Investigation of Variable Mach Number Wind Tunnel with Symmetric Sliding Block Nozzles

The Continuously Varying Mach Number Tunnel (CVMT) was commissioned at National Centre for Combustion Research and Development (NCCRD), Indian Institute of Technology Madras. The CVMT is capable of generating variable Mach number flow continuously. This ground test facility is of intermittent, blow-down, enclosed free-jet type. The nozzle profile was designed using the Method of Characteristics (MOC) simulations. The nozzle blocks are translated towards and away from each other symmetrically. The continuous movement of nozzle blocks results in the varying Mach number. The CVMT is characterized using two methods. In the first method, the flow is calibrated using a Pitot rake. In this case, the CVMT is calibrated for different Mach numbers without dynamic movement of the nozzle. In the second method, the CVMT is calibrated with a simple wedge for different Mach numbers with dynamic movement of the nozzle. The resulting Mach numbers with both the methods agree well with each other. In this paper, the design method, nozzle translation mechanism and characterization of the Variable Mach number tunnel with symmetric sliding block nozzle are presented.