Answer:
The suggested default wind tunnel dimensions of the intake size are set to twice the width and height dimensions of the model. Its length is set as three times the model length with a shorter distance at the intake side.
The procedure used to calculate the default wind tunnel dimensions involves a complex testing process that has been optimized. The default dimensions are determined as to provide sufficiently large free space around the structure in the model, and also set as small as possible to obtain short calculation times.
Although the automatic default dimensions should be sufficient, manual changes can be made by the user.
