SIMULATION OF A MANEUVERING AIRCRAFT USING A PANEL METHOD

We present a method for numerical simulations of a maneuvering aircraft, which uses a first-order unsteady panel method as the only source of aerodynamic forces and moments. By using the proposed method, it is possible to simulate a motion of an aircraft, while the only required inputs are geometry and inertia characteristics, which significantly reduces the time required to start the simulation. We validated the method by a comparison of recordings of flight parameters (position, velocities, accelerations) from an actual aerobatic flight of a glider and the results obtained from the simulations. The simulation was controlled by deflections of control surfaces recorded during the actual flight. We found a reasonable agreement between the experimental data and the simulation. The design of our method allows to evaluate not only the integral kinematic quantities but also instant local pressure and inertia loads. This makes our method useful also for a load evaluation of an aircraft. A significant advantage of the proposed method is that only an ordinary workstation computer is requiredto perform the simulation.

Assessment of Surface-Based Aeroacoustic Noise From Blades of a Vertical-Axis Wind Turbine

Surface-based sources of aerodynamically-generated noise for the 17-m troposkien shape vertical-axis wind turbine are predicted using Farassat’s Formulation 1A of the Ffowcs Williams-Hawkings equation. By discretizing the three-dimensional turbine blades over the height of the turbine into constant-radius sections, the blades were aerodynamically modeled in two-dimensions in the horizontal plane by an unsteady panel method to obtain results for surface pressures and velocities. The acoustic pressure generated by the blades throughout their rotations was determined by the combination of loading and thickness noise sources on the surface of the blade sections in the time-domain. The simulation results were compared to experimental results for the acoustic pressure power spectral density. The sound pressure level around the turbine was found to have a slight dipole radiation pattern, caused primarily by the loading acoustic pressure on the blades.

NREL Phase VI Wind Turbine Modeling Using an Unsteady Panel Method

Wind energy production has been increasing steadily in the past decade. The majority of wind power is generated by horizontal axis wind turbines (HAWT). We investigate the modeling of the HAWT using the vortex panel method, which is an inviscid, steady, computationally inexpensive method. Pressure coefficient profiles, calculated by the vortex panel method, were compared to NREL phase VI wind turbine experiments under two different flow conditions. We show that if the flow is not separated over the blade, the vortex panel method can capture the pressure profile on the blade. Furthermore, the panel method has been extended to handle unsteady inviscid flows to investigate the effect of blade oscillations on the power generation, which is not known. The unsteady behavior is modeled by accounting for the time rate of change of circulation. Unsteady effects due to heaving and pitching motion were quantified for different blade oscillation frequencies. It is estimated that the mean thrust coefficient with heaving and pitching motion can be higher than the thrust generated without blade motion in some cases assuming that the flow does not separate.

Simple and efficient numerical tools for the analysis of parachutes

Purpose – The purpose of this paper is to describe a set of simple yet effective, numerical method for the design and evaluation of parachute-payload system. The developments include a coupled fluid-structural solver for unsteady simulations of ram-air type parachutes. The main features of the computational tools are described and several numerical examples are provided to illustrate the performance and capabilities of the technique. Design/methodology/approach – For an efficient solution of the aerodynamic problem, an unsteady panel method has been chosen exploiting the fact that large areas of separated flow are not expected under nominal flight conditions of ram-air parachutes. A dynamic explicit finite element solver is used for the structure. This approach yields a robust solution even when highly nonlinear effects due to large displacements and material response are present. The numerical results show considerable accuracy and robustness. Findings – A simple and effective numerical tool for the analysis of parachutes has been developed. Originality/value – An analysis code has been developed which addresses the needs of ram-air parachute designers. The software delivers reasonably accurate results in a short time using modest hardware. It can therefore assist the design process, which nowadays relies on empirical methods.

An Analytical–Numerical Aerodynamic Formulation for Efficient Aeroacoustics Analysis of Rotorcraft

This paper presents an analytical-numerical aerodynamic/aeroacoustic formulation for the analysis of the tonal noise emitted by helicopter rotors and propellers. It is particularly suited for those configurations dominated by local high-frequency changes (both in time and space) of blades inflow velocity. The solution of the Ffowcs Williams-Hawkings equation for noise radiation prediction is combined with the frequency-domain Küssner-Schwarz formulation that yields the sectional, unsteady aerodynamic loads, starting from the knowledge of the downwash on the airfoil due to blade motion and inflow induced on it by any external source of perturbation. Here, the blade inflow is assumed to be evaluated through a 3D, unsteady, panel method formulation suited for the analysis of rotors operating in a complex aerodynamic environment. This aerodynamic/aeroacoustic model gives a computationally efficient solution procedure that may be conveniently applied in preliminary design/multidisciplinary optimization applications. The proposed approach is validated through comparison with the (accurate, but computationally expensive) acoustic field obtained through the blade pressure loads directly evaluated by the time-marching panel-method solver. The results are provided in terms of blade loads, noise signatures and sound pressure level contours.