This paper concerns an experimental investigation, conducted to estimate the aerodynamic effects of aircraft battle-damage repair patches. Of particular concern in this study are the wings. Three different repair schemes are considered, lower (repair at the intrados), upper (repair at the extrados) and full repairs (both intrados and extrados at the same time). Preliminary results clearly showed that repair patches improve the aerodynamic performances of the damaged aircraft model. The full repair was shown to achieve the best recovery of the aerodynamic performances provided that the patch is thin enough. Repairs performed on only one surface (i.e. upper or lower) were also shown to provide significant aerodynamic improvements. The improvement tendency decreases with the increase of the patch thickness. Above a certain thickness value, the fineness decreases below the fineness of the damaged unrepaired model.
The aim of this study is to find the most adequate numerical model to simulate the aerodynamics of the helicopter rotor in hovering flight, using CFD code Fluent. In this work, the Caradonna and Tung blades are used with NACA0012 profile and an aspect ratio of six. The rotating rotor is modeled by the multiple references rotating frame method (MRF). Using the periodicity condition, computations are carried only on one blade. For grid generation, the structured mesh is generated near the wall region with 30 300 y and for the rest of the computational domain, the unstructured mesh is used. The value of the near-wall resolution y p depends on the value of the mean skin friction coefficient. f C According to the study of Lombardi et al. (Numerical Evaluation of Airfol Friction Drag. Journal of Aircraft, 2000), the value of f C can be considered similar for both flat plat and NACA0012 airfoil. To evaluate the surface pressure distributions, we have treated the effect of the collective pitch angle (θ), the tip Mach number (M tip) and the two turbulence models, standard k and Spalart-Allmaras. The obtained results are expressed in terms of pressure coefficient C p , have been validated by comparisons with the experimental data. In addition, we discuss in this study the prediction of shock location on the upper surface of the blade.
The flow around a NACA 64 1 -412 airfoil with circle damage is numerically investigated using the Ansys Fluent package. Several diameter values are considered for the damage which is located at either quarter or mid chord. The numerical domain is covered with a multiblock structured hexagonal grid consisting of 344,680 cells in the undamaged case and 351,540 cells in the damaged case. Inside the damage hole, a structured tetragonal mesh is used. Turbulence effects are taken into account via the k- model. The results show that the presence of the damage hole decreases the lift coefficient and increases the drag coefficient, resulting in a loss of airfoil performance (fineness decrease). The numerical simulations show that the flow through the damage corresponds either to a weak or a strong jet. In the first case an attached wake forms giving the smallest change in the force coefficients whereas the second case shows a separated wake with a reverse flow giving the highest force coefficient change. The present paper also compares the structure of the damage through flow with previously published experimental results. Finally, the numerical solution is qualitatively and quantitatively validated using available experimental results.
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