Light gas guns by way of different modes of operation offer both distinct advantages and disadvantages over other hypersonic test facilities such as shock tunnels. These include visualization of flow over models, not influenced by support structure required for shock tunnel testing. This work investigates the capacity of the current T4 shock tunnel facility operating as a helium driving two stage light gas gun. Principal aims include identifying operational limits to achieving hypersonic velocities, i.e. Mach 5 and greater and comparing ideal constant pressure performance with realistic behaviour of the facility.
This is achieved through the use of a quasi-one dimensional solver, l1d3. The simulations required the use of a number of assumptions to describe projectile geometry including mass and relative effects of friction. Values for the relative strength of friction are taken for a conservative estimate proportional to current piston performance in addition to more optimistic values whereby friction is essentially negligible. An iterative method is used to refine initial conditions from the results to identify the maximum safe operating limits for a range of projectile masses and friction values.
It is found that the facility does not behave similar to the ideal constant driving pressure condition, instead experiencing significant overpressure, to detriment of performance. To reach speeds of Mach 5, a variation of maximum projectile mass is found to be between 800g and 1300g depending upon the assumptions made regarding friction, highlighting the need for comprehensive data for friction effects at high sliding velocities. The use of hydrogen as the driving gas launching into an atmospheric pressure are simulated and found to only have small influences at these higher projectile masses. Higher projectile masses can achieve optimal performance at restrain pressures in the vicinity of 10MPa while decreasing projectile mass necessitates an increase in restrain pressure for efficient system operation. Variations in projectile mass are investigated to a limited extent with a proposed framework for future inquiry if sufficient interest exists.