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On the application of CFD and MDO to aircraft wingboxes using commercial software
Published in Alphose Zingoni, Current Perspectives and New Directions in Mechanics, Modelling and Design of Structural Systems, 2022
ANSYS Fluent was chosen to be the CFD solver, and ANSYS Mechanical was chosen to be the FEM solver. The CFD program solves the Reynolds-Averaged Navier-Stokes Equation with the SST k-omega turbulence model. Air was the working fluid and was modeled as an ideal gas at the operating conditions of a 747-400. Air enters the fluid domain using a velocity inlet boundary condition at 255m/s and exits the domain with a pressure outlet boundary condition. All plane surfaces are set with the no-slip boundary condition. From the CFD analysis, the lift and drag coefficients are obtained, as well as the pressure acting on the surface of the wing. The pressure can then be mapped onto the FEM mesh which is done through ANSYS Workbench. One major benefit of using ANSYS Workbench is that it does not require the data to be processed by an external program which decreases computation time and ensures better accuracy of the mapping. Once the pressure has been mapped onto the aircraft wing, ANSYS Mechanical can then calculate the Von Mises stress to be used for the constraints of the optimization.
Comparison between empirical and CFD based methods for ship resistance and power prediction
Published in C. Guedes Soares, T.A. Santos, Trends in Maritime Technology and Engineering Volume 1, 2022
H. Islam, M. Ventura, C. Guedes Soares, M. Tadros, H.S. Abdelwahab
For each hull model, a grid dependency study is performed using three mesh resolutions with a refinement ratio of roughly 1.25. The final resolution selected is around 3 million cells for all three cases, with a maximum y+ value of around 200. Detailed grid and time step dependency for the models have been previously discussed by Islam & Guedes Soares (2019b) and Islam & Guedes Soares (2021). The boundary conditions for the simulations are set following standard practices, as shown in the DTCHull tutorial in OpenFOAM, except that full hulls are simulated in this study. For turbulence modeling, the two-equation SST K-Omega turbulence model is used following the general practice in ship hydrodynamic studies. The initial turbulence parameters are calculated based on the Reynolds number, using common guidelines (Labanti et al., 2016) for turbulent simulations.
Effect of aspect ratio on the recirculation region of 35° Ahmed body
Published in Australian Journal of Mechanical Engineering, 2023
Naseeb Ahmed Siddiqui, Martin Agelin-Chaab
The present article seeks to study the effect of aspect ratio based on the length to the height. A total of five aspect ratios are considered for the investigation at a Reynolds number based on the height of the Ahmed body of 7.8 × 105. The flow governing equations are solved in the FLUENT solver using the SST K-Omega turbulence model. It reveals that the AR1, which has the minimum length, provides the maximum drag and lift coefficients. It is shown that the viscous force is proportional to the surface area and increases with the aspect ratio. The investigation also found that the reason for the higher pressure in the AR1 is the reattachment of the separated flow at the rear end, providing an increase in drag. It is supported by the horseshoe vortex formed at the vertical base. The critical insight of this investigation provides is that the relation between the recirculation region with the base drag might not be valid for the length to height-based aspect ratio, which are evident for other blunt bodies in the literature. Because no change in the aspect ratio of the recirculation region. Consequently, the results suggest that there must be a minimum aspect ratio for the Ahmed body that gives a higher drag. Similarly, a higher aspect ratio, after which the drag will begin to decrease is also predicted. However, the search for the exact aspect ratio is a future research project which can provide important insights to the designer while deciding the overall aspect ratio of commercial vehicles.