Shojiro Kaji

Department of Aerospace Engineering Teikyo University

1-1 Toyosato-dai, Utsunomiya 320-8551 Japan

kaji@koala. mse. teikyo-u. ac. jp

Takahiro Suzuki

Department ofAeronautics and Astronautics University of Tokyo

7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 Japan

Toshinori Watanabe

Department ofAeronautics and Astronautics University of Tokyo

7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 Japan

watanabe@aero. t.u-tokyo. ac. jp

Abstract Interaction between a sonic boom and cascaded blades is studied numerically.

The incident sonic boom is modeled by a finite amplitude N wave with a short rising time, and the time dependent transonic cascade fbw with a passage shock inside is solved. Detailed mechanism on refection and transmission of a sonic boom by the cascade and unsteady aerodynamic force exerted on blades are elucidated. The peak amplitude of the unsteady blade force is the same order of magnitude as the pressure amplitude of the incident sonic boom.

Keywords: sonic boom, cascaded blades, interaction, supersonic transport,

numerical analysis


K. C. Hall et al. (eds.),

Unsteady Aerodynamics, Aeroacoustics and Aeroelasticity of Turbomachines, 483-491. © 2006 Springer. Printed in the Netherlands.

1. Introduction

In this century, a new era of supersonic transport (SST) is in prospect where a great number of SST is introduced concurrently with subsonic transport. Then, there will be an increasing possibility for subsonic transport of encoun­tering a sonic boom of supersonic transport. In such an occasion shock waves due to a sonic boom of SST are swallowed in an engine inlet and interact with fan rotor blades and stator vanes. In another occasion a sonic boom may invade into the engine cowl from the rear side.

Another example of interaction of shock waves and cascaded blades can be found in an innovative concept of a pulse detonation engine (PDE) combustor combined with a turbine engine. In this case shock waves due to a detonation combustor hit upon turbine nozzle vanes and blades. The strength of shock waves for a PDE combustor reaches more than 200 dB in pressure amplitude. Again we have a strong motivation to investigate the interaction between shock waves and cascaded blades.

The purpose of the present paper is to investigate numerically the impact of a sonic boom produced by SST on the engine fan rotor of subsonic transport. The same problem was treated in the last symposium analytically by use of the semi-actuator disk model for cascaded blades [1]. The results obtained in the analysis showed that (1) the amplitude of the transmitted N wave across the cascade passage shock increases over the incident N wave, (2) the pressure fhctuation at the cascade passage shock has a discontinuous character, and (3) unsteady aerodynamic force exerted on blades by a sonic boom becomes strong in the direction of chord. The numerical approach taken in this paper enables to check the validity of the semi-actuator disk model and give more detailed interaction mechanism.

Similar analyses have been made from different view points. Paynter et al. [2] needed the rear end boundary condition for numerical analysis of an en­gine air intake. They solved the fbw field including the cascade to determine the refection coefficient of sound waves. Freund et al. [3] investigated exper­imentally the refected pressure fhcthation for the disturbance incident upon an engine compressor. Dorney [4] analyzed numerically the effect of sound waves incident upon a viscous transonic cascade.