Theoretically, the shape of a vehicle in motion causes the airflow to create force that acts on the surface of the vehicle. The drag coefficient (Cd) depends mainly on the shape of the vehicle, regardless of its size or driving speed. Several designs used in the CFD analysis and the result shows the pressure distribution, separation points as well as the wake generated at the rear of the vehicle.
The drag coefficient depends mainly on the shape of the vehicle, regardless of their size or speed. The drag coefficient thus gives a good indication of the relative merits of different vehicle shapes. The author will focus more on the first part of the project, which is aerodynamic body design and analysis.
The movement of the airflow near the body creates a velocity distribution which in turn creates the aerodynamic loads acting on the vehicle. If the pressure varies in the flow direction, the behavior of the boundary layer flow can be strongly influenced. Because the liquid can no longer follow the contours of the surface, it breaks off.
In the study of ground vehicles, the behavior of the boundary layer is responsible for the shape of the vortex development and the regions of separated flow on the vehicle.
P - Pato = Zpv2atm " hP?
Cp=\~[v2/v2atm]
VnP= V2pV2atm KCpf-Cpr)dA
D„p= I/2pv2ctlm(Cpf-CPr)
As previously mentioned, the team's responsibility lies solely with the vehicle bodywork. Therefore, the concept sketches are created based on observation, experience and interpretation, and so is much of the decision-making about the concept and style of the car. The drawing process can be repeated on a certain part of the vehicle, based on the aerodynamic requirements, until a good design selection is achieved.
Some significant modifications may need to be made to certain parts of the vehicle, as explained in the literature review section, until the vehicle had low Cd and Cl values. The main options currently available in STAR-CD for general applications are variants of the well-known k-e model, all of which include transport equations for turbulent kinetic energy k and its dissipation rate e. Experimental measurements of the pressure distribution on the car body were also provided of the analysis.
There is a certain amount of space in the front, side and rear of the car. The large amount of stagnation (pressure) at the front of the model was due to large. The figure above shows the speed profile of the early design before an adjustment is made based on the result obtained in this analysis.
There are several forms of counter rotating tops at different speeds and this has affected the air flow pattern at the rear of the vehicle. The flat corner and sharp edge tend to create severe separations in the front of the vehicle. Additionally, the low front stall line has the advantage of reducing hft at the front.
The role of aerodynamicists is to achieve low drag for the chosen configuration. An important factor in the letter-shaped rear is the p, which is formed by the line connecting the rear of the roofline with the tip of the trunk (trunk). Raising the underside increases the taper back and thus reduces the drag shape.
Both graphs (Design 1 and 2) show the model of the pressure coefficient (Cp) acting on the vehicle body. Cp is calculated from 20-30 pressure points taken along the body of the vehicle, starting immediately after the stagnation point and ending at the rear of the vehicle.
V2pA7 utm
Returning to the pressure distribution figure, the P value at this section is still higher than the atmospheric (ambient) pressure. As the air travels over this part, the airflow is still attached.
Cn=l!A ICpdA
Referring to the figure above, we can see the flow profile acting on the surface of the vehicle. The air flows along the upper surface of the vehicle and under the vehicle as well. The flow pattern shows that it is more likely the streamlined half-body at a ground plane.
After reattachment, the currents appear to be able to follow the shape of the vehicle body until it reaches the upper (roof) portion. Going back to the original model, separation occurred at the bottom of the windshield. Although the flow in the experiment was almost along the upper body surface, the flow began to separate from the body surface at the roof end.
A large wake was formed due to flow separation at the rear of the vehicle. This may be the main contribution to the low drag force exerted on the rear of this model. Other aspects that produce drag in the flow around the vehicle are the conical vortices which are created by the separations from the A-post in the font and at the rear.
Computational fluid dynamics (CFD) will play an important role in the design analysis at this stage of the project. The Computational Fluid Dynamics (CFD) analysis was done continuously throughout the second semester of the final year project until the final design of the vehicle was obtained. Furthermore, there are many problems related to the 3-D drawing of the model and this has affected the simulation analysis.
That is why all the computational fluid dynamics or the simulation analysis was performed in 2D approaches. However, the method used in determining the drag force and drag coefficient applied to the vehicle model is applicable and the results obtained are not much different from the 3D analysis. The availability of the equipment itself and the cost limitation for this project may be the main reasons.
Therefore, based on the analysis and the result obtained, computational fluid dynamics can still be relied on to perform the external aerodynamic analysis of the vehicle body. 12] Aerodynamic simulation of vehicles, 2003
