Investigation of grid fins on large-scale model test in supersonic wind tunnel

Aerodynamic characteristic and static stability of experimental model with grid fins cannot be simulated veritably in supersonic wind tunnel, as that structural strength of the model cannot meet the requirement of supersonic wind tunnel test, and it is difficult to manufacture the model with small grating thickness and small grid spacing. To cope with these problems, this paper offers an equivalent analog method based on supersonic linearized theory. The equivalent analog method is to design an equivalent model with the same aerodynamic characteristic as that of the grid fin model. The specific implementation of the equivalent analog method consists of the following procedures: overall dimensions and geometric angles between four sides of grid fins remain unvaried, while the grid spacing expands by k times and the amount of the grid reduces by k times; the grid width ratio maintains its value whereas the chord length enlarges by k times; relative thickness keeps unchanged though the thickness of ribs increases by k times; and longitudinal pressure centers of the equivalent and original models are the same. The wind tunnel test of an original model was compared with that of the equivalent model. The lifts in the two tests were identical, and the drags were similar. An identical behavior was observed in the two tests for the aerodynamic characteristics and the static stability. The influence of the drag was insignificant on the centroid and the static stability. The equivalent analog method can present relatively veritable simulation of aerodynamic characteristics and static stability for grid fins, and solve the problems in manufacturing and structural strength of large-scaled model.