Aerodynamics of variable geometry wing/body combinations

Ostadsaffari, A

Abstract

A description of the experimental investigation of the aerodynamic characteristics of variable geometry of an aircraft model is presented. Aerodynamically, the model is tested-for a sweep range of 0°,12.5° 32.5°, and 52.5° and incidence range of 0° to 200° in 4° intervals. All the pressure distributions on the wing, glove, and body are recorded for each wind tunnel test. Aerodynamic forces and moments were also taken through a balance mechanism system which is attached to the model. This is connected to an independent computer terminal and a Teletype printer. Initially, a flow visualization to test the flow separation on the wing model was carried out.

A three-dimensional subsonic program, which was already developed by Hawker Siddeley Aviation Limited, was modified for our purposes in order to carry out numerical calculation of the aerodynamic characteristics and investigate the interference of wing and body. This programme has also been developed to include the compressibility effects and compare these results with those for incompressible flow. The three-dimensional numerical solution was a Panel method for the subsonic case. This investigates the three-dimensional flow-field using a distribution of quadrilateral vortex panels, the effects of which are summed to calculate the aerodynamic characteristics of the model.

This subsonic theory was applied to calculate the characteristics of the wind tunnel model over a similar range of sweep and incidence to those tested, for Mach numbers of 0 and 0.5. As the only input data required is the configuration geometry and the flight condition, however, the program can be used to calculate the aerodynamics of any wing-body arrangement specified by the user. The program includes the capability of analysing both fixed-wing and variable sweep-wing configurations. This computational method is capable of being applied to general arbitrary subsonic three-dimensional potential flows, including inlet flow fields. In panel methods, the velocity potential at any point in a flow field is expressed in terms of the induced effects of source and doublet (or vortex) sheet distributed on the boundary surfaces. The configuration surfaces are divided into panels, and essentially, this is a general three-dimensional boundary value problem solver that is capable of being applied to most problems that can be modelled within the limitations of potential flow. Compressibility effects are approximated by the Göthert rule.

Comparisons were made between the subsonic calculations and the experimental results and some other theoretical results. Hence, an indication of agreement and accuracy among them is seen, which is good up to a certain degree of incidence (about 10°). Owing to viscous effects, the experimental results for lift coefficient show a significant decline in size with respect to subsonic calculated results. Wing-body interference was calculated for subsonic flows and found to be favourable.

Similarly, a general supersonic program was developed for numerical analysis of the aerodynamic characteristics of a thin wing. The theory was extended to include wing-body interferences. This extended treatment consists of slender body theory combined with a thin wing solution using a "characteristic box" method for supersonic analysis. Streamwise pressure-distributions on an aircraft wing are presented, and also-some aerodynamic force and moment coefficients of this wing are-presented.

Finally, for wing body interaction analysis, the Nielsen method was used. All the relevant computations including centre of pressure position and interferences of wing and body for a combined model are presented. Comparisons of the supersonic results with some theoretical and experimental results shows good agreement. The interference calculations in this case showed favourable effects, which very broadly tend to be lower than those calculated for subsonic flow.

Citation

Ostadsaffari, A. Aerodynamics of variable geometry wing/body combinations. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Aug 19, 2009
• Publicly Available Date: Aug 19, 2009
• Keywords: Aerodynamics, Geometry, Aircraft
• Award Date: Oct 1, 1983