Question $8$:

Consider the open circuit type low$-$speed wind tunnel as shown in the figure. The ambient air is used to provide a low speed uniform flow in settling chamber. The contraction ratio for the nozzle is $\frac{A_1}{A_2}=8.$ The pressure difference between the walls of the settling chamber $(P_1)$ and the test section $(P_2)$ is given as $150$ mm water column. Calculate the net normal force per unit area exerting on the test section walls as a result of the interior and exterior pressure difference $(P_2-P_{\text{a}\text{t}\text{m}}).($Hint: The air outside the tunnel is assumed to be stagnant.$)$