Spoiler Effect on a Car Aerodynamics, ANSYS Fluent CFD Simulation Training

66.67 

In this project, a car in two modes of with and without spoiler in terms of aerodynamic coefficients, in 3 different speeds, has been studied using ANSY Fluent software.

This product includes Geometry & Mesh file and a comprehensive Training Movie.

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Description

Problem definition and simulation strategy (Spoiler)

In this project, the car’s geometry in two modes of with and without spoiler in terms of aerodynamic coefficients, in 3 different speeds with zero side angle, has been studied by ANSYS Fluent software. The considered speeds are 22, 46, and 70 meters per second (m/s), and at the highest speed, the stability of the car in the case which a spoiler has been added, is examined.

Introduction

In the dynamic simulation, quasi-experimental aerodynamic coefficients are used. These coefficients are obtained by quasi-experimental software. The coefficients obtained in these softwares have many errors. To achieve more accurate coefficients, numerical simulation by computational fluid dynamics is used, and the coefficients obtained by semi-experimental simulation software are calibrated using CFD coefficients. In this research, the calculation of aerodynamic coefficients has been done using numerical simulations and Fluent commercial software.

Car and Spoiler Geometry

In this section, the geometry of the desired car in two modes of with and without spoiler is discussed. The spoiler is located at the rear of the car.

spoiler

Because in the subsonic stream, the flow information also affects the upstream, the solution domain is selected as follows. In Downstream, the vortex shedding behind the geometry to achieve the appropriate residuals in solving the larger solution domain is considered.

spoiler

The following figure shows the coordinate axes.

spoiler

Mesh

One of the most influential and time-consuming steps in numerical simulations, is grid generation. The better mesh quality, make other solving steps to proceed more accurately.

Due to the dimensions of the problem and the car’s geometry, the prism grid has been used for the boundary layer, and the unstructured grid has been used for other parts of the solution domain. To generate a mesh in ICEM software, you must first determine the size of the mesh elements in different parts according to the dimensions of the problem and the type of flow and geometry of the object under study.

Various methods have been proposed to create an unstructured mesh in ICEM software. This software has two top-down and bottom-up methods for generating a UNS mesh. These two methods are introduced below.

To create a suitable mesh, the combined (hybrid) method is used so that the whole solution domain, including surfaces and lines, is meshed with the help of the Octree method. Then with the help of the Delaunay method and with the help of the existing mesh, a smooth mesh is created in the whole solution domain.

The following figure shows the grid on the middle page:

spoiler

The mesh in parts of the geometry where the radius changes suddenly and on the fractures is fine, and it is larger in other areas.

Solution Settings

We investigate the issue numerically, using Fluent commercial software, and solve this problem in Steady mode using the pressure-base method. Also, we use Fluent software to solve the governing equations numerically. In this chapter, we consider flow conditions, type of boundaries, type of solvent, and flow discretization methods.

Fluid Properties

In this research, the air has been used as a fluid. The following table shows the air properties extracted from the Fluent software database, given that the current is in an incompressible regime and its density is constant.

Amount (units) Fluid Properties(air)
1006.43 (J/kg.K) Thermal pressure coefficient
0.0242(w/m.k) Thermal conductivity

Boundary Conditions

One of the most influential variables in the numerical solution process is boundary conditions. For this purpose, we use different boundary conditions in the computational range. We introduce these conditions as:

  • wall
  • velocity inlet
  •  pressure outlet
models (car)
K&W viscous model
SST K&W model
boundary conditions (car) (spoiler)
velocity inlet inlet
22 & 46 & 70 velocity magnitude (m/s)
pressure outlet outlet
0 Pascal gauge pressure
wall wall of body
stationary wall wall motion
solution methods (car
couple pressure velocity coupling
second order pressure spatial discretization
second order upwind momentum
first order upwind turbulent kinetic energy
first order upwind turbulent dissipation rate
initialization (car) (spoiler)
standard initialization method
0 (Pa) gauge pressure
22 & 46 & 70 (m/s) x-velocity
0 (m/s) y-velocity , z-velocity

Convergence

In computational fluid dynamics, We use iterative solutions to achieve the answer to the problem. These iterative solutions start by taking the initial values ​​and continue solving until they reach the convergence criterion or the number of steps specified by the user. We define different criteria for the convergence of the problem. One of the most widely used criteria for determining the convergence of a problem is residual values. Residuals are the sum of the values ​​calculated on all cells in the current and previous time steps. They are calculated in each iteration, and the solution continues until its value is less than the criterion specified by the user. It is usually recommended to reduce the residual values ​​by 3 or 4 orders. We can see in the figure below, all residuals, including velocities and parameters of the perturbation model, are smaller than 10e-3.

Spoiler

Examining the status of the results during the iterative solution and the residuals reaching the convergence criterion can help decide whether the solution converges. According to the problem, the convergence process of the drag force has been studied to ensure the convergence of the problem. The non-noticeable change in the desired quantity indicates the convergence of the numerical solution.

spoiler

Results (Spoiler)

In this chapter, we present and analyze the simulation results in two parts, qualitative and quantitative. The quality of the flow around the body has been studied using contour. The flow is also quantified using aerodynamic force values.

The following tables show the aerodynamic forces in two directions for two modes of with and without spoiler. Speed ​​is in meters per second, and forces are Newtons.

no spoiler
Velocity fx fz
22 145 -47
46 629 -250
70 1467 -527

 

with spoiler
velocity fx fz
22 184 -243
46 796 -1135
70 1847 -2633

spoilerspoiler

We can see from the diagrams and tables above, the drag force increases for the mode with the spoiler. As expected, the lift force increases in the direction that the body sticks to the ground, so the car’s stability increases, which causes control at high speeds of the car gets better.

You can obtain Geometry & Mesh file and a comprehensive Training Movie that presents how to solve the problem and extract all desired results.

2 reviews for Spoiler Effect on a Car Aerodynamics, ANSYS Fluent CFD Simulation Training

  1. William

    Thank you for sharing this project.
    Why did you use multiple inlets instead of one inlet and symmetry boundary conditions in the setup?

  2. Cameron M.

    Can we do the meshing of this project in ANSYS meshing?

    • melika maysoori

      Yes, why not? 😉 Both of these software’s are for creating the computational grid and both have very high accuracy in creating an optimal mesh. Incidentally, using Ansys Mashing software to create Unstructured mesh is more convenient and easier than ICEM CFD. In fact, ICEM CFD software is mostly used to create the structured mesh. But considering that many of our projects have been done with Ansys Mashing software, in order to be able to explain the tips of ICEM CFD to those who are interested, we have generated mesh on some products with this software. In fact, working with either software depends on your skill and your goal of the simulation. 🙂

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