Wind force on a Nissen hut

A 45 km/h wind flows over a Nissen hut which has a 3.5 m radius and is 54.9 m long (Fig. E4.1). The upstream pressure and temperature are 1.013 E+5 Pa and 288.2K respectively, and they are equal to the pressure and temperature inside the Nissen hut.

(a) Calculate the lift and drag forces on the building.

(b) Find the location θ on the building roof where the pressure is 1.013 E+5 Pa. Assume an irrotational flow motion of ideal fluid in parts (a) and (b).

(c) Calculate the drag force for a real fluid flow.

Notes: The Nissen hut is a building made from a semi-circle of corrugated steel. A variant was the Quonset hut used extensively during World War 2 by the Commonwealth and US military for army camps and air bases. The design was named after Major Peter Norman Nissen, 29th Company Royal Engineers who experimented with hut design and constructed three prototype semi-circular huts in April 1916. The building was not only economical but also portable.