Numerical Investigation of Diffusers in Arc-Heated Wind Tunnel: Introducing a Novel and Efficient Hypersonic Diffuser

Abstract

To develop an efficient hypersonic diffuser, a numerical investigation was performed on a center-body diffuser and a second-throat cylindrical diffuser of a large-scale arc-heated wind tunnel with a Mach number 6 nozzle. The length of the diffuser was set to 16 m, and the total pressure and temperature were over 28 atm (2,837 kPa) and 2,000 K to simulate a 13-MW wind tunnel. The ARCFLO4 code was used for the investigation and flow analysis, with air as the working gas inside the wind tunnel, assumed to be in thermal and chemical equilibrium. The axisymmetric Reynolds-averaged Navier-Stokes equation was used as the governing equation. The flow structure and characteristics inside each diffuser were analyzed and compared, and a novel diffuser shape locating a center body in the subsonic region was proposed to compensate for the disadvantages of each diffuser. Moreover, the performance of each diffuser was evaluated based on the maximum efficiency, cooling effect, and exit velocity. The proposed diffuser showed the lowest exit temperature, enthalpy, and velocity with high efficiency; therefore, the proposed diffuser is expected to reduce the cost of wind tunnel installation and operation, alleviating the requirements of the heat exchanger or vacuum chamber. By performing a numerical investigation on general diffuser types of a high-enthalpy wind tunnel, a novel diffuser is introduced here that can lower the exit velocity, temperature, and enthalpy of the internal flow. The proposed diffuser has a center body with a cooling system in the subsonic flow region to minimize the total pressure loss and reduce flow velocity and temperature. In particular, it is effective in reducing the elevated flow temperature due to the shock wave of the supersonic flow. This study is applicable to not only the diffuser but also pipe flow; kinetic energy loss may occur due to the center body by reducing effective area, but the efficiency of the device is almost maintained, but the temperature and enthalpy of the flow are reduced. By adding a center body, it is possible to design and manufacture an efficient new device; further, it may have the advantages of extending the operating range to an existing device by adding a center body.