As one of the wave drag reduction methods in supersonic regime,
Busemann's Biplane is well known.
It reduces the wave drag by the interference of the shock and expansion waves which generate between the biplane.
It is known that the wave drag was minimized at the position that shock wave,
which generating from the leading edge of one half-wedge wing, hits the peak of the other half-wedge wing. (Fig.1)
For the confirmation of this phenomenon, following 2 cases were analyzed by Euler flow simulation using an unstructured mesh method. Case1 was exactly Busemann's Biplane as shown in Fig.2. At Case2, lower wing geometry and the position between the two wings (‡™Z) were same with that of Case1. The upper wing was modified from the half-wedge wing to almost a flat wing as shown in Fig.3.
Flow analysis was conducted in the flow condition that the Mach number of 2.5. In Fig.4, the pressure contours are shown. At the Case1, it was confirmed that the generated shock waves were almost disappeared by the interference between the two wings. So it can reduce the shock waves arriving to the ground, which resulted in the sonic-boom reduction. The pressure drag (which including wave drag) of Case1's biplane was almost quarter of that of Case2 !! Moreover, by the use of the moving mesh method based on spring analogy, it was also confirmed that the minimization of the drag was truly realized at the position that the shock waves hit the peak of the half-wedge wing. (movie here) Therefore, the advantage of the Busemann's Biplane is not only the reduction of the wave drag, but also the reduction of the sonic-boom (noise generated by shock waves). The concept of Busemann's Biplane has been investigated vigorously in Japan for the application to 'Boomless Supersonic Transport'.
Do you want to get more link of the supersonic biplane ? * Japanese (PDF) * English (PDF) |
