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 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.

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 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 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.

scholarly journals Aerodynamic Losses in Turbines with and without Film Cooling, as Influenced by Mainstream Turbulence, Surface Roughness, Airfoil Shape, and Mach Number

2012 ◽  
Vol 2012 ◽  
pp. 1-28 ◽  
Author(s):  
Phil Ligrani
Keyword(s):  
Surface Roughness ◽  
Mach Number ◽  
Film Cooling ◽  
Total Pressure ◽  
High Speed ◽  
Density Ratio ◽  
Aerodynamic Loss ◽  
Pressure Losses ◽  
Loss Coefficients ◽  
Exit Mach Number

The influences of a variety of different physical phenomena are described as they affect the aerodynamic performance of turbine airfoils in compressible, high-speed flows with either subsonic or transonic Mach number distributions. The presented experimental and numerically predicted results are from a series of investigations which have taken place over the past 32 years. Considered are (i) symmetric airfoils with no film cooling, (ii) symmetric airfoils with film cooling, (iii) cambered vanes with no film cooling, and (iv) cambered vanes with film cooling. When no film cooling is employed on the symmetric airfoils and cambered vanes, experimentally measured and numerically predicted variations of freestream turbulence intensity, surface roughness, exit Mach number, and airfoil camber are considered as they influence local and integrated total pressure losses, deficits of local kinetic energy, Mach number deficits, area-averaged loss coefficients, mass-averaged total pressure loss coefficients, omega loss coefficients, second law loss parameters, and distributions of integrated aerodynamic loss. Similar quantities are measured, and similar parameters are considered when film-cooling is employed on airfoil suction surfaces, along with film cooling density ratio, blowing ratio, Mach number ratio, hole orientation, hole shape, and number of rows of holes.

scholarly journals The Effect of Surface Roughness on Diffusion and Chemical Reaction Controlled Limiting Currents on a Rotating Cylinder Electrode in Deaerated Solutions with and Without CO2

CORROSION ◽  
10.5006/2552 ◽  
2018 ◽  
Vol 74 (9) ◽  
pp. 971-983 ◽  
Author(s):  
M. Al-Khateeb ◽  
R. Barker ◽  
A. Neville ◽  
H.M. Thompson
Keyword(s):  
Mass Transfer ◽  
Surface Roughness ◽  
Sherwood Number ◽  
Schmidt Number ◽  
Rotating Cylinder ◽  
Operating Conditions ◽  
Limiting Current ◽  
Surface Roughening ◽  
Rotating Cylinder Electrode ◽  
Effect Of Surface

The influence of surface roughness on mass transfer on a rotating cylinder electrode apparatus is investigated experimentally for a roughness pattern consisting of grooves parallel to the direction of fluid flow. Mass transfer from four different samples, with roughness values of 0.5 μm, 6 μm, 20 μm, and 34 μm, is measured using the limiting current technique for a range of rotational speeds in NaCl solutions saturated with N2 at pH = 3 and 4. Comparison with available correlations for the Sherwood number in literature (which are independent of surface roughness and are either for specific or arbitrary roughness patterns) shows that H+ mass transfer only correlates well for particular levels of roughness and that their accuracy can be increased if a correlation is utilized which is a function of surface roughening. A new correlation for Sherwood number as a function of the Reynolds number, Schmidt number, and surface roughness is proposed which agrees well with the mass transfer observed from all of the rough surface cases considered for this particular roughness pattern. Complementary experiments in CO2 environments were used to assess the combined limiting current associated with H+ and H2CO3 reduction (with the latter occurring via the buffering effect and being associated with the slow CO2 hydration step). Although the increase in sample roughness clearly leads to an increase in the rate of H+ mass transfer, in the CO2 environments considered, surface roughness is found to have no significant influence on the limiting current contribution from H2CO3, which can therefore be determined from Vetter’s equation across this range of operating conditions.

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.

A Comparison of Turbulence Levels From Particle Image Velocimetry and Constant Temperature Anemometry Downstream of a Low-Pressure Turbine Cascade at High-Speed Flow Conditions

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
Silvio Chemnitz ◽  
Reinhard Niehuis
Keyword(s):  
Particle Image Velocimetry ◽  
Constant Temperature ◽  
High Speed ◽  
Particle Image ◽  
Low Pressure ◽  
Operating Conditions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Turbine Cascade ◽  
Low Pressure Turbine ◽  
Image Velocimetry

Abstract The development and verification of new turbulence models for Reynolds-averaged Navier–Stokes (RANS) equation-based numerical methods require reliable experimental data with a deep understanding of the underlying turbulence mechanisms. High accurate turbulence measurements are normally limited to simplified test cases under optimal experimental conditions. This work presents comprehensive three-dimensional data of turbulent flow quantities, comparing advanced constant temperature anemometry (CTA) and stereoscopic particle image velocimetry (PIV) methods under realistic test conditions. The experiments are conducted downstream of a linear, low-pressure turbine cascade at engine relevant high-speed operating conditions. The special combination of high subsonic Mach and low Reynolds number results in a low density test environment, challenging for all applied measurement techniques. Detailed discussions about influences affecting the measured result for each specific measuring technique are given. The presented time mean fields as well as total turbulence data demonstrate with an average deviation of ΔTu<0.4% and ΔC/Cref<0.9% an extraordinary good agreement between the results from the triple sensor hot-wire probe and the 2D3C-PIV setup. Most differences between PIV and CTA can be explained by the finite probe size and individual geometry.

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