. In transonic wind tunnel testing, the small area decrease caused by placing the model in the test section, i. e., by the model blockage, can cause relatively large changes in the flow in the test section. To illustrate this effect, consider a tunnel that has an empty test section Mach number of 1.08. The test section has an area of 1 m2 and the stagnation temperature of the air flowing through the test section is 25°C. If a model with a cross-sectional area of 0.005 m2 is placed