Computational Aeroacoustics

The objective of the multiphase flow simulation was to analyze the flow over a NACA 634-021 airfoil, of a clefted wing, (humpback whale), and compare the aerodynamics simulation results to the normal wing. We have also studied the effects of laminar separation bubble over the same airfoil so as to carry out an airfoil design optimization.

The CFD modeling and meshing have been done in Gambit using a rectangular domain, meshed with tetrahedral elements. A SIMPLE method has been used to determine the solution. Reynolds number= 2.05E6. The same has been exported to Fluent, where the FSI analysis of the flow has been carried out using the standard k-epsilon model.

Graphs base on the turbulence modeling for CFD have been plotted to compare coefficient of lift, the coefficient of drag and L/D ratios for both normal and clefted wings. Presence, location, variation, and effects of laminar separation bubble have been studied over a wide range of angles of attack, i.e., from 30deg to 50deg.

It has been concluded from the CAE consulting project that a clefted wing at an angle of attack 35deg, Reynolds number 2.05E6 must be considered for achieving maximum possible performance for the given airfoil.

Over the years as an engineering simulation consultancy, we have undertaken numerous computational fluid dynamics simulation projects involved in Aerodynamics simulation.

One such CFD analysis project was the quantification of the impact of leading edge geometry and its shape on boundary layer transition. For experimental wind tunnel testing as well as CFD simulations of the fluid-structure interaction, traditionally elliptical leading edges are being used on the flat plate. These leading edges have an aspect ratio of 12. However, to understand the physics of the CFD flow analysis as well as the fundamental flow structure of the boundary layer, it is essential to minimize the impact of the leading edge of the flow structure.

This computational fluid dynamics simulation project involved identifying the most aerodynamically efficient and easy to manufacture leading edge that could be used for experimental boundary layer transition studies.

The methodology in this fluid dynamic analysis case involved the 2D simulation of numerous elliptical leading edges ranging from aspect ratio 1 to aspect ratio 20. The transition onset locations of these leading edges were compared with a plate having an infinite leading edge (i.e. a flat plate with no thickness).

The mesh in this case for the CFD services was a structured multi-block mesh with mesh elements clustered around the leading edge. The mesh was generated using CFD simulation software in a manner to ensure that a y+=0.1 was maintained. Grid independence studies were conducted based on the mesh data provided in existing literature. Three meshes of 75k, 108k, and 200k mesh elements were used and the skin friction coefficient was the parameter based on which the independence fluid flow simulation study was conducted. In the present case, the mesh with 108k elements proved to provide the most accurate CFD Simulation result as compared to existing literature.

The turbulence model, in this case, was the Transition SST model incorporated in FLUENT. The fluid dynamics simulations were conducted using the steady state pressure-based solver and the simulations were allowed to converge to a residual value of 10^(-7).

Based on the computational fluid dynamics analysis simulation of multiple leading edges of different aspect ratios, it was found that the leading edge with aspect ratio 20 provides the least disturbance to the flow. From the FSI simulation disturbance to the flow increases with a reduction in aspect ratio.

However, manufacturing of an elliptical leading edge of aspect ratio 20 is not only difficult but also expensive. In order to attain a good compromise between accuracy and costs, we also simulated a wedge-shaped leading edge with the same length as the elliptical leading edge with aspect ratio 20. It was found that the wedge-shaped leading edge provides an optimum balance between accuracy and ease of manufacturing.

A paper-based CFD design based on the impact of the leading edge shapes has been published in the American Institute of Aeronautics and Astronautics (AIAA) journal and presented at an AIAA conference in 2015.

Besides the above aerodynamic simulation project, our CFD consultants also conducted multiphysics simulation projects to quantify the impact of blockages in the wind tunnel at our research facility.

Some of the fluid flow analysis projects include structural optimization of a 3D aircraft wing, the study of the impact of icing and extreme heat on the airfoil surface, a study of different turbulence models in FLUENT etc.