Geometry cleanup WindTunnel set up and CFD Simulation of a Formula FSAE car for two different racing conditions Lot of turns and straight using converge studio and paraview

Geometry cleanup WindTunnel set up and CFD Simulation of a Formula FSAE car for two different racing conditions ( Lot of turns and straight) using converge studio and paraview

The main objective of this project is to perform geometry clean up, boundary flagging, virtual wind tunnel, pre-processing, CFD simulation and Post-processing of a formula FSAE car. The project has been divided into two phases

PHASE 1: - GEOMETRY CLEANUP

• Cleanup the 48 errors
• Flag the front wings, rear wings, tyres, suspension links as separate boundaries
• Create a virtual wind tunnel
• Ground plane reference is provided in the lower end of the tyres. There will be a \"flat section\" in all the 4 tyres. This refers to the location of the ground plane. You will have to create the ground plane and perfectly merge it with the tyres.
• Run a virtual wind tunnel no-hydro test and a coarse simulation test to prove that you have finished face 1 correctly.
• For phase-1, the virtual wind tunnel boundary conditions and physical models can be assumed.

PHASE 2 - Detailed Setup

Aero Simulations for their FSAE vehicle and they have hired you to do the job. The suspension team wants a detailed report on the total downforce on individual components. They have two races in this upcoming season.

Race details are as follows

Race-1

• Racing track conditions - Lot of turns
• Average lap speeds - 45kmph
• 70% turns at 45 degrees
• 20% turns at 80 degrees
• 10% turns at 20 degrees

Race-2

• Racing track conditions - Straights
• Average lap speed - 75kmph

INTRODUCTION:

Formula SAE is a student design competition organized by SAE International (previously known as the Society of Automotive Engineers, SAE). The concept behind Formula SAE is that a fictional manufacturing company has contracted a student design team to develop a small Formula style race car. The prototype race car is to be evaluated for its potential as a production item. Each student team designs builds and tests a prototype based on a series of rules, whose purpose is both ensuring on-track safety (the cars are driven by the students themselves).

Engine

The engine must be a four-stroke, otto cycle piston engine.

Suspension

The suspension is unrestricted save for safety regulations.

Aerodynamics

There are few regulations or requirements on aerodynamics and design judging tends to frown upon aerodynamic parts that do not have definite test data, usually in the form of wind tunnel testing or at least CFD analysis. Therefore, most cars that do utilize aerodynamic downforce tend to develop their entire car around the aerodynamic package, including massive wings and undertray. Thus helps to improve vehicle performance.

Weight

There is no weight restriction. The weight of the average competitive Formula SAE car is usually less than 440 lb (200 kg) in race trim.

In general, with the help of the venturi effect, it creates two pressure zones high and low using the aerodynamic phenomenon. Then the pressure difference created between the higher pressure flow over the body and also the low-pressure zone below the body created net downforce.

The study on FSAE car is to perform CFD simulations for an ABCD racing company which needs the data of the downforce by using the following software namely, Converge, Cygwin, and for post-processing ParaView. With the help of this data, this team can able to change designs, tyres, the centre of gravity and suspension spring stiffness. For testing, we are using two tracks the first track can be varying turns which can help us to find tyre working in friction and for second track straight which focus on drag reduction.

PHASE 1: - GEOMETRY CLEANUP

SURFACE CLEAN UP:

A diagnosis was run on FSAE (STL FILE ) to check the errors. First, it shows the nonmanifold problems this comes because a single edge is shared by more than one triangle. By using the delete and patch tool I resolved this error. The clean geometry is posted below for the reference.

BOUNDARY FLAGGING:

The next step will be flagging the appropriate boundaries of the car. For this flagging, the tool known as the fence is used. The rear wing was first flagged here a shortcut named control+E is used for selecting the appropriate triangles for flagging. Likewise, I have to follow this fencing method for other components except for underbody and suspension because here I have used the angle selection method. In addition to the suspension, I have followed extra procedure first I have to create a boundary and then clean up after that I have created a fence using the existing the boundaries. This completed the second portion of the phase.

VIRTUAL WIND TUNNEL SET UP:

For setting up a wind tunnel there was a lot of factors to be considered. The first thing is inlet space should be always less than the outlet boundary space. Then the wake region should not interpret with the outlet flow show outlet boundary should be extended. In the beginning, inflow should be uniform so the car should be placed correctly in the wind tunnel. The width should be equally distributed along both sides of the car. Then height should be kept according to the car length. The respective dimensions inlet to the front of the car is 2.5 m and outlet to the rear of the car is 27.5 m and height and width will be 2.5 m and 5 m. For wind tunnel to a lot of turns, I have to change the direction using the transformation tool and the degree value is 49%.

STRAIGHT TRACK

LOT OF TURNS

PHASE 2: CASE SET UP FOR PRE PROCESSING

BOUNDARY CONDITIONS:

General flow

RUN PARAMETERS:

Transient solver with full hydrodynamic mode was chosen

SIMULATION TIME PARAMETERS:

The end time was calculated using the flow-through time formula for a lot of turns track the value is 5.2s. For the straight track, the value is around 1.56s.

NOTE: (2 times greater than flow through time )

REGIONS AND INITIALIZATION:

The region created here is named as Region 0. The inlet velocity is the same as inlet flow velocity.

oxygen with a concentration of 0.23

nitrogen with a concentration of 0.77

Temperature- 300K,

Pressure- 101325 Pascal

If we specified velocity in regions will take a shorter time to compute the simulation process.

TURBULENCE MODEL:

For this project, I have chosen standard k-ω 2006 because it solves two transport equations to resolve Reynolds stress tensor. Also, it addresses some additional issues namely poor predictions of swirling and rotating flows. It has an automatic enhanced wall treatment function. For this case the Y+ value should be 0.5 -300 otherwise it goes below 10 or 1 it will use enhanced wall treatment.

GRID CONTROL:

The base grid sizes are calculated using the below-Mentioned terms free stream velocity, density, characteristic length, dynamic viscosity, and desired (Y+).

Website name: http://www.pointwise.com/yplus/. The following equations are also used to finding the wall spacing value:

1. Reynolds Number:

Reynolds number is a dimensionless value which is applied in fluid mechanics to represent whether the fluid flow in a duct or pat a body is steady or turbulent. This value is obtained by comparing the inertial force with the viscous force.

Reynolds number is given by,

Reynolds Number = Inertial Force / Viscous Force

The Reynolds number formula is expressed by,

where:

• ρ is the density of the fluid ( kg/m³)
• u is the velocity of the fluid concerning the object (m/s)
• L is a characteristic linear dimension (m)
• μ is the dynamic viscosity of the fluid (Pa·s or N·s/m² or kg/m·s)
• ν is the kinematic viscosity of the fluid (m²/s).

The Kind of flow is based on the value of Re

1. If Re < 2000, the flow is called Laminar
2. If Re > 4000, the flow is called turbulent
3. If 2000 < Re < 4000, the flow is called transition.

2.SKIN FRICTION COEFFICIENT:

3. WALL SHEAR STRESS:

The wall shear stress is given by:

`τ_ω = (C_f.ρ.V^2)/2`

Where is the dynamic viscosity, is the flow velocity parallel to the wall and is the distance to the wall.

The SI unit of wall shear stress is pascal ().

4.FRICTION VELOCITY:

5.WALL SPACING:

A non-dimensional wall distance for a wall-bounded flow can be defined in the following way:

Where is the friction velocity at the nearest wall, is the distance to the nearest wall and is the local kinematic viscosity of the fluid.

is often referred to simply as y plus and is commonly used in boundary layer theory and in defining the law of the wall.

Based on these calculations, wall spacing value is found to be of straight track case and for a lot of turns case. Also if I use this fine mesh size simulation running will take indefinite time to achieve. So I used this mesh sizes for

The waking region is characterized by very low pressure and less drag. So larger the wake region and trailing edge of the car will face less drag.

FSAE LOT OF TURNS:

Mesh:

Y- Plus :

Fig 1. The upper side of the car

Fig 2. The downside of the car

Video 1. Y PLUS animation

VELOCITY CONTOUR:

Fig 1. Velocity profile

Fig 2. Velocity profile ( Streamline )

Video 1. Velocity streamline animation

Video 2. Velocity animation

VORTICITY :

Fig 1. Upperside of the car

Fig 2. The downside of the car

FIG 3. SIDE VIEW OF THE CAR

Video 1. Vorticity animation

VORTICITY STREAMLINE :

FLOW VISUALIZATION OVER FRONT AND REAR WINGS, WHEELS

FRONT WINGS

REAR WINGS

WHEELS

UNDERBODY AND UPPER BODY:

FLOOR:

FSAE STRAIGHT TRACK:

Y- Plus :

Y-PLUS

Video 1. Y PLUS animation

VELOCITY CONTOUR:

Fig 1. Velocity profile

Fig 1. Velocity profile underbody

Video 2. Velocity animation

Pressure:

Fig 2. Pressure profile

Video 2. Pressure animation

VORTICITY :

Fig 1. Upperside of the car

Fig 2. Down side of the car

Video 1. Vorticity animation ( Cut)

Fig 3 . Vorticity ( cut section)

LIFT:

Fig 1. Lift

Video 1. Lift animation

DRAG:

Fig 1. Drag

Fig 1. Drag ( Under body)

Video 1. Drag animation

A LOT OF TURNS:

COMPONENT NAME	LIFT FORCE (N)	DRAG FORCE (N)
BODY	115900	-4300
REAR WING	-124	0.9
FRONT WHEELS	2295	1.3
REAR WHEELS	3125	8
FRONT WING RIGHT	-145	-14
FRONT WING LEFT	-125	-12
FRONT SUSPENSION RIGHT	-8.4	-0.7
FRONT SUSPENSION LEFT	-8.5	-0.5
REAR SUSPENSION RIGHT	-1.2	-9.5
REAR SUSPENSION LEFT	-1.7	-3.5
FLOOR	-119800	3940
HUMAN	3668	-0.25

STRAIGHT TRACK:

COMPONENT NAME	LIFT FORCE (N)	DRAG FORCE (N)
BODY	-108235	3900
REAR WING	-113	0.7
FRONT WHEELS	2145	1.2
REAR WHEELS	3115	7.3
FRONT WING RIGHT	-126	-12
FRONT WING LEFT	-113	-11.5
FRONT SUSPENSION RIGHT	-8.2	-0.6
FRONT SUSPENSION LEFT	-7.95	-0.43
REAR SUSPENSION RIGHT	-2.3	-8.7
REAR SUSPENSION LEFT	-1.7	-3.2
FLOOR	-113840	3730
HUMAN	3468	-0.24

RESULTS:

The car body generates a large amount of lift force it\'s very important in opposite the front and rear wings generate low amount if lift force. So we have to change the angle of attack or airfoil configuration. Indeed, Car body generates more amount of drag and floor ( underbody ) generates less drag. So the higher pressure acts on the top surface and lowers pressure acts on the down surface (Lot of turns). so the car has a good hood.

Wakes a body moving through the air create the distributed flow region. In the wake region, free stream velocity is zero so it forms a momentum loss which is known as form drag Coming to Form Drag (Or Pressure Drag), as the name suggests, it is due to the Form (shape of the body). As the fluid moves relative to the body, two forces come into play. The body is tending to slow the fluid because of shear friction force, on the other hand, the fluid inertia is trying to push the flow over the body. At some point over the surface of the body, the viscous forces overcome the inertial force and the fluids separate from the body. The separated fluid moves away from the body, which creates a region behind the body, where the fluid pressure is low. This region is called the wake region. Now the body is subjected to a pressure differential in the flow, in front of it is the fluid with high pressure and behind it, the fluid with low pressure. (Lot of turns)

The car body was rotated at an angle of 48.03 degree which is a side slip angle and the tire experiences more load because of turning and high-velocity region in the nose and the air ducts then the low-pressure region in the flow separation region streamline visualization will create drag in turn both combine to produce lift. ( Lot of turns)

The flow over wheels where the top surface of the wheel experiences the higher velocity because the flow over there creates the more lift. the flow front wings where high pressure on top and low pressure on the bottom. The two endplates are fixed to prevent the formation vortices here the vortices are seen at the end so additional drag increases. To reduce the drag is to reduce the airfoil thickness and adding flaps like in an aeroplane.

The flow over the rear wing as seen that it creates lift force over the corners by seeing the velocity profiles. This because of the generation vortices and the airfoil in the car wing usually have low aspect ratio and in turn, it creates the drag behind the body and also reduces the angle of attack of free stream air. To improve the lift is to increase airfoil thickness and also increase the height of endplate. The Y plus is uniform throughout the body. The forces on the suspension links are very low there is a need in change of suspension.