Computational Assessment of a 3-stage Axial Compressor Which Provides Airflow to the Nasa 11- by 11-foot Transonic Wind Tunnel, including Design Changes for Increased Performance

New rotor blades are to be fabricated for the 24 foot diameter, 3-stage axial compressor which provides airflow in the 11by 11-Foot Transonic Wind Tunnel Facility at NASA Ames Research Center in Moffett Field, California. This presents an opportunity to increase the peak Mach number capability of the tunnel by redesigning the compressor for increased pressure ratio. Simulations of the existing compressor from the APNASA CFD code were compared to performance predictions from the HT0300 turbomachinery design code and to compressor performance data taken during a 1997 facility checkout test. It was found that the existing compressor is operating beyond the stability limits predicted by the analysis tools. Additionally, CFD simulations were sensitive to endwall leakages associated with stator button gaps and under-stator-platform flow recirculation. When stator button leakage and cavity recirculation were modeled, pressure rise at design point increased by over 25% due to a large reduction in aerodynamic blockage at the hub. After improving the CFD model and validating the tools against test data, a new design is proposed which achieved 10.5% increased total pressure rise and substantially reduced diffusion factors. INTRODUCTION A large 24 foot diameter 3-stage axial compressor powered by variable-speed induction motors provides the airflow in the closed-return 11by 11-Foot Transonic Wind Tunnel (11-Foot TWT) Facility at NASA Ames Research Center at Moffett Field, California. The facility is part of the Unitary Plan Wind Tunnel which was completed in 1955. The tunnel has been used extensively for development of fixed-wing airframes since the 1960s. The test section is currently capable of Mach number ranging from 0.20 to 1.45 and Reynolds number ranging from 300,000 to 9,600,000 [1]. Over its history, upgrades to the 11Foot TWT such as flow conditioning devices and additional instrumentation have increased blockage and pressure loss, reducing the peak Mach number capability of the test section. A desire exists to increase the peak Mach number to 1.5 or greater. The compressor operating line and the associated test section Mach number are shown in Figure 1. Figure 1: Compressor and facility operating lines. 1 1.1 1.2 1.3 1.4 1.5 150