Jean-Jacques Chattot

Conceptual design and simulation of a small hybrid-electric unmanned aerial vehicle

Parallel hybrid-electric propulsion systems would be beneficial for small unmanned aerial vehicles used for military, homeland security, and disaster-monitoring missions involving intelligence, surveillance, or reconnaissance (ISR). The benefits include increased time on station and range as compared to electric-powered unmanned aerial vehicles and reduced acoustic and thermal signatures not available with gasoline-powered unmanned aerial vehicles. A conceptual design of a small unmanned aerial vehicle with a parallel hybrid-electric propulsion system, the application of a rule-based controller to the hybrid-electric system, and simulation results are provided. The two-point conceptual design includes an internal combustion engine sized for cruise speed and an electric motor and lithium-ion battery pack sized for endurance speed. A rule-based controller based on ideal operating line concepts is applied to the control of the parallel hybrid-electric propulsion system. The energy use for the 13.6 kg (30 Ib) hybrid-electric unmanned aerial vehicle with the rule-based controller during one-hour and three-hour ISR missions is 54% and 22% less, respectively, than for a four-stroke gasoline-powered unmanned aerial vehicle.

Optimization of Wind Turbines Using Helicoidal Vortex Model

The problem of the design of a wind turbine for maximum output is addressed from an aerodynamical point of view. It is shown that the optimum inviscid design, based on the Goldstein model, satisfies the minimum energy condition of Betz only in the limit of light loading. The more general equation governing the optimum is derived and an integral relation is obtained, stating that the optimum solution satisfies the minimum energy condition of Betz in the Trefftz plane in the average. The discretization of the problem is detailed, including the viscous correction based on the 2-D viscous profile data. A constraint is added to account for the thrust on the tower. The minimization problem is solved very efficiently by relaxation. Several optimized solutions are calculated and compared with the National Renewable Energy Laboratory (NREL) rotor, using the same profile, but different chord and twist distributions. In all cases, the optimization produces a more efficient design.

Characterization of Three-Dimensional Effects for the Rotating and Parked NREL Phase VI Wind Turbine

This paper addresses three-dimensional effects which are pertinent to wind turbine aerodynamics. Two computational models were applied to the National Renewable Energy Laboratory Phase VI Rotor under rotating and parked conditions, a vortex line method using a prescribed wake, and a parallelized coupled Navier-Stokes/vortex-panel solver (PCS). The linking of the spanwise distribution of bound circulation between both models enabled the quantification of three-dimensional effects with PCS. For the rotating turbine under fully attached flow conditions, the effects of the vortex sheet dissipation and replacement by a rolled-up vortex on the computed radial force coefficients were investigated. A quantitative analysis of both radial pumping and Coriolis effect, known as the Himmelskamp effect, was performed for viscous as well as in viscid flow. For the parked turbine, both models were applied at various pitch angles corresponding to fully attached as well as stalled flow. For partially stalled flow, computed results revealed a vortical structure trailing from the blades upper surface close to the 40% radial station. This trailing vortex was documented as a highly unsteady flow structure in an earlier detached eddy simulation by another group, however, it was not directly observed experimentally but only inferred. Computed results show very good agreement with measured wind tunnel data for the PCS model. Finally, a new method for extracting three-dimensional airfoil data is proposed that is particularly well suited for highly stalled flow conditions.

A Parallelized Coupled Navier-Stokes/Vortex-Panel Solver

A Navier-Stokes solver, CFX V5.6, is coupled with an in-house developed Vortex-Panel method for the numerical analysis of wind turbines. The Navier-Stokes zone is confined to the near-field around one wind turbine blade, the Vortex-Panel method models the entire vortex sheet of a two-bladed rotor and accounts for the far-field. This coupling methodology reduces both numerical diffusion and computational cost. The parallelized coupled solver (PCS) is applied to the NREL Phase VI rotor configuration under no-yaw conditions. Fully turbulent flow is assumed using the k-e and k-ω turbulence models. Results obtained are very encouraging for fully attached flow. For separated and partially stalled flow, results are in good agreement with experimental data. Discrepancies observed between the turbulence models are attributed to different prediction of the onset of separation. This is revealed by two-dimensional (2D) results of the S809 airfoil.

Low Speed Design and Analysis of Wing/Winglet Combinations Including Viscous Effects

The design and analysis of winglets is presented from an aerodynamic point of view. The winglets considered are small fences placed upward at the tip of the wing to improve the wing efficiency by decreasing the induced drag for a given lift. Viscous corrections are accounted for by using a two-dimensional viscous polar, with the assumption that at design conditions the flow is fully attached. The comparison of the inviscid and viscous designs indicates that viscosity has little effect on the optimum geometry. In the presence of viscous drag, the winglets produce a small thrust; due to viscosity, the overall efficiency gain is decreased. The effect of a small yaw angle on a wing equipped with such optimal winglets indicates that, even in the presence of viscous effects, they provide weathercock stability.

ANALYSIS AND DESIGN OF WINGS AND WING/WINGLET COMBINATIONS AT LOW SPEEDS

Numerical treatment in Prandtl lifting-line theory of the nonlinearity associated with a 2-D lift curve, when the local incidence is larger than the incidence of maximum lift, is proposed. It is shown that the use of an artificial viscosity term makes the solution unique and allows the iterative method to converge to a physically meaningful solution, that is in agreement with the exact solution for the test case. The design and analysis of winglets is presented. The winglets considered are small fences placed upward at the tip of the wing to improve the wing efficiency by decreasing the induced drag. The effect of yaw on a wing equipped with such optimal winglets indicates that they provide weathercock stability.

Application of a 'Parallelized Coupled Navier -Stokes/Vortex - Panel Solver' to the NREL Phase VI Rotor

A commercially available Navier -Stokes solver, CFX V5.6, is coupled with an in -house developed Vortex -Panel method for the numerical analysis of wind turbines. The Navier Stokes zone is confined to the near -field around one wind turbine blade, the Vortex -Panel method models the entire vortex s heet of a two -bladed rotor and accounts for the far -field. This coup ling methodology reduces both numerical diffusion and computational cost. The coupled solver is parallelized on a cluster of 4 processors. The parallelized coupled solver (PCS) is applied to some distinctive cases of the NREL Phase VI rotor configuration with and without flow separation under steady and no -yaw conditions. Fully turbulent flow is assumed using the k -� and k -� turbulence models. Calculations performed with the coupled solver show very good agreement with experiments for fully attached flow. For separated and partially stalled flow, the k -� model overpredicts rotor power while the k -� model still shows better agreement with experiments. Discrepancies between the two turbulence models are related to different prediction of the onset of separation. This is revealed by 2D airfoil data of the S809 profile.

Finite element calculation of steady transonic flow in nozzles using primary variables

Steady irrotational-isentropic flow of perfect fluid in a plane converging-diverging nozzle is modelled using a system of two first order partial differential equations in the primary variables. A least square/formulation transforms the first-order system into an equivalent second-order system well adapted to discretization methods and allowing the use of powerful iteration algorithms such as conjugate gradient or Newtons method which yield fast convergence. The other advantage of this variational approach is the direct applicability of the finite element method which is more accurate in this case than the corresponding finite difference method.

A CONSERVATIVE BOX-SCHEME FOR THE EULER EQUATIONS

The work presented in this paper shows that the mixed-type scheme of Murman and Cole, originally developed for a scalar equation, can be extended to systems of conservation laws. A characteristic scheme for the equations of gas dynamics is introduced that has a close connection to a four operator scheme for the Burgers-Hopf equation. The results indicate that the scheme performs well on the classical test cases. The scheme has no tuning parameters and can be interpreted as the projection of an L∞-stable scheme. At steady state second order accuracy is obtained as a by-product of the box-scheme feature

Finite element least square method for solving full steady Euler equations in a plane nozzle

A finite element least square method is applied to the steady Euler equations in a nozzle or a channel. For the capture of shock waves an artificial density formula is used. Fast convergence is achieved with I.C.C.G. algorithm.