Accurate delivery of cargo from air to ground is currently performed using autonomously guided pa... more Accurate delivery of cargo from air to ground is currently performed using autonomously guided parafoil systems. These parafoils offer limited maneuverability and accuracy, and are often relatively complex systems with significant deployment uncertainty. The author has proposed, designed, and developed a novel precision airdrop system in the form of a samara. Consisting of a single wing, payload, and control system, the guided samara is mechanically simple, and when correctly configured, is globally stable during deployment and steady descent. The proposed control mechanisms grant the vehicle omni-directional glide slope control during autorotating descent. This is the first documented effort to develop an actively controlled vehicle of this form factor. The research presented in this thesis includes the conceptual design of the vehicle and several
Viscous analysis is crucial for understanding aerodynamic performance metrics such as profile dra... more Viscous analysis is crucial for understanding aerodynamic performance metrics such as profile drag. For three-dimensional (3D) viscous analysis, Reynolds-averaged Navier-Stokes (RANS) solvers are often the fastest available tool in practice but the required computational efforts preclude its extensive use for preliminary design. In contrast, the integral boundary layer (IBL) method offers a computationally more efficient alternative with comparable effectiveness when applicable. However, existing IBL methods mostly rely on two-dimensional (2D) or quasi-2D assumptions and thus remain to be extended to a fully 3D formulation for general configurations. To this end, we continue the development of an IBL method with discontinuous Galerkin (DG) finite element discretization and strong viscous-inviscid coupling. The current work proposes a captured laminar-to-turbulent flow transition treatment for the IBL method that can be more conveniently extended to the 3D case compared to a previously examined fitted transition approach. The current captured transition treatment also leverages a more robust nonlinear solution method and achieves accurate solution of transitional flows. Moreover, correction to the standard DG discretization is introduced for well-behaved numerical solution. Numerical results of the proposed method in a 2D implementation compares well with XFOIL and demonstrate its capability for practical aerodynamic analysis with free transition.
L'invention concerne un avion comprenant une soufflante canalisee et un moteur pour entrainer... more L'invention concerne un avion comprenant une soufflante canalisee et un moteur pour entrainer cette soufflante canalisee. Cet avion comprend une pluralite d'ailettes montees mobiles sur l'avion a une extremite d'echappement sensiblement rectangulaire de l'avion. Chaque ailette est sensiblement rectangulaire ou carree. La pluralite d'ailettes est configuree pour modifier une zone de sortie de l'extremite d'echappement. L'avion comprend un circuit de detection pour detecter un regime du moteur ou pour produire un signal de regime. Cet avion comprend un circuit de commande relie au circuit de detection et a la pluralite d'ailettes. Le circuit de commande est concu pour actionner la pluralite d'ailettes pour modifier la zone de sortie de l'extremite d'echappement, de sorte a faire varier la charge de pression sur la soufflante canalisee, pour commander le regime du moteur, en reaction au signal de regime.
This chapter contains sections titled: D.1 Geometry and Problem Formulation, D.2 First-Order Solu... more This chapter contains sections titled: D.1 Geometry and Problem Formulation, D.2 First-Order Solution, D.3 First-Order Force and Moment Calculation, D.4 Second-Order Solution
This paper presents the results from initial flight tests of a 30% scale demonstrator of a blown-... more This paper presents the results from initial flight tests of a 30% scale demonstrator of a blown-wing SuperSTOL concept aircraft, intended for operation from extremely short runways of 100 ft or less. The subscale demonstrator is aimed at investigating the maximum achievable in-flight lift coe cients with the blown wing, as well as the control and handling qualities with a mostly conventional aircraft configuration with unblown control surfaces. With a relatively modest amount of blowing power-a static thrust/weight of 0.45-the flight tests show that the blown wing SuperSTOL concept can generate high lift coe cients greater than 10 in flight. It was observed that reducing the size of the propeller enabled larger C L values to be achieved. In high-C L flight the roll control authority of conventional ailerons was found to be marginal, partly due to the low fight dynamic pressure and partly due to the local stall over the unblown part of the aileron. In the configuration tested most of the elevator deflection was consumed to obtain pitch trim at low speed. A finite rotation rate to takeo attitude was found to significantly contribute to the ground roll distance. I. Nomenclature c airfoil chord c`2D airfoil lift coe cient C L 3D lift coe cient C X 3D net streamwise force coe. (= C D C T) c J 2D jet momentum-excess coe cient C J 3D jet momentum-excess coe cient E total aircraft energy h flight altitude h d 2D propulsor disk height S reference area V flight speed V J propeller jet speed W overall weight ↵ angle of attack flight path angle ⇢ air density ⌦ propeller rotation rate II. Introduction Recent work [1] [2] has proposed the use of super-short takeo and landing (SSTOL) aircraft for urban passenger transport missions. The SSTOL concept is a fixed wing vehicle which has infrastructure requirements that are competitive with vertical takeo and landing (VTOL) aircraft. Compared to the VTOL vehicles being widely proposed, SSTOL may o er advantages in terms of both certification and performance. Certification challenges for most distributed electric propulsion VTOL aircraft may arise from the fact that the propulsion system in hover provides both lift and attitude control. This coupling increases the criticality of power system failures, as well as requiring a fly-by-wire control system. This requires increased redundancy and complexity, adding cost and weight to the aircraft and time to the certification process [3]. A fixed-wing SSTOL aircraft, with an unpowered stall speed of less than 61 kts, would be comparable to existing single-engine aircraft in a common mode power system failure scenario, providing an established certification pathway. Additionally, due to the lower required thrust-to-weight ratio and improved cruise L/D of SSTOL aircraft, there are likely performance benefits in terms of range, cruise speed, and/or passengers capability for a given vehicle weight. If takeo and landing distances can be made comparable to the size of a vertiport, there may be substantial benefit to using SSTOL aircraft for many of the proposed urban air mobility missions. Distributed electric propulsion technology enables extreme short field performance because it is an e cient and mechanically simple means of having externally blown flaps along most of the wing span. The blowing jet is created by electric motors arranged along and under the leading edge of the wing; this jet enhances the lift of the wing through Graduate Student,
This paper presents a description of the physical principles of aerodynamic power savings from bo... more This paper presents a description of the physical principles of aerodynamic power savings from boundary layer ingestion propulsion and a quantitative evaluation of the boundary layer ingestion bene...
This paper presents experimental measurements of propulsive power reduction due to boundary layer... more This paper presents experimental measurements of propulsive power reduction due to boundary layer ingestion, for an electric ducted fan propulsor behind a NACA 0040 body of revolution at a Reynolds number of approximately 240,000. The propulsive power is defined as the electrical power required by the propulsor to obtain a zero net streamwise force on the body/propulsor combination, mimicking the cruise condition for an aircraft. The benefits of the boundary layer ingestion are quantified as a power saving coefficient, or ratio relative to the no-ingestion case where the propulsor is isolated from the wake. The measurements show a maximum power savings when the propulsor is closest to the body centered on the body axis, with savings of 26% for an untripped flow case and 29% for a tripped flow case. A second iteration of experiments were performed, showing a maximum power savings of 25% for a tripped flow case. Propulsor locations farther downstream and further off-axis show progressively smaller power saving benefits. An uncertainty analysis is performed to verify the measurements to within 99% confidence. Wake profiles were also measured to confirm that the wake was fully ingested for on-axis propulsor locations.
This paper presents the experimental assessment of the aerodynamic benefit of boundary layer inge... more This paper presents the experimental assessment of the aerodynamic benefit of boundary layer ingestion for an advanced design civil transport aircraft, the D8 "double bubble," carried out from 2010 to 2015 as part of a NASA N 3 Phase 2 Program. A back-to-back comparison of non-boundary layer ingesting and boundary layer ingesting versions of the D8 was conducted using 1:11-scale powered models in the NASA Langley 14-by 22-foot subsonic tunnel. The aerodynamic benefit of boundary layer ingestion, as quantified by the difference in mechanical flow power required with boundary layer ingestion relative to the non-boundary layer ingesting case, was measured using two different methods to be 8.6% at the simulated cruise condition when the same propulsors are used on the two configurations. The benefit is found to be insensitive to the various modeling and processing assumptions. A detailed error analysis shows that the benefit has an uncertainty fraction of 0.21 and a 95% confidence interval fraction of 0.035, thus giving high confidence to these results. This work represents the first measurement of boundary layer ingestion performance improvements for a realistic civil aircraft configuration and provides a proof-of-concept for the use of boundary layer ingestion to improve fuel efficiency of subsonic transports.
We present a novel closed-circuit ultra-compact wind tunnel with an 8:1 contraction ratio and hig... more We present a novel closed-circuit ultra-compact wind tunnel with an 8:1 contraction ratio and high flow quality. Its overall footprint area is less than half that of a conventional tunnel with the same test section size and same contraction ratio, enabling significantly smaller material and construction costs. The tunnel’s key features which enable the small footprint include a two-dimensional main diffuser, a minimum-length contraction, and expanding turning vanes with a 1.167:1 ratio in corner two and an aggressive 1.875:1 ratio in corner four. Separation in the latter is prevented using a screen and honeycomb integrated into each vane passage—the first time this has been used in a wind tunnel. The tunnel exhibits excellent flow quality with less than $$\pm 1$$ ± 1 % mean flow variation in the test section core and a freestream turbulence level of 0.03% at 12 m/s over a 4 Hz–20kHz bandwidth. Graphical abstract
This article presents first-of-a-kind measurements, and complementary computations, of the flow t... more This article presents first-of-a-kind measurements, and complementary computations, of the flow through the propulsion system of a boundary layer ingesting, twin-engine advanced civil transport aircraft configuration. The experiments were carried out in the NASA Langley 14- by 22-foot Subsonic Tunnel, using a 1:11 scale model of the D8 “double-bubble” aircraft with electric ducted fans providing propulsive power. Overall force and moment measurements and flow field surveys at the inlet and nozzle exit planes were obtained. The computations were carried out with the NASA OVERFLOW code. The measurements and computations were conducted for a range of aircraft angles of attack and propulsor powers representing operating points during the aircraft mission. Velocity and pressure distributions at the propulsor inlet and exit, and integral inlet distortion metrics, are presented to quantify the flow nonuniformity due to boundary layer ingestion. The distorted inflow exhibits qualitative and...
This addendum describes the additional variables and unsteady loads which appear when full dynami... more This addendum describes the additional variables and unsteady loads which appear when full dynamics are considered in ASWING. Other extensions include an unsteady liftting-line model and a structural damping model. A general unsteady atmospheric gust velocity field is also considered. The governing discrete equations for the extended model form a system of coupled 1st-order ODE's in time. These are numerically solved via implicit time marching. Both 1st-order and 2nd-order accurate time discretizations are considered. In addition to the nonlinear time marching, linearized unsteady analyses are derived, both for the forced-response case (Bode analysis), and for the natural-response case (Eigenmode analysis). A Reduced Order Model (ROM) is constructed using the eigenmodes as a basis, for the purpose of approximate but very fast forced-response calculations, and for control-law synthesis.
This book is intended to serve a diverse audience of students, scientists and engineers who are i... more This book is intended to serve a diverse audience of students, scientists and engineers who are interested in understanding and utilizing the concepts of flight dynamics. The following notes provide to the reader the basic principles based on a classical analytical approach. The concepts of controllability and maneuverability are detailed starting from the definition of stability and control of the equilibrium states. Equations for the estimation of hinge moments and stick force in steady and maneuvering flight are provided. The equations of motion are then extended to unsteady flight and a detailed analytical model is derived for dynamic stability analysis, including an interpretation of stability and control derivatives. Modal response of the vehicle in the longitudinal and lateral-directional plane is also reconstructed. The problems inherent to the evaluation of the flying qualities of a fixed-wing aircraft and the elements of parameter identification are also introduced. Finally, open and closed loop response to controls is discussed both in time and frequency domain
An interactive design and optimization framework for the development of multielement airfoils is ... more An interactive design and optimization framework for the development of multielement airfoils is presented. A zonal Euler/Boundary-layer flow solver is used as the underlying analysis method. The full Newton solution method of the solver permits effectively 'free" calculation of flowfield sensitivities to predefined airfoil element shape deformation modes, and also to rigid-body element translation and rotation modes. The sensitivity of any aerodynamic quantity of interest, including drag, to all the geometric parameters is thus obtained. Single-point and multi-point optimization and least-squares inverse techniques are constructed with the sensitivity information. Aerodynamic and geometric constraints are also readily incorporated. The method's ability to economically incorporate many design variables into interactively-specified design and/or optimization p r o b lems makes it particularly effective in multielement airfoil development. Applications are presented for: 1) Multi-point optimization of a novel two-element transonic cruise airfoil with a thickness constraint, and 2) C I .~.~ optimization of a fourelement landing configuration airfoil. 'A..oei.te Pd-r, Member AIAA.
The present work aims at predicting the formation of laminar separation bubbles (LSB) and the rel... more The present work aims at predicting the formation of laminar separation bubbles (LSB) and the related transition to turbulence by means of Implicit Large Eddy Simulations with a high-order Discontinuous Galerkin (DG) method. We focus on the flow around an SD7003 rectangular wing section at an angle of attack of 4 o degrees and consider two different Reynolds numbers of 10,000 and 60,000 in order to gain insight into the characteristics of the laminar and turbulent regimes. At Reynolds number 10,000 the flow remains laminar and essentially two dimensional over the wing surface, and only the wake appears to exhibit a turbulent behavior. For the case at Reynolds 60,000, the flow is unsteady over the upper wing surface and the time averaged streamlines show a separation bubble which starts at about 24% of the chord. A close to 51% of the chord, the flow is fully turbulent. These findings appear to be in agreement with previously published results despite the relatively coarse meshes employed, which suggest that the DG method used is particularly suited to simulate these flows. Finally, transition is found to be caused by unstable Tollmien-Schlichting (TS) waves, as revealed by the growth of the stream-wise amplification factor.
A new computational model for initial sizing and performance prediction of vertical axis wind tur... more A new computational model for initial sizing and performance prediction of vertical axis wind turbines is presented. The model uses a 2D hybrid dynamic vortex and blade element momentum approach. Each airfoil is modeled as a single vortex of time varying strength with an analytical model for the influence of the shed vorticity. The vortex strengths are calculated by imposing a flow tangency condition at the three-quarter chord location on each airfoil, modified in the case of stall. The total blade forces and the momentum-based streamtube deceleration are then obtained using pre-computed c d and cm 2D blade profile characteristics. Model fidelity is improved over previous models because flow curvature, dynamic vortices, blade interactions, static stall, and streamtube changes are all taken into account. Fast convergence is obtained for a large range of solidity and tip speed ratio, which allows optimization of various parameters, including blade pitch angle variation.
XFOIL-An analysis and design system for low Reynolds number airfoils. ... panel method with a Kar... more XFOIL-An analysis and design system for low Reynolds number airfoils. ... panel method with a Karman-Tsien compressibility correction is developed for direct and mixed-inverse modes. ... are treated, with an e exp 9-type amplification formulation determining the transition point. ...
Accurate delivery of cargo from air to ground is currently performed using autonomously guided pa... more Accurate delivery of cargo from air to ground is currently performed using autonomously guided parafoil systems. These parafoils offer limited maneuverability and accuracy, and are often relatively complex systems with significant deployment uncertainty. The author has proposed, designed, and developed a novel precision airdrop system in the form of a samara. Consisting of a single wing, payload, and control system, the guided samara is mechanically simple, and when correctly configured, is globally stable during deployment and steady descent. The proposed control mechanisms grant the vehicle omni-directional glide slope control during autorotating descent. This is the first documented effort to develop an actively controlled vehicle of this form factor. The research presented in this thesis includes the conceptual design of the vehicle and several
Viscous analysis is crucial for understanding aerodynamic performance metrics such as profile dra... more Viscous analysis is crucial for understanding aerodynamic performance metrics such as profile drag. For three-dimensional (3D) viscous analysis, Reynolds-averaged Navier-Stokes (RANS) solvers are often the fastest available tool in practice but the required computational efforts preclude its extensive use for preliminary design. In contrast, the integral boundary layer (IBL) method offers a computationally more efficient alternative with comparable effectiveness when applicable. However, existing IBL methods mostly rely on two-dimensional (2D) or quasi-2D assumptions and thus remain to be extended to a fully 3D formulation for general configurations. To this end, we continue the development of an IBL method with discontinuous Galerkin (DG) finite element discretization and strong viscous-inviscid coupling. The current work proposes a captured laminar-to-turbulent flow transition treatment for the IBL method that can be more conveniently extended to the 3D case compared to a previously examined fitted transition approach. The current captured transition treatment also leverages a more robust nonlinear solution method and achieves accurate solution of transitional flows. Moreover, correction to the standard DG discretization is introduced for well-behaved numerical solution. Numerical results of the proposed method in a 2D implementation compares well with XFOIL and demonstrate its capability for practical aerodynamic analysis with free transition.
L'invention concerne un avion comprenant une soufflante canalisee et un moteur pour entrainer... more L'invention concerne un avion comprenant une soufflante canalisee et un moteur pour entrainer cette soufflante canalisee. Cet avion comprend une pluralite d'ailettes montees mobiles sur l'avion a une extremite d'echappement sensiblement rectangulaire de l'avion. Chaque ailette est sensiblement rectangulaire ou carree. La pluralite d'ailettes est configuree pour modifier une zone de sortie de l'extremite d'echappement. L'avion comprend un circuit de detection pour detecter un regime du moteur ou pour produire un signal de regime. Cet avion comprend un circuit de commande relie au circuit de detection et a la pluralite d'ailettes. Le circuit de commande est concu pour actionner la pluralite d'ailettes pour modifier la zone de sortie de l'extremite d'echappement, de sorte a faire varier la charge de pression sur la soufflante canalisee, pour commander le regime du moteur, en reaction au signal de regime.
This chapter contains sections titled: D.1 Geometry and Problem Formulation, D.2 First-Order Solu... more This chapter contains sections titled: D.1 Geometry and Problem Formulation, D.2 First-Order Solution, D.3 First-Order Force and Moment Calculation, D.4 Second-Order Solution
This paper presents the results from initial flight tests of a 30% scale demonstrator of a blown-... more This paper presents the results from initial flight tests of a 30% scale demonstrator of a blown-wing SuperSTOL concept aircraft, intended for operation from extremely short runways of 100 ft or less. The subscale demonstrator is aimed at investigating the maximum achievable in-flight lift coe cients with the blown wing, as well as the control and handling qualities with a mostly conventional aircraft configuration with unblown control surfaces. With a relatively modest amount of blowing power-a static thrust/weight of 0.45-the flight tests show that the blown wing SuperSTOL concept can generate high lift coe cients greater than 10 in flight. It was observed that reducing the size of the propeller enabled larger C L values to be achieved. In high-C L flight the roll control authority of conventional ailerons was found to be marginal, partly due to the low fight dynamic pressure and partly due to the local stall over the unblown part of the aileron. In the configuration tested most of the elevator deflection was consumed to obtain pitch trim at low speed. A finite rotation rate to takeo attitude was found to significantly contribute to the ground roll distance. I. Nomenclature c airfoil chord c`2D airfoil lift coe cient C L 3D lift coe cient C X 3D net streamwise force coe. (= C D C T) c J 2D jet momentum-excess coe cient C J 3D jet momentum-excess coe cient E total aircraft energy h flight altitude h d 2D propulsor disk height S reference area V flight speed V J propeller jet speed W overall weight ↵ angle of attack flight path angle ⇢ air density ⌦ propeller rotation rate II. Introduction Recent work [1] [2] has proposed the use of super-short takeo and landing (SSTOL) aircraft for urban passenger transport missions. The SSTOL concept is a fixed wing vehicle which has infrastructure requirements that are competitive with vertical takeo and landing (VTOL) aircraft. Compared to the VTOL vehicles being widely proposed, SSTOL may o er advantages in terms of both certification and performance. Certification challenges for most distributed electric propulsion VTOL aircraft may arise from the fact that the propulsion system in hover provides both lift and attitude control. This coupling increases the criticality of power system failures, as well as requiring a fly-by-wire control system. This requires increased redundancy and complexity, adding cost and weight to the aircraft and time to the certification process [3]. A fixed-wing SSTOL aircraft, with an unpowered stall speed of less than 61 kts, would be comparable to existing single-engine aircraft in a common mode power system failure scenario, providing an established certification pathway. Additionally, due to the lower required thrust-to-weight ratio and improved cruise L/D of SSTOL aircraft, there are likely performance benefits in terms of range, cruise speed, and/or passengers capability for a given vehicle weight. If takeo and landing distances can be made comparable to the size of a vertiport, there may be substantial benefit to using SSTOL aircraft for many of the proposed urban air mobility missions. Distributed electric propulsion technology enables extreme short field performance because it is an e cient and mechanically simple means of having externally blown flaps along most of the wing span. The blowing jet is created by electric motors arranged along and under the leading edge of the wing; this jet enhances the lift of the wing through Graduate Student,
This paper presents a description of the physical principles of aerodynamic power savings from bo... more This paper presents a description of the physical principles of aerodynamic power savings from boundary layer ingestion propulsion and a quantitative evaluation of the boundary layer ingestion bene...
This paper presents experimental measurements of propulsive power reduction due to boundary layer... more This paper presents experimental measurements of propulsive power reduction due to boundary layer ingestion, for an electric ducted fan propulsor behind a NACA 0040 body of revolution at a Reynolds number of approximately 240,000. The propulsive power is defined as the electrical power required by the propulsor to obtain a zero net streamwise force on the body/propulsor combination, mimicking the cruise condition for an aircraft. The benefits of the boundary layer ingestion are quantified as a power saving coefficient, or ratio relative to the no-ingestion case where the propulsor is isolated from the wake. The measurements show a maximum power savings when the propulsor is closest to the body centered on the body axis, with savings of 26% for an untripped flow case and 29% for a tripped flow case. A second iteration of experiments were performed, showing a maximum power savings of 25% for a tripped flow case. Propulsor locations farther downstream and further off-axis show progressively smaller power saving benefits. An uncertainty analysis is performed to verify the measurements to within 99% confidence. Wake profiles were also measured to confirm that the wake was fully ingested for on-axis propulsor locations.
This paper presents the experimental assessment of the aerodynamic benefit of boundary layer inge... more This paper presents the experimental assessment of the aerodynamic benefit of boundary layer ingestion for an advanced design civil transport aircraft, the D8 "double bubble," carried out from 2010 to 2015 as part of a NASA N 3 Phase 2 Program. A back-to-back comparison of non-boundary layer ingesting and boundary layer ingesting versions of the D8 was conducted using 1:11-scale powered models in the NASA Langley 14-by 22-foot subsonic tunnel. The aerodynamic benefit of boundary layer ingestion, as quantified by the difference in mechanical flow power required with boundary layer ingestion relative to the non-boundary layer ingesting case, was measured using two different methods to be 8.6% at the simulated cruise condition when the same propulsors are used on the two configurations. The benefit is found to be insensitive to the various modeling and processing assumptions. A detailed error analysis shows that the benefit has an uncertainty fraction of 0.21 and a 95% confidence interval fraction of 0.035, thus giving high confidence to these results. This work represents the first measurement of boundary layer ingestion performance improvements for a realistic civil aircraft configuration and provides a proof-of-concept for the use of boundary layer ingestion to improve fuel efficiency of subsonic transports.
We present a novel closed-circuit ultra-compact wind tunnel with an 8:1 contraction ratio and hig... more We present a novel closed-circuit ultra-compact wind tunnel with an 8:1 contraction ratio and high flow quality. Its overall footprint area is less than half that of a conventional tunnel with the same test section size and same contraction ratio, enabling significantly smaller material and construction costs. The tunnel’s key features which enable the small footprint include a two-dimensional main diffuser, a minimum-length contraction, and expanding turning vanes with a 1.167:1 ratio in corner two and an aggressive 1.875:1 ratio in corner four. Separation in the latter is prevented using a screen and honeycomb integrated into each vane passage—the first time this has been used in a wind tunnel. The tunnel exhibits excellent flow quality with less than $$\pm 1$$ ± 1 % mean flow variation in the test section core and a freestream turbulence level of 0.03% at 12 m/s over a 4 Hz–20kHz bandwidth. Graphical abstract
This article presents first-of-a-kind measurements, and complementary computations, of the flow t... more This article presents first-of-a-kind measurements, and complementary computations, of the flow through the propulsion system of a boundary layer ingesting, twin-engine advanced civil transport aircraft configuration. The experiments were carried out in the NASA Langley 14- by 22-foot Subsonic Tunnel, using a 1:11 scale model of the D8 “double-bubble” aircraft with electric ducted fans providing propulsive power. Overall force and moment measurements and flow field surveys at the inlet and nozzle exit planes were obtained. The computations were carried out with the NASA OVERFLOW code. The measurements and computations were conducted for a range of aircraft angles of attack and propulsor powers representing operating points during the aircraft mission. Velocity and pressure distributions at the propulsor inlet and exit, and integral inlet distortion metrics, are presented to quantify the flow nonuniformity due to boundary layer ingestion. The distorted inflow exhibits qualitative and...
This addendum describes the additional variables and unsteady loads which appear when full dynami... more This addendum describes the additional variables and unsteady loads which appear when full dynamics are considered in ASWING. Other extensions include an unsteady liftting-line model and a structural damping model. A general unsteady atmospheric gust velocity field is also considered. The governing discrete equations for the extended model form a system of coupled 1st-order ODE's in time. These are numerically solved via implicit time marching. Both 1st-order and 2nd-order accurate time discretizations are considered. In addition to the nonlinear time marching, linearized unsteady analyses are derived, both for the forced-response case (Bode analysis), and for the natural-response case (Eigenmode analysis). A Reduced Order Model (ROM) is constructed using the eigenmodes as a basis, for the purpose of approximate but very fast forced-response calculations, and for control-law synthesis.
This book is intended to serve a diverse audience of students, scientists and engineers who are i... more This book is intended to serve a diverse audience of students, scientists and engineers who are interested in understanding and utilizing the concepts of flight dynamics. The following notes provide to the reader the basic principles based on a classical analytical approach. The concepts of controllability and maneuverability are detailed starting from the definition of stability and control of the equilibrium states. Equations for the estimation of hinge moments and stick force in steady and maneuvering flight are provided. The equations of motion are then extended to unsteady flight and a detailed analytical model is derived for dynamic stability analysis, including an interpretation of stability and control derivatives. Modal response of the vehicle in the longitudinal and lateral-directional plane is also reconstructed. The problems inherent to the evaluation of the flying qualities of a fixed-wing aircraft and the elements of parameter identification are also introduced. Finally, open and closed loop response to controls is discussed both in time and frequency domain
An interactive design and optimization framework for the development of multielement airfoils is ... more An interactive design and optimization framework for the development of multielement airfoils is presented. A zonal Euler/Boundary-layer flow solver is used as the underlying analysis method. The full Newton solution method of the solver permits effectively 'free" calculation of flowfield sensitivities to predefined airfoil element shape deformation modes, and also to rigid-body element translation and rotation modes. The sensitivity of any aerodynamic quantity of interest, including drag, to all the geometric parameters is thus obtained. Single-point and multi-point optimization and least-squares inverse techniques are constructed with the sensitivity information. Aerodynamic and geometric constraints are also readily incorporated. The method's ability to economically incorporate many design variables into interactively-specified design and/or optimization p r o b lems makes it particularly effective in multielement airfoil development. Applications are presented for: 1) Multi-point optimization of a novel two-element transonic cruise airfoil with a thickness constraint, and 2) C I .~.~ optimization of a fourelement landing configuration airfoil. 'A..oei.te Pd-r, Member AIAA.
The present work aims at predicting the formation of laminar separation bubbles (LSB) and the rel... more The present work aims at predicting the formation of laminar separation bubbles (LSB) and the related transition to turbulence by means of Implicit Large Eddy Simulations with a high-order Discontinuous Galerkin (DG) method. We focus on the flow around an SD7003 rectangular wing section at an angle of attack of 4 o degrees and consider two different Reynolds numbers of 10,000 and 60,000 in order to gain insight into the characteristics of the laminar and turbulent regimes. At Reynolds number 10,000 the flow remains laminar and essentially two dimensional over the wing surface, and only the wake appears to exhibit a turbulent behavior. For the case at Reynolds 60,000, the flow is unsteady over the upper wing surface and the time averaged streamlines show a separation bubble which starts at about 24% of the chord. A close to 51% of the chord, the flow is fully turbulent. These findings appear to be in agreement with previously published results despite the relatively coarse meshes employed, which suggest that the DG method used is particularly suited to simulate these flows. Finally, transition is found to be caused by unstable Tollmien-Schlichting (TS) waves, as revealed by the growth of the stream-wise amplification factor.
A new computational model for initial sizing and performance prediction of vertical axis wind tur... more A new computational model for initial sizing and performance prediction of vertical axis wind turbines is presented. The model uses a 2D hybrid dynamic vortex and blade element momentum approach. Each airfoil is modeled as a single vortex of time varying strength with an analytical model for the influence of the shed vorticity. The vortex strengths are calculated by imposing a flow tangency condition at the three-quarter chord location on each airfoil, modified in the case of stall. The total blade forces and the momentum-based streamtube deceleration are then obtained using pre-computed c d and cm 2D blade profile characteristics. Model fidelity is improved over previous models because flow curvature, dynamic vortices, blade interactions, static stall, and streamtube changes are all taken into account. Fast convergence is obtained for a large range of solidity and tip speed ratio, which allows optimization of various parameters, including blade pitch angle variation.
XFOIL-An analysis and design system for low Reynolds number airfoils. ... panel method with a Kar... more XFOIL-An analysis and design system for low Reynolds number airfoils. ... panel method with a Karman-Tsien compressibility correction is developed for direct and mixed-inverse modes. ... are treated, with an e exp 9-type amplification formulation determining the transition point. ...
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Papers by Mark Drela