils. The velocity triangles, chord distribution, leading and trailing edge locations, and flowpath have been maintained between both sets. They have been tested with the same blades and at the same operating conditions with the intention of determining the impact of the profile thickness on the overall efficiency. The turbine characteristics: sensitivity to speed, specific work, Reynolds number, and purge flows have been obtained for both sets. The comparison of the results suggests that the efficiency of both types of airfoils exhibit the same behavior; no significant differences in the results can be distinguished.

The Effect of Surface Roughness on Efficiency of Low Pressure Turbines

2013 ◽  
Vol 136 (6) ◽  
Author(s):  
Raúl Vázquez ◽  
Diego Torre
Keyword(s):  
Surface Roughness ◽  
High Speed ◽  
Slope Angle ◽  
Low Pressure ◽  
Operating Conditions ◽  
Specific Work ◽  
Pressure Losses ◽  
Comparison Of The Results ◽  
Very High ◽  
Effect Of Surface

The effect of surface roughness on the efficiency of low pressure turbines (LPTs) was experimentally investigated in a multistage turbine high-speed rig. The rig consisted of three stages of a state-of-the-art LPT. The stages were characterized by a very high wall-slope angle, reverse cut-off design, very high lift, and very high aspect ratio airfoils. Two sets of airfoils (both stators and rotors) were tested. The first set was made of airfoils with a roughness size of 0.7 μm Ra (25–35 × 10−5 ks/Cm), which was representative of LPT polished airfoils. The surface finish for the second set of airfoils was 1.8 μm Ra for blades and 2.5 μm Ra for stators (approximately 90 × 10−5 in terms of ks/Cm for both stators and blades). The resulting roughness of this set was representative of “as-cast” airfoils of low pressure turbines. The airfoil geometries, velocity triangles, leading and trailing edge locations, and flowpath were maintained between both sets. They were tested with the same instrumentation and at the same operating conditions with the intention of determining the isolated impact of the surface roughness on the overall efficiency. The turbine characteristics: sensitivity to speed, specific work, Reynolds number, and purge flows, were obtained for both sets. The comparison of the results suggests that the efficiency and capacity of both types of airfoils exhibit the same behavior. No significant differences in the results can be distinguished for the range of operating conditions in this study. The results agree with previous studies of distributed roughness in turbines: the use of as-cast rough airfoils in some low pressure turbines at high altitude does not introduce additional pressure losses.

The Effect of Airfoil Clocking on Efficiency and Noise of Low Pressure Turbines

2013 ◽  
Author(s):  
Raúl Vázquez ◽  
Diego Torre ◽  
Adolfo Serrano
Keyword(s):  
High Speed ◽  
Slope Angle ◽  
Low Pressure ◽  
Operating Conditions ◽  
Airfoil Surface ◽  
Multistage Turbine ◽  
Overall Efficiency ◽  
Comparison Of The Results ◽  
The Impact ◽  
Very High

The effect of airfoil clocking (stator-stator interaction) on efficiency and noise of low pressure turbines (LPT) was investigated experimentally in a multistage turbine high-speed rig. The rig consisted of three stages of a state-of-the-art LPT. The stages were characterized by a very high wall-slope angle, reverse cut-off design, very high lift and very high aspect ratio airfoils. The rig had identical blade count for the second and third stators. The circumferential position of the second stator was individually adjusted with respect to the third stator. Eight different circumferential clocking locations over one pitch were back-to-back tested. The rig was heavily instrumented with miniature five hole probes, hot wires, hot films, total pressure and temperature rakes, pressure tappings on the airfoil surface, two array of Kulites in a rotatory module, etc. Every clocking location was tested with the same instrumentation and at the same operating conditions with the intention of determining the impact of the clocking on the overall efficiency and noise. Due to the large amount of data, the results of this test will be reported in several papers. The present paper contains the impact on the overall efficiency, radial traverses, static pressure fields on the airfoils and averaged sound pressure levels in the duct. The comparison of the results suggests that the efficiency is weakly affected by clocking; however the effect on noise is noticeable for some acoustic tones at certain operating conditions.

The Effect of Airfoil Clocking on Efficiency and Noise of Low Pressure Turbines

2013 ◽  
Vol 136 (6) ◽  
Author(s):  
Raúl Vázquez ◽  
Diego Torre ◽  
Adolfo Serrano
Keyword(s):  
High Speed ◽  
Slope Angle ◽  
Low Pressure ◽  
Operating Conditions ◽  
Airfoil Surface ◽  
Multistage Turbine ◽  
Overall Efficiency ◽  
Comparison Of The Results ◽  
The Impact ◽  
Very High

The effect of airfoil clocking (stator-stator interaction) on efficiency and noise of low pressure turbines (LPT) was investigated experimentally in a multistage turbine high-speed rig. The rig consisted of three stages of a state-of-the-art LPT. The stages were characterized by a very high wall-slope angle, reverse cut-off design, very high lift, and very high aspect ratio airfoils. The rig had identical blade count for the second and third stators. The circumferential position of the second stator was individually adjusted with respect to the third stator. Eight different circumferential clocking locations over one pitch were back-to-back tested. The rig was heavily instrumented with miniature five hole probes, hot wires, hot films, total pressure and temperature rakes, pressure tappings on the airfoil surface, two array of Kulites in a rotatory module, etc. Every clocking location was tested with the same instrumentation and at the same operating conditions with the intention of determining the impact of the clocking on the overall efficiency and noise. Due to the large amount of data, the results of this test will be reported in several papers. The present paper contains the impact on the overall efficiency, radial traverses, static pressure fields on the airfoils and averaged sound pressure levels in the duct. The comparison of the results suggests that the efficiency is weakly affected by clocking; however the effect on noise is noticeable for some acoustic tones at certain operating conditions.

The Effect of Surface Roughness on Efficiency of Low Pressure Turbines

2013 ◽  
Author(s):  
Raúl Vázquez ◽  
Diego Torre
Keyword(s):  
Surface Roughness ◽  
High Speed ◽  
Slope Angle ◽  
Low Pressure ◽  
Operating Conditions ◽  
Specific Work ◽  
Pressure Losses ◽  
Comparison Of The Results ◽  
Very High ◽  
Effect Of Surface

The effect of surface roughness on efficiency of low pressure turbines (LPT) was investigated experimentally in a multistage turbine high-speed rig. The rig consisted of three stages of a state-of-the-art LPT. The stages were characterized by a very high wall-slope angle, reverse cut-off design, very high lift and very high aspect ratio airfoils. Two sets of airfoils (both stators and rotors) were tested. The first set was made of airfoils with a roughness size of 0.7 μm Ra (25–35×10−5 ks/Cm), which was representative of LPT polished airfoils. The surface finish for the second set of airfoils was 1.8 μm Ra for blades and 2.5 μm Ra for stators (approximately 90×10−5 in terms of ks/Cm for both stators and blades). The resulting roughness of this set was representative of “as-cast” airfoils of low pressure turbines. The airfoil geometries, velocity triangles, leading and trailing edge locations and flowpath were maintained between both sets. They were tested with the same instrumentation and at the same operating conditions with the intention of determining the isolated impact of the surface roughness on the overall efficiency. The turbine characteristics: sensitivity to speed, specific work, Reynolds number and purge flows were obtained for both sets. The comparison of the results suggests that the efficiency and capacity of both types of airfoils exhibit the same behaviour. No significant differences in the results can be distinguished for the range of operating conditions of this study. The results agree with previous studies of distributed roughness in turbines: the use of as-cast rough airfoils in some low pressure turbines at high altitude does not introduce additional pressure losses.

Direct Outer Ring Cooling of a High Speed Jet Engine Mainshaft Ball Bearing: Experimental Investigation Results

2010 ◽  
Author(s):  
Peter Gloeckner ◽  
Klaus Dullenkopf ◽  
Michael Flouros
Keyword(s):  
Power Dissipation ◽  
High Speed ◽  
Ball Bearing ◽  
Operating Conditions ◽  
Outer Ring ◽  
Outer Diameter ◽  
Propulsion Systems ◽  
Jet Engine ◽  
Power Loss Reduction ◽  
The Impact

Operating conditions in high speed mainshaft ball bearings applied in new aircraft propulsion systems require enhanced bearing designs and materials. Rotational speeds, loads, demands on higher thrust capability, and reliability have increased continuously over the last years. A consequence of these increasing operating conditions are increased bearing temperatures. A state of the art jet engine high speed ball bearing has been modified with an oil channel in the outer diameter of the bearing. This oil channel provides direct cooling of the outer ring. Rig testing under typical flight conditions has been performed to investigate the cooling efficiency of the outer ring oil channel. In this paper the experimental results including bearing temperature distribution, power dissipation, bearing oil pumping and the impact on oil mass and parasitic power loss reduction are presented.

Correlations Hidden in Compressor Maps

2011 ◽  
Author(s):  
Joachim Kurzke
Keyword(s):  
High Speed ◽  
Pressure Ratio ◽  
Leading Edge ◽  
Operating Conditions ◽  
Specific Work ◽  
Gas Generator ◽  
High Pressure Ratio ◽  
Map Adaptation ◽  
Physical Phenomena ◽  
Corrected Flow

Realistic compressor maps are the key to high quality gas turbine performance calculations. When modeling the performance of an existing engine then these maps are usually not known and must be approximated by adapting maps from literature to either measured data or to other available information. There are many publications describing map adaptation processes, simple ones and more sophisticated physically based scaling rules. There are also reports about using statistics, genetic algorithms, neural networks and even morphing techniques for re-engineering compressor maps. This type of methods does not consider the laws of physics and consequently the generated maps are valid at best in the region in which they have been calibrated. This region is frequently very narrow, especially in case of gas generator compressors which run in steady state always on a single operating line. This paper describes which physical phenomena influence the shape of speed and efficiency lines in compressor maps. For machines operating at comparatively low speeds (so that the flow into each stage is subsonic), there is usually considerable range between choke and stall corrected flow. As the speed of the machine is increased the range narrows. For high-speed stages with supersonic relative flow into the rotor the efficiency maximum is where the speed line turns over from vertical to lower than maximum corrected flow. At this operating condition the shock is about to detach from the leading edge of the blades. The flow at a certain speed can also be limited by choking in the compressor exit guide vanes. For high pressure ratio single stage centrifugal compressors this is a normal case, but it can also happen with low pressure ratio multistage boosters of turbofan engines, for example. If the compressor chokes at the exit, then the specific work remains constant along the speed line while the overall pressure ratio varies and that generates a very specific shape of the efficiency contour lines in the map. Also in other parts of the map, the efficiency varies along speed lines in a systematic manner. Peculiar shapes of specific work and corrected torque lines can reveal physically impossibilities that are difficult to see in the standard compressor map pictures. Compressor maps generated without considering the inherent physical phenomena can easily result in misleading performance calculations if used at operating conditions outside of the region where they have been calibrated. Whatever map adaptation method is used: the maps created in such a way should be checked thoroughly for violations of the underlying laws of compressor physics.

Impact of Impeller Casing Treatment on the Acoustics of a Small High Speed Centrifugal Compressor

2018 ◽  
Author(s):  
Sidharath Sharma ◽  
Jorge García-Tíscar ◽  
John M. Allport ◽  
Martyn L. Jupp ◽  
Ambrose K. Nickson
Keyword(s):  
Centrifugal Compressor ◽  
High Speed ◽  
Pressure Fluctuations ◽  
Operating Conditions ◽  
Aerodynamic Noise ◽  
Noise Sources ◽  
Casing Treatment ◽  
Active Research ◽  
Ported Shroud ◽  
The Impact

Ported shroud casing treatment is widely used to delay the onset of surge and thereby enhancing the aerodynamic stability of a centrifugal compressor by recirculating the low momentum fluid in the blade passage. Performance losses associated with the use of recirculation casing treatment are well established in the literature and this is an area of active research. The other, less researched aspect of the casing treatment is its impact on the acoustics of the compressor. This work investigates the impact of ported shroud casing treatment on the acoustic characteristics of the compressor. The flow in two compressor configurations viz. with and without casing treatment operating at the design operating conditions of an iso-speed line are numerically modelled and validated with experimental data from gas stand measurements. The pressure fluctuations calculated as the flow solution are used to compute the spectral signatures at multiple locations to investigate the acoustic phenomenon associated with each configuration. Propagation of the frequency content through the ducts has been estimated with the aid of method of characteristics to enhance the content coming from the compressor. Expected tonal aerodynamic noise sources such as monopole (buzz-saw tones) and dipole (Blade Pass Frequency) are clearly identified in the acoustic spectra of the two configurations. The comparison of two configurations shows higher overall levels and tonal content in the case of a compressor with ported shroud operating at design conditions due to the presence of ‘mid-tones’.

Reliable and Accurate Prediction of Three-Dimensional Separation in Asymmetric Diffusers Using Large-Eddy Simulation

2009 ◽  
Author(s):  
Hayder Schneider ◽  
Dominic von Terzi ◽  
Hans-Jo¨rg Bauer ◽  
Wolfgang Rodi
Keyword(s):  
Experimental Data ◽  
Reverse Flow ◽  
Separation Bubble ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Impact

Reynolds-Averaged Navier-Stokes (RANS) calculations and Large-Eddy Simulations (LES) of the flow in two asymmetric three-dimensional diffusers were performed. The numerical setup was chosen to be in compliance with previous experiments. The aim of the present study is to find the least expensive method to compute reliably and accurately the impact of geometric sensitivity on the flow. RANS calculations fail to predict both the extent and location of the three-dimensional separation bubble. In contrast, LES is able to determine the amount of reverse flow and the pressure coefficient within the accuracy of experimental data.

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