Challenge

Week 11: FSAE Car Project

AAnurag Bharadwaj29 Aug 2021

AIM

The aim is to simulate the Aerodynamics Behaviour of FSAE Car

OBJECTIVE

ABCD Racing company is looking to perform 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

FSAE CAR

The following are the rules for FSAE Car

Engine

The engine must be a four-stroke, Otto-cycle piston engine with a displacement no greater than 710cc. An air restrictor of circular cross-section must be fitted downstream of the throttle and upstream of any compressor, with a diameter no greater than 20mm for gasoline engines, forced induction or naturally aspirated, or 19mm for ethanol-fueled engines. The restrictor keeps power levels below 100 hp in the vast majority of FSAE cars. Most commonly, production four-cylinder 600cc sport bike engines are used due to their availability and displacement. However, there are many teams that use smaller V-twin and single-cylinder engines, mainly due to their weight-saving and packaging benefits. Very rarely do teams build an engine from scratch, few examples include Western Washington University's 554cc V8 entry in 2001, University of Melbourne's "WATTARD" engine in 2003–2004, and University of Auckland's V twin.

Suspension

The suspension is unrestricted save for safety regulations and the requirement to have 50mm total of wheel travel. Most teams opt for four-wheel independent suspension, almost universally double-wishbone. Active suspension is legal.

Aerodynamics

Complex aerodynamic packages, while not required to compete at competition are common among the fastest teams at competition. With the low speeds of the FSAE competition rarely exceeding 60 mph (97 km/h), designs must be thoroughly justified in the design judging event through wind tunnel testing, computational fluid dynamics, and on track testing. Aerodynamic devices are regulated through maximum size and powered aerodynamic devices are outlawed.

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. However, the lack of weight regulation combined with the somewhat fixed power ceiling encourages teams to adopt innovative weight-saving strategies, such as the use of composite materials, elaborate and expensive machining projects, and rapid prototyping. In 2009 the fuel economy portion of the endurance event was assigned 100 of the 400 endurance points, up from 50. This rules change has marked a trend in engine downsizing in an attempt to save weight and increase fuel economy. Several top-running teams have switched from high-powered four-cylinder cars to smaller, one- or two-cylinder engines which, though they usually make much less power, allow weight savings of 75 lb (34 kg) or more, and also provide much better fuel economy. If a lightweight single-cylinder car can keep a reasonable pace in the endurance race, it can often make up the points lost in overall time to the heavier, high-powered cars by an exceptional fuel economy score.

Example: At the 2009 Formula SAE West endurance event, third-place finishers Rochester Institute of Technology completed the endurance course in 22 minutes, 45 seconds with their four-cylinder car, while fourth-place finishers Oregon State University finished in 22 minutes, 47 seconds with their single-cylinder car; this gave RIT 290.6 of 300 points for the race portion of the event and OSU 289.2 points. However, OSU used the least fuel of any car (.671 US gal (2.54 l), or 20.3 mpg_‑US (0.116 l/km) over the entire endurance race) and received the full 100 points for fuel economy, while RIT used 1.163 US gal (4.40 l) (11.75 mpg_‑US (0.2002 l/km)) and was thus only awarded 23.9 of the available points. RIT went on to win the overall competition by only 8.9 points over OSU, having scored slightly better in all of the other dynamic events.

Safety

The majority of the regulations pertain to safety. Cars must have two steel roll hoops of designated thickness and alloy, regardless of the composition of the rest of the chassis. There must be an impact attenuator in the nose, and impact testing data on this attenuator must be submitted prior to competing. Cars must also have two hydraulic brake circuits, full five-point racing harnesses, and must meet geometric templates for driver location in the cockpit for all drivers competing. Tilt-tests ensure that no fluids will spill from the car under heavy cornering, and there must be no line-of-sight between the driver and fuel, coolant, or oil lines.

FSAE CAR SIMULATION STRAIGHT TRACK

Geometry File

In this case, the FSAE car is placed in a straight track wind tunnel. The wind tunnel dimensions are shown in the first image.

Mesh

Setup

Fluid - Air
Species - N2 & O2
Solver - Transient
Start Time - 0 s
End Time - 1.9s
Turbulence Model - K - Omega SST

Boundary Conditions

Inlet

Inlet - Inflow
Velocity = 12.5 m/s
Temperarture = 300 K

Outlet

Outlet - Outflow
Pressure = 101325 Pa
Temperarture = 300 K

Car Components

Law of wall
Wall BC

Results

Velocity Contour

Forces Report Nomenclature

Pressure_force_X = Drag Force

Pressure_Force_Z - Downforce Force

Body

Rear Wing

Front Wheels

Rear Wheels

Front Wing

Velocity Plot

Cell Count

FSAE CAR SIMULATION TURNS CASE