The Experts below are selected from a list of 183 Experts worldwide ranked by ideXlab platform
E A Mayda - One of the best experts on this subject based on the ideXlab platform.
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Flatback airfoil wind tunnel experiment.
2008Co-Authors: E A Mayda, C. P. Van Dam, David D. Chao, Dale E. BergAbstract:A computational fluid dynamics study of thick wind turbine section shapes in the test section of the UC Davis wind tunnel at a chord Reynolds number of one million is presented. The goals of this study are to validate standard wind tunnel wall corrections for high solid blockage conditions and to reaffirm the favorable effect of a blunt trailing edge or flatback on the performance characteristics of a representative thick airfoil shape prior to building the wind tunnel models and conducting the experiment. The numerical simulations prove the standard wind tunnel corrections to be largely valid for the proposed test of 40% maximum thickness to chord Ratio airfoils at a solid blockage Ratio of 10%. Comparison of the computed lift characteristics of a sharp trailing edge baseline airfoil and derived flatback airfoils reaffirms the earlier observed trend of reduced sensitivity to surface contamination with increasing trailing edge thickness.
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Computational Design and Analysis of Flatback Airfoil Wind Tunnel Experiment
2008Co-Authors: E A Mayda, C. P. Van Dam, David D. Chao, Dale E. BergAbstract:A computational fluid dynamics study of thick wind turbine section shapes in the test section of the UC Davis wind tunnel at a chord Reynolds number of one million is presented. The goals of this study are to validate standard wind tunnel wall corrections for high solid blockage conditions and to reaffirm the favorable effect of a blunt trailing edge or flatback on the performance characteristics of a representative thick airfoil shape prior to building the wind tunnel models and conducting the experiment. The numerical simulations prove the standard wind tunnel corrections to be largely valid for the proposed test of 40% maximum thickness to chord Ratio airfoils at a solid blockage Ratio of 10%. Comparison of the computed lift characteristics of a sharp trailing edge baseline airfoil and derived flatback airfoils reaffirms the earlier observed trend of reduced sensitivity to surface contamination with increasing trailing edge thickness.
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experimental analysis of thick blunt trailing edge wind turbine airfoils
Journal of Solar Energy Engineering-transactions of The Asme, 2006Co-Authors: Jonathon P Baker, E A MaydaAbstract:An experimental investigation of blunt trailing-edge orflatback airfoils was conducted in the University of California, Davis aeronautical wind tunnel. The blunt trailing-edge airfoil is created by symmetrically adding thickness to both sides of the camber line of the FB-3500 airfoil, while maintaining the maximum Thickness-to-Chord Ratio of 35%. Three airfoils of various trailing-edge thicknesses (0.5%, 8.75%, and 17.5% chord) are discussed in this paper. In the present study, each airfoil was tested under free and fixed boundary layer transition flow conditions at Reynolds numbers of 333,000 and 666,000. The fixed transition conditions were used to simulate surface soiling effects by placing artificial tripping devices at 2% chord on the suction surface and 5% chord on the pressure surface of each airfoil. The results of this investigation show that lift increases and the well-documented thick airfoil sensitivity to leading-edge transition reduces with increasing trailing-edge thickness. The flatback airfoils yield increased drag coefficients over the sharp trailing-edge airfoil due to an increase in base drag. The experimental results are compared against numerical predictions obtained with two different computational aerodynamics methods. Computations at bounded and unbounded conditions are used to quantify the wind tunnel wall corrections for the wind tunnel tests.
Christian Oliver Paschereit - One of the best experts on this subject based on the ideXlab platform.
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Aerodynamic investigation of guide vane configuRations downstream a rotating detonation combustor
Journal of Engineering for Gas Turbines and Power, 2020Co-Authors: Majid Asli, Panagiotis Stathopoulos, Christian Oliver PaschereitAbstract:Any outlet restriction downstream of Pressure Gain Combustion (PGC), such as turbine blades, affects its flow field and may cause additional thermodynamic losses. The unsteadiness in the form of pressure, temperature and velocity vector fluctuations has a negative impact on the opeRation of conventional turbines. Additionally, experimental measurements and data acquisition present researchers with challenges that have to do mostly with the high temperature exhaust of PGC and the high frequency of its opeRation. Nevertheless, numerical simulations can provide important insights into PGC exhaust flow and its interaction with turbine blades. In this paper, a Rotating Detonation Combustor (RDC) and a row of nozzle guide vanes have been modeled based on the data from literature and an available experimental setup. URANS simulations were done for five guide vane configuRations with different geometrical parameters to investigate the effect of solidity and blade type representing different outlet restrictions on the RDC exhaust flow. The results analyzed the connection between total pressure loss and the vanes solidity and thickness to chord Ratio. It is observed that more than 57% of the upstream velocity angle fluctuation amplitude was damped by the vanes. Furthermore, the area reduction was found to be the significant driving factor for damping the velocity angle fluctuations, whether in the form of solidity or thickness on chord Ratio increment. This RDC exhaust flow investigation is an important primary step from a turbomachinery standpoint, which provided details of blade behavior in such an unsteady flow field.
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Aerodynamic Investigation of Guide Vane ConfiguRations Downstream a Rotating Detonation Combustor
Volume 4B: Combustion Fuels and Emissions, 2020Co-Authors: Majid Asli, Panagiotis Stathopoulos, Christian Oliver PaschereitAbstract:Abstract Pressure Gain Combustion (PGC) is considered a possible solution to increase gas turbine cycle efficiency, due to the lower entropy geneRation in the combustion process. However, the highly unsteady flow produced by PGC makes it more difficult to extract work from its exhaust gas. Any outlet restriction downstream of PGC, such as turbine blades, affects its flow field and may cause additional thermodynamic losses. The unsteadiness in the form of pressure, temperature and velocity vector fluctuations has a negative impact on the opeRation of conventional turbines. Therefore, evaluating early turbine design parameters for such applications is of great interest. Additionally, experimental measurements and data acquisition present researchers with challenges that have to do mostly with the high temperature exhaust of PGC and the high frequency of its opeRation. Numerical simulations can provide important insights into PGC exhaust flow and its interaction with turbine blades. In this paper, a Rotating Detonation Combustor (RDC) and a row of nozzle guide vanes have been modeled based on the data from literature and an available experimental setup at TU Berlin. Five guide vane configuRations with different geometrical parameters have been modeled. URANS simulations were done for all guide vane arrangements to investigate the effect of solidity and blade type representing different outlet restrictions on the RDC exhaust flow. Total pressure loss and velocity fluctuation were computed upstream and downstream of the vanes. The results analzed the connection between total pressure loss and the vanes solidity and thickness to chord Ratio. It is observed that more than 57% of the upstream velocity angle fluctuation amplitude was damped by the vanes. Furthermore, the area reduction was found to be the significant driving factor for damping the velocity angle fluctuations, whether in the form of solidity or thickness on chord Ratio increment. A further study of the flow field details revealed that the vane passages act as convergent divergent nozzles in the unsteady flow field and no compression wave exists upstream. This RDC exhaust flow investigation is an important primary step from a turbomachinery standpoint, which provided details of blade behavior in such an unsteady flow field.
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Implementation of the “Virtual Camber” Transformation into the Open Source Software QBlade: Validation and Assessment
Energy Procedia, 2018Co-Authors: Alessandro Bianchini, David Marten, Andrea Tonini, Francesco Balduzzi, Christian Navid Nayeri, Giovanni Ferrara, Christian Oliver PaschereitAbstract:Abstract Thanks to the renewed interest in vertical-axis wind turbines, research efforts are devoted at improving the accuracy of present simulation tools, many of which are underdeveloped if compared to those for horizontal-axis turbines. In particular, recent studies demonstrated that a correction for the “virtual camber” effect has a major impact on the simulation. In cycloidal motion indeed the blade aerodynamics are equivalent to those of a virtually-transformed airfoil with a camber line defined by its arc of rotation. In this study, the implementation of a specific module to account for the virtual camber effect in the Open-Source code QBlade is presented. The effectiveness of the model is then validated by four 1-blade and a full 3-blade H-Darrieus turbines, for which both experimental measurements and detailed CFD calculations were available. A sensitivity analysis on the impact of the virtual camber correction on the accuracy of a low-order simulation model has been carried out as a function of the chord-to-radius Ratio and the airfoil Thickness-to-Chord Ratio. Reference thresholds for the model applicability are presented for both variables.
Ujjwal K. Saha - One of the best experts on this subject based on the ideXlab platform.
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On the influence of blade Thickness-to-Chord Ratio on dynamic stall phenomenon in H-type Darrieus wind rotors
Energy Conversion and Management, 2020Co-Authors: Siddhant Jain, Ujjwal K. SahaAbstract:Abstract The present work examines the influence of blade Thickness-to-Chord Ratio (t/c) on dynamic stall phenomenon in an H-type Darrieus wind rotor. A 2D incompressible numerical study is conducted on a single-bladed rotor at a tip speed Ratio (TSR) of 2 with a motivation to understand the intricate flow physics around the blade by employing a transitional shear stress transport (TSST) model. Five different t/c Ratios (9%, 12%, 15%, 18% and 21%) have been studied for symmetrical NACA airfoils. It is found that in case of thinner airfoils (t/c = 9% and 12%), the formation of the dynamic stall vortex (DSV) is preceded by the formation and bursting of leading edge (LE) laminar sepaRation bubble (LSB) leading to a more abrupt LE type stall. For t/c = 15%, a mixed type stall is observed with LSBs distributed over the airfoil resulting in two coherent vortex structures that subsequently merge to form the DSV. A trailing edge (TE) type stall was observed in case of thicker airfoils (t/c = 18% and 21%). The largest peak in the lift and drag coefficients (Cl, Cd) values of 1.87 and 1.27, respectively are obtained with the thinnest airfoil. However, the largest peak in the moment coefficient (Cm) value is achieved with t/c = 12%. Further, due to the DSV sepaRation at the lift stall point, a further increase of 6.3%, 7.1%, 1.5%, 8.94% and 11.8% in Cd values is observed for increasing order of t/c. Overall, the study sheds light on the capability of TSST model in capturing the dynamic stall phenomenon efficiently.
Guillermo García-valdecasas - One of the best experts on this subject based on the ideXlab platform.
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The Effect of Airfoil Thickness on the Efficiency of Low-Pressure Turbines
Journal of Turbomachinery, 2013Co-Authors: Diego Torre, Raúl Vázquez, Leyre Armañanzas, Fernando Partida, Guillermo García-valdecasasAbstract: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.
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The Effect of Airfoil Thickness on the Efficiency of LP Turbines
Volume 8: Turbomachinery Parts A B and C, 2012Co-Authors: Diego Torre, Raúl Vázquez, Leyre Armañanzas, Fernando Partida, Guillermo García-valdecasasAbstract: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.Copyright © 2012 by ASME
Ajit R Godbole - One of the best experts on this subject based on the ideXlab platform.
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An improved dynamic stall model and its effect on wind turbine fatigue load prediction
Renewable Energy, 2020Co-Authors: Xiong Liu, Shi Liang, Ajit R GodboleAbstract:Abstract Due to the nature of the atmospheric boundary layer, large Horizontal-Axis Wind Turbines (HAWTs) generally operate in highly unstable environment, leading to nonstationary loads on HAWT structures. Therefore, it is important to accurately estimate the nonstationary loads to ensure appropriate design boundaries. In this paper, an improved dynamic stall model based on the Beddoes-Leishman (B-L) model is proposed for the estimation of nonstationary aerodynamic loads. The B-L model is modified to account for the characteristics of wind turbine aerofoils which operate at lower Mach numbers and have a larger Thickness-to-Chord Ratio compared to aviation aerofoils. Validation of the model is performed extensively through simulations of the S809 aerofoil under pitch oscillation with different mean angles of attack, oscillating amplitudes and reduced frequencies. To understand the effects of the modifications introduced to the dynamic stall model on the aerodynamic fatigue loads over the lifetime of a wind turbine, a load analysis of a 2 MW HAWT is conducted. The load analysis uses the Blade-Element Momentum (BEM) theory in conjunction with the dynamic stall models. The presented modified dynamic stall model is applicable to wind turbine aerofoils with relative thicknesses greater than 15%.