Case (a)Normal
Normal case is used to compare to other study cases which is the commercial pickup accessories.
From the results, the pressure pathline of airflow can be investigated to discuss for drag coefficient.
In Fig. 7 (a) is observed that, when the air pressure flow impact to the front area, causes separation and recirculation air on pickup box,
it's called "wake", which in this case have large size because high different of pressure between front to rear of pickup,
which can be discussed from Equation (2).
When the wake impacts to the inside of the box causing the total drag force of pickup is high.
Therefore, the generally normal case has high drag coefficient value.