Harry W . M . Hoeijmakers | University of Twente (original) (raw)
Papers by Harry W . M . Hoeijmakers
The relation between the parameters of the body-force field generated by a plasma actuator and th... more The relation between the parameters of the body-force field generated by a plasma actuator and the maximum induced velocity in quiescent air is investigated by expressing the body-force distribution as the Gaussian function of the spatial coordinates. The aim of this study is to identify the dominant parameters for modeling of the body-force distribution. For that purpose, the parametric study using numerical simulations and dimensional analysis are conducted to derive the nondimensional key parameters. It is found that the nondimensional maximum induced velocity is determined by the Reynolds number calculated by three parameters: the total induced momentum per unit time, the height of the center of gravity of the body-force distribution, and the standard deviation from the center of gravity. In addition, the relation for the Gaussian body-force distribution turns out to be applicable to a conventional model, i.e, the Suzen model, even though the shapes of the distribution differ. T...
The effects of a pulse actuation on the Lagrangian Coherent Structures (LCS) in the separated flo... more The effects of a pulse actuation on the Lagrangian Coherent Structures (LCS) in the separated flow over a NACA 65(1)-412 airfoil at low Reynolds number is investigated. A computational parametric study is performed on the effect of location over the suction side of the airfoil. An increased local separation angle leads to flow reattachment of the Lagrangian material line. Reattachment is accompanied by an increase in the lift and reduction in drag. The optimal pulse actuation is near the Lagrangian separation point.
The Proceedings of The Computational Mechanics Conference, 2018
Theoretical and Computational Fluid Dynamics, 2018
This study investigates the relationship between body-force fields and maximum velocity induced i... more This study investigates the relationship between body-force fields and maximum velocity induced in quiescent air for development of a simple body-force model of a plasma actuator. Numerical simulations are conducted with the body force near a wall. The spatial distribution and temporal variation of the body force are a Gaussian distribution and steady actuation, respectively. The dimensional analysis is performed to derive a reference velocity and Reynolds number based on the body-force distribution. It is found that the derived Reynolds number correlates well with the nondimensional maximum velocity induced in quiescent conditions when the center of the Gaussian distribution is fixed at the wall. Additionally, two flow regimes are identified in terms of the Reynolds number. Considering the variation of the center of gravity of force fields, another Reynolds number is defined by introducing a new reference length. The nondimensional maximum velocity is found to be scaled with the latter Reynolds number, i.e., the maximum induced velocity in quiescent conditions is determined from three key parameters of the force field: the total induced momentum per unit time, the height of the center of gravity, and the standard deviation from it. This scaling turns out to be applicable to existing body-force models of the plasma actuator, despite the force distributions different from the Gaussian distribution. Comparisons of velocity profiles with experimental data validate the results and show that the flow induced by a plasma actuator can be simulated with simple force distributions by adjustment of the key body-force parameters. Keywords Flow control • Force-induced flow • Body-force model of plasma actuator • Dimensional analysis Communicated by M. R. Malik.
29th AIAA Applied Aerodynamics Conference, 2011
eld and underlying body forces (i.e. performance) of a plasma actuator and provide input data for... more eld and underlying body forces (i.e. performance) of a plasma actuator and provide input data for the numerical analysis. The numerical work consists of the implementation of a basic electro-static model that can be used for quick analysis of the plasma actuator design. Using the model an estimation of the body force and induced velocity is obtained. Computational Fluid Dynamics (CFD) simulations have been performed for a NACA-0018 airfoil section with emulated plasma actuators distributed along its contour to investigate dierent strategies for ow control. This investigation shows that present-day plasma actuators are useable for both separation control and load control at lower free-stream velocities but are currently not powerful enough for load control at higher free-stream speeds. Fortunately, many improvements are possible that could lead to optimization of plasma-actuated ow control.
Volume 2: CFD and VIV, 2014
To control underwater vehicles appendages such as rudders or fins are generally used. These appen... more To control underwater vehicles appendages such as rudders or fins are generally used. These appendages induce added resistance and deteriorate the quality of the inflow to aft control surfaces or propeller, due to the formation of amongst others horseshoe vortices. In this paper, CFD is used to study the flow around a typical wing-body junction and to obtain insight in how to suppress the horseshoe vortex. For a generic submarine the impact of a range of modifications of the sail on resistance, propulsion and wake field is investigated. Design guidelines regarding the most promising modifications will be given. It will be shown that quite significant improvements of the resistance as well as the wake quality can be obtained by properly designing the junction between the appendage and the hull.
Computational Fluid Dynamics 2008, 2009
This paper describes an investigation of the mechanisms producing thrust for an airfoil performin... more This paper describes an investigation of the mechanisms producing thrust for an airfoil performing a pitching or heaving motion in a low Reynoldsnumber flow (Re = 1000, based on chord length) by analysis of numerically obtained flow fields and forces on the airfoil. For heaving motion the dependence on reduced frequency and non-dimensional heaving amplitude are examined. For pitching motion the reduced frequency and the center of rotation are varied. The vortex generated by the leading edge is found to be determinant for thrust by heaving motion. Pitching propulsion is shown to be an effect of coupled acceleration and inclination of the airfoil.
48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 2010
19th AIAA Computational Fluid Dynamics, 2009
To accurately capture vortical flow structures on r elatively coarse grids, vorticity confinement... more To accurately capture vortical flow structures on r elatively coarse grids, vorticity confinement might provide a cost-effective technique t o counter the vorticity diffusing effect of numerical dissipation. Properties of the confinemen t term, added to the momentum equation, are studied analytically and numerically. Two variants of vorticity confinement have been implemented in a finite-volume method for solving the Euler equations: one for uniform structured grids and one for unstructured grids. The method is applied to the flow about a complex wing geometry which generates a compact tip vortex. It is shown that vorticity confinement preserves the vortical structure r easonably well, however, the solution is sensitive to the value of the confinement coefficie nt.
Journal of Geophysical Research, 2007
Take-down policy If you believe that this document breaches copyright please contact us providing... more Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
AIAA Journal
In supersonic-combustion ramjets (scramjets), fuel is injected, which should mix rapidly with the... more In supersonic-combustion ramjets (scramjets), fuel is injected, which should mix rapidly with the supersonic crossflow to minimize the length of the scramjet. Tandem dual-jet injection has shown improved mixing performance over single-jet injection. However, experiments on tandem dual-jet injection have not addressed the jet shear layer, in which the mixing occurs, yet. The present study investigates the jet shear layer, as well as the bow shocks in front of the jets, in a continuous air-indraft supersonic wind tunnel at Mach number 1.55. A schlieren setup has been used for visualizing the flow features. A largely automated algorithm for processing schlieren images has been developed to determine the location of the upper boundary of the jet shear layer. The penetration of the jet is studied as a function of 1) J, the ratio of the momentum of the jet and that of the crossflow, and 2) the dimensionless distance S between the dual-jets. An empirical similarity relation has been established for the time-averaged location of the jet upper shear layer as function of J and S, covering the investigated conditions (J ∈ 2.8;3.8;4.8, S ∈ 0∶9.87). This empirical similarity relation provides S opt , the spacing for maximal penetration of the jets as function of J.
Extended abstract Results are presented of a study on utilising Vertical-Cavity-Surface-Emitting-... more Extended abstract Results are presented of a study on utilising Vertical-Cavity-Surface-Emitting-Laser (VCSEL) driven Schlieren visualization of cascaded injection in a supersonic flow. The background of the study is fuel injection within a supersonic combustion ramjet (scramjet). The scramjet is a ramjet airbreathing jet engine in which combustion takes place in a supersonic air flow. Scramjets promise significant economic advantages over rocket-based flight travel. However, at hypersonic flight speeds the compressibility effects delay shear layer mixing. In order to maintain for scramjets, the fuel-air mixture required for high combustion efficiency, the combustor becomes relatively long 1. In the present case of cascaded injection, the downstream injector benefits from the shielding effect induced by the smaller upstream injector. This provides a reduction of the momentum in the flow, allowing better penetration of fuel in the air stream over a shorter length. Validation of theor...
In the present paper analytical and numerical results obtained for the problem of acoustic radiat... more In the present paper analytical and numerical results obtained for the problem of acoustic radiation from a vibrating wall segment inside an infinite rectangular duct with uniform mean flow are presented and compared. The numerical results are obtained employing a recently developed Discontinuous Galerkin finite element method implemented on a tetrahedral grid. The presented leading term in the analytical solution, which represents a propagating plane wave, is shown to capture most of the characteristics of the solution. For the plane wave a closed form solution is presented for two specific wall vibration velocities. The remainder of the analytical solution is given by an infinite number of ’diffracted waves’ (waves affected by reflection, scattering, diffraction, etc.). For the diffracted waves, which are decaying modes, only an approximate solution has been obtained employing the method of stationary phase. Only near the vibrating wall segment the influence of the diffracted wave...
The occurrence of cavitation is one of the main limiting factors in the operation and design of c... more The occurrence of cavitation is one of the main limiting factors in the operation and design of centrifugal pumps. In this paper a model for the prediction of sheet cavitation is described. This model has been implemented in a threedimensional finite-element package, employing the potentialflow approximation of the governing flow equations. At the interface between vapor and liquid, pressure equilibrium is required. The closure region of the cavity is modeled as the collapse of a bubble, whose motion is described by the Rayleigh-Plesset equation. The effect of displacement of the flow due to presence of the sheet cavity is incorporated by the transpiration technique. This is a linearised approach which is well-known from techniques for coupling inviscid-flow methods to boundary-layer methods. The model gives the location of the sheet cavity (if present); its length is thus also predicted. The model has been validated by comparing sheet cavitation at the blades of a centrifugal pump ...
34th Wind Energy Symposium, 2016
An improved formulation of drag estimation for thick airfoils is presented. Drag underprediction ... more An improved formulation of drag estimation for thick airfoils is presented. Drag underprediction in XFOIL like viscous-inviscid interaction methods can be quite significant for thick airfoils used in wind turbine applications (up to 30% as seen in the present study). The improved drag formulation predicts the drag accurately for airfoils with reasonably small trailing edge thickness. The derivation of drag correction is based on the difference between the actual momentum loss thickness based on free stream velocity and the one based on the velocity at the edge of the boundary layer. The improved formulation is implemented in the most recent version of XFOIL and RFOIL (an aerodynamic design and analysis method based on XFOIL, developed by a consortium of ECN, NLR and TU Delft after ECN acquired the XFOIL code. After 1996, ECN maintained and improved the tool.) and the results are compared with experimental data, results from commercial CFD methods like ANSYS CFX and other methods like DTU-AED EllipSys2D and CENER WMB. The improved version of RFOIL shows good agreement with experimental data. Nomenclature α Angle of attack ∆θ Error in θ δ Boundary layer thickness δ * Boundary layer displacement thickness ∞ Subscript for incident free stream condition ρ Density of fluid θ Boundary layer momentum thickness ξ, η Streamline space coordinates A, B G − β equilibrium locus coefficients airf oil Subscript for airfoil parameters c Airfoil chord length C τ EQ Equilibrium maximum shear stress coefficient c d Sectional drag coefficient c l Sectional lift coefficient D Drag e Subscript for boundary layer edge condition
SAE Technical Paper Series, 2015
SAE Technical Paper Series, 2015
34th Wind Energy Symposium, 2016
An improved formulation of drag estimation for thick airfoils is presented. Drag underprediction ... more An improved formulation of drag estimation for thick airfoils is presented. Drag underprediction in XFOIL like viscous-inviscid interaction methods can be quite significant for thick airfoils used in wind turbine applications (up to 30% as seen in the present study). The improved drag formulation predicts the drag accurately for airfoils with reasonably small trailing edge thickness. The derivation of drag correction is based on the difference between the actual momentum loss thickness based on free stream velocity and the one based on the velocity at the edge of the boundary layer. The improved formulation is implemented in the most recent version of XFOIL and RFOIL (an aerodynamic design and analysis method based on XFOIL, developed by a consortium of ECN, NLR and TU Delft after ECN acquired the XFOIL code. After 1996, ECN maintained and improved the tool.) and the results are compared with experimental data, results from commercial CFD methods like ANSYS CFX and other methods like DTU-AED EllipSys2D and CENER WMB. The improved version of RFOIL shows good agreement with experimental data. † Researcher, Wind Energy Unit, Westerduinweg 3, ramanujam@ecn.nl, Member AIAA ‡ Former M.Sc. Student, Sustainable Energy Technology, giridhar.
An improved formulation of drag estimation for thick airfoils is presented. Drag under-prediction... more An improved formulation of drag estimation for thick airfoils is presented. Drag under-prediction in XFOIL like viscous-inviscid interaction methods can be quite significant for thick airfoils used in wind turbine applications (up to 30% as seen in the present study). The improved drag formulation predicts the drag accurately for airfoils with reasonably small trailing edge thickness. The derivation of drag correction is based on the difference between the actual momentum loss thickness based on free stream velocity and the one based on the velocity at the edge of the boundary layer. The improved formulation is implemented in the most recent version of XFOIL and RFOIL (an aerodynamic design and analysis method based on XFOIL, developed by a consortium of ECN, NLR and TU Delft after ECN acquired the XFOIL code. After 1996, ECN maintained and improved the tool.) and the results are compared with experimental data, results from commercial CFD methods like ANSYS CFX and other methods like DTU-AED EllipSys2D and CENER WMB. The improved version of RFOIL shows good agreement with experimental data.
The relation between the parameters of the body-force field generated by a plasma actuator and th... more The relation between the parameters of the body-force field generated by a plasma actuator and the maximum induced velocity in quiescent air is investigated by expressing the body-force distribution as the Gaussian function of the spatial coordinates. The aim of this study is to identify the dominant parameters for modeling of the body-force distribution. For that purpose, the parametric study using numerical simulations and dimensional analysis are conducted to derive the nondimensional key parameters. It is found that the nondimensional maximum induced velocity is determined by the Reynolds number calculated by three parameters: the total induced momentum per unit time, the height of the center of gravity of the body-force distribution, and the standard deviation from the center of gravity. In addition, the relation for the Gaussian body-force distribution turns out to be applicable to a conventional model, i.e, the Suzen model, even though the shapes of the distribution differ. T...
The effects of a pulse actuation on the Lagrangian Coherent Structures (LCS) in the separated flo... more The effects of a pulse actuation on the Lagrangian Coherent Structures (LCS) in the separated flow over a NACA 65(1)-412 airfoil at low Reynolds number is investigated. A computational parametric study is performed on the effect of location over the suction side of the airfoil. An increased local separation angle leads to flow reattachment of the Lagrangian material line. Reattachment is accompanied by an increase in the lift and reduction in drag. The optimal pulse actuation is near the Lagrangian separation point.
The Proceedings of The Computational Mechanics Conference, 2018
Theoretical and Computational Fluid Dynamics, 2018
This study investigates the relationship between body-force fields and maximum velocity induced i... more This study investigates the relationship between body-force fields and maximum velocity induced in quiescent air for development of a simple body-force model of a plasma actuator. Numerical simulations are conducted with the body force near a wall. The spatial distribution and temporal variation of the body force are a Gaussian distribution and steady actuation, respectively. The dimensional analysis is performed to derive a reference velocity and Reynolds number based on the body-force distribution. It is found that the derived Reynolds number correlates well with the nondimensional maximum velocity induced in quiescent conditions when the center of the Gaussian distribution is fixed at the wall. Additionally, two flow regimes are identified in terms of the Reynolds number. Considering the variation of the center of gravity of force fields, another Reynolds number is defined by introducing a new reference length. The nondimensional maximum velocity is found to be scaled with the latter Reynolds number, i.e., the maximum induced velocity in quiescent conditions is determined from three key parameters of the force field: the total induced momentum per unit time, the height of the center of gravity, and the standard deviation from it. This scaling turns out to be applicable to existing body-force models of the plasma actuator, despite the force distributions different from the Gaussian distribution. Comparisons of velocity profiles with experimental data validate the results and show that the flow induced by a plasma actuator can be simulated with simple force distributions by adjustment of the key body-force parameters. Keywords Flow control • Force-induced flow • Body-force model of plasma actuator • Dimensional analysis Communicated by M. R. Malik.
29th AIAA Applied Aerodynamics Conference, 2011
eld and underlying body forces (i.e. performance) of a plasma actuator and provide input data for... more eld and underlying body forces (i.e. performance) of a plasma actuator and provide input data for the numerical analysis. The numerical work consists of the implementation of a basic electro-static model that can be used for quick analysis of the plasma actuator design. Using the model an estimation of the body force and induced velocity is obtained. Computational Fluid Dynamics (CFD) simulations have been performed for a NACA-0018 airfoil section with emulated plasma actuators distributed along its contour to investigate dierent strategies for ow control. This investigation shows that present-day plasma actuators are useable for both separation control and load control at lower free-stream velocities but are currently not powerful enough for load control at higher free-stream speeds. Fortunately, many improvements are possible that could lead to optimization of plasma-actuated ow control.
Volume 2: CFD and VIV, 2014
To control underwater vehicles appendages such as rudders or fins are generally used. These appen... more To control underwater vehicles appendages such as rudders or fins are generally used. These appendages induce added resistance and deteriorate the quality of the inflow to aft control surfaces or propeller, due to the formation of amongst others horseshoe vortices. In this paper, CFD is used to study the flow around a typical wing-body junction and to obtain insight in how to suppress the horseshoe vortex. For a generic submarine the impact of a range of modifications of the sail on resistance, propulsion and wake field is investigated. Design guidelines regarding the most promising modifications will be given. It will be shown that quite significant improvements of the resistance as well as the wake quality can be obtained by properly designing the junction between the appendage and the hull.
Computational Fluid Dynamics 2008, 2009
This paper describes an investigation of the mechanisms producing thrust for an airfoil performin... more This paper describes an investigation of the mechanisms producing thrust for an airfoil performing a pitching or heaving motion in a low Reynoldsnumber flow (Re = 1000, based on chord length) by analysis of numerically obtained flow fields and forces on the airfoil. For heaving motion the dependence on reduced frequency and non-dimensional heaving amplitude are examined. For pitching motion the reduced frequency and the center of rotation are varied. The vortex generated by the leading edge is found to be determinant for thrust by heaving motion. Pitching propulsion is shown to be an effect of coupled acceleration and inclination of the airfoil.
48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 2010
19th AIAA Computational Fluid Dynamics, 2009
To accurately capture vortical flow structures on r elatively coarse grids, vorticity confinement... more To accurately capture vortical flow structures on r elatively coarse grids, vorticity confinement might provide a cost-effective technique t o counter the vorticity diffusing effect of numerical dissipation. Properties of the confinemen t term, added to the momentum equation, are studied analytically and numerically. Two variants of vorticity confinement have been implemented in a finite-volume method for solving the Euler equations: one for uniform structured grids and one for unstructured grids. The method is applied to the flow about a complex wing geometry which generates a compact tip vortex. It is shown that vorticity confinement preserves the vortical structure r easonably well, however, the solution is sensitive to the value of the confinement coefficie nt.
Journal of Geophysical Research, 2007
Take-down policy If you believe that this document breaches copyright please contact us providing... more Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
AIAA Journal
In supersonic-combustion ramjets (scramjets), fuel is injected, which should mix rapidly with the... more In supersonic-combustion ramjets (scramjets), fuel is injected, which should mix rapidly with the supersonic crossflow to minimize the length of the scramjet. Tandem dual-jet injection has shown improved mixing performance over single-jet injection. However, experiments on tandem dual-jet injection have not addressed the jet shear layer, in which the mixing occurs, yet. The present study investigates the jet shear layer, as well as the bow shocks in front of the jets, in a continuous air-indraft supersonic wind tunnel at Mach number 1.55. A schlieren setup has been used for visualizing the flow features. A largely automated algorithm for processing schlieren images has been developed to determine the location of the upper boundary of the jet shear layer. The penetration of the jet is studied as a function of 1) J, the ratio of the momentum of the jet and that of the crossflow, and 2) the dimensionless distance S between the dual-jets. An empirical similarity relation has been established for the time-averaged location of the jet upper shear layer as function of J and S, covering the investigated conditions (J ∈ 2.8;3.8;4.8, S ∈ 0∶9.87). This empirical similarity relation provides S opt , the spacing for maximal penetration of the jets as function of J.
Extended abstract Results are presented of a study on utilising Vertical-Cavity-Surface-Emitting-... more Extended abstract Results are presented of a study on utilising Vertical-Cavity-Surface-Emitting-Laser (VCSEL) driven Schlieren visualization of cascaded injection in a supersonic flow. The background of the study is fuel injection within a supersonic combustion ramjet (scramjet). The scramjet is a ramjet airbreathing jet engine in which combustion takes place in a supersonic air flow. Scramjets promise significant economic advantages over rocket-based flight travel. However, at hypersonic flight speeds the compressibility effects delay shear layer mixing. In order to maintain for scramjets, the fuel-air mixture required for high combustion efficiency, the combustor becomes relatively long 1. In the present case of cascaded injection, the downstream injector benefits from the shielding effect induced by the smaller upstream injector. This provides a reduction of the momentum in the flow, allowing better penetration of fuel in the air stream over a shorter length. Validation of theor...
In the present paper analytical and numerical results obtained for the problem of acoustic radiat... more In the present paper analytical and numerical results obtained for the problem of acoustic radiation from a vibrating wall segment inside an infinite rectangular duct with uniform mean flow are presented and compared. The numerical results are obtained employing a recently developed Discontinuous Galerkin finite element method implemented on a tetrahedral grid. The presented leading term in the analytical solution, which represents a propagating plane wave, is shown to capture most of the characteristics of the solution. For the plane wave a closed form solution is presented for two specific wall vibration velocities. The remainder of the analytical solution is given by an infinite number of ’diffracted waves’ (waves affected by reflection, scattering, diffraction, etc.). For the diffracted waves, which are decaying modes, only an approximate solution has been obtained employing the method of stationary phase. Only near the vibrating wall segment the influence of the diffracted wave...
The occurrence of cavitation is one of the main limiting factors in the operation and design of c... more The occurrence of cavitation is one of the main limiting factors in the operation and design of centrifugal pumps. In this paper a model for the prediction of sheet cavitation is described. This model has been implemented in a threedimensional finite-element package, employing the potentialflow approximation of the governing flow equations. At the interface between vapor and liquid, pressure equilibrium is required. The closure region of the cavity is modeled as the collapse of a bubble, whose motion is described by the Rayleigh-Plesset equation. The effect of displacement of the flow due to presence of the sheet cavity is incorporated by the transpiration technique. This is a linearised approach which is well-known from techniques for coupling inviscid-flow methods to boundary-layer methods. The model gives the location of the sheet cavity (if present); its length is thus also predicted. The model has been validated by comparing sheet cavitation at the blades of a centrifugal pump ...
34th Wind Energy Symposium, 2016
An improved formulation of drag estimation for thick airfoils is presented. Drag underprediction ... more An improved formulation of drag estimation for thick airfoils is presented. Drag underprediction in XFOIL like viscous-inviscid interaction methods can be quite significant for thick airfoils used in wind turbine applications (up to 30% as seen in the present study). The improved drag formulation predicts the drag accurately for airfoils with reasonably small trailing edge thickness. The derivation of drag correction is based on the difference between the actual momentum loss thickness based on free stream velocity and the one based on the velocity at the edge of the boundary layer. The improved formulation is implemented in the most recent version of XFOIL and RFOIL (an aerodynamic design and analysis method based on XFOIL, developed by a consortium of ECN, NLR and TU Delft after ECN acquired the XFOIL code. After 1996, ECN maintained and improved the tool.) and the results are compared with experimental data, results from commercial CFD methods like ANSYS CFX and other methods like DTU-AED EllipSys2D and CENER WMB. The improved version of RFOIL shows good agreement with experimental data. Nomenclature α Angle of attack ∆θ Error in θ δ Boundary layer thickness δ * Boundary layer displacement thickness ∞ Subscript for incident free stream condition ρ Density of fluid θ Boundary layer momentum thickness ξ, η Streamline space coordinates A, B G − β equilibrium locus coefficients airf oil Subscript for airfoil parameters c Airfoil chord length C τ EQ Equilibrium maximum shear stress coefficient c d Sectional drag coefficient c l Sectional lift coefficient D Drag e Subscript for boundary layer edge condition
SAE Technical Paper Series, 2015
SAE Technical Paper Series, 2015
34th Wind Energy Symposium, 2016
An improved formulation of drag estimation for thick airfoils is presented. Drag underprediction ... more An improved formulation of drag estimation for thick airfoils is presented. Drag underprediction in XFOIL like viscous-inviscid interaction methods can be quite significant for thick airfoils used in wind turbine applications (up to 30% as seen in the present study). The improved drag formulation predicts the drag accurately for airfoils with reasonably small trailing edge thickness. The derivation of drag correction is based on the difference between the actual momentum loss thickness based on free stream velocity and the one based on the velocity at the edge of the boundary layer. The improved formulation is implemented in the most recent version of XFOIL and RFOIL (an aerodynamic design and analysis method based on XFOIL, developed by a consortium of ECN, NLR and TU Delft after ECN acquired the XFOIL code. After 1996, ECN maintained and improved the tool.) and the results are compared with experimental data, results from commercial CFD methods like ANSYS CFX and other methods like DTU-AED EllipSys2D and CENER WMB. The improved version of RFOIL shows good agreement with experimental data. † Researcher, Wind Energy Unit, Westerduinweg 3, ramanujam@ecn.nl, Member AIAA ‡ Former M.Sc. Student, Sustainable Energy Technology, giridhar.
An improved formulation of drag estimation for thick airfoils is presented. Drag under-prediction... more An improved formulation of drag estimation for thick airfoils is presented. Drag under-prediction in XFOIL like viscous-inviscid interaction methods can be quite significant for thick airfoils used in wind turbine applications (up to 30% as seen in the present study). The improved drag formulation predicts the drag accurately for airfoils with reasonably small trailing edge thickness. The derivation of drag correction is based on the difference between the actual momentum loss thickness based on free stream velocity and the one based on the velocity at the edge of the boundary layer. The improved formulation is implemented in the most recent version of XFOIL and RFOIL (an aerodynamic design and analysis method based on XFOIL, developed by a consortium of ECN, NLR and TU Delft after ECN acquired the XFOIL code. After 1996, ECN maintained and improved the tool.) and the results are compared with experimental data, results from commercial CFD methods like ANSYS CFX and other methods like DTU-AED EllipSys2D and CENER WMB. The improved version of RFOIL shows good agreement with experimental data.