M. Morelli

Analysis of Some Interference Effects in a Transonic Wind Tunnel

The effects of the walls of a test section on a model in transonic flow were investigated by using the AGARD Calibration Model B. Tests were carried out in a closed-circuit pressurized tunnel, with a confined square test section of 1.5 m width, with tapered slots giving a 5% porosity. Two models with different dimensions were used, with 0.85 and 0.056% blockage ratios. Longitudinal aerodynamic characteristics were analyzed by means of measurements performed at varying angles of attack (up to 24 deg) and Mach numbers from 0.3 to 1.2. In some flow conditions wall interference effects were probably present. However, the forces and moments dependent on the pressure distribution were likely to be related to the same factors, and therefore, the above effects tended to disappear when longitudinal stability and lift-dependent drag were analyzed as a function of lift characteristics. The drag rise Mach number evaluation seems be fully free from blockage effects. The dimensions of the tested larger model can be considered to be the largest reasonable ones for industrial applications, but, probably, not sufficiently small when high accuracy is required.

Appraisal of Numerical Methods in Predicting the Aerodynamics of Forward-Swept Wings

The capabilities of different numerical methods in evaluating the aerodynamic characteristics of a forward-swept wing in subsonic and transonic e ow are analyzed. The numerical results, obtained by means of potential, Euler, and Navier ‐Stokes solvers, are compared with experimental data. In particular, attention is focused on the aerodynamic quantities related to pressure distributions. Moreover, an attempt is made to investigate the capability of a Navier ‐Stokes solver to predict separation lines; both laminar Navier‐Stokes equations and Reynolds-averaged equations with a k-« model are considered. This analysis is carried out by comparing the numerical velocity e eld to the experimental visualizations, obtained through liquid crystals. All of the numerical solvers give results consistent with the physical limits of the equations that they discretized.

Correction of Wall Interference in Wind Tunnels: a Numerical Investigation

A procedure is described for the correction of wind-tunnel wall interference effects on the experimental measurement of aerodynamic coefficients. The correction is given by the difference between the values obtained in two different numerical simulations: In the first one the flow over the model in free-air conditions is simulated, whereas in the second one, the measured pressure values over the wind tunnel walls are used as boundary conditions. A necessary preliminarly step is the choice of the number, location, and accuracy of the pressure measurements. A strategy is proposed to determine these parameters, based on the same correction procedure in which the experimental part is replaced by numerical simulation. This strategy is applied to the subsonic flow around a complete aircraft configuration by means of a potential flow solver. The sensitivity to the number and location of sensors, as well as to the transducer accuracy, is investigated. Given the desired correction accuracy, the proposed strategy permits identification of suitable configurations with reduced time and computational costs