Princeton University

In an effort to create a new type of hypersonic wind tunnel, high power directed energy sources such as electron beams and lasers are being used to add energy in a controlled way to supersonic air. For a full scale facility the use of multi-megawatt energy sources is envisioned. The radiatively driven hypersonic wind tunnel is being developed to overcome the short run time and poor flow quality of current hypersonic test facilities above Mach 8. This program is carried out in collaboration with a number of US national labs, MSE Inc. and the US Air Force. As an integral part of this program computational fluid dynamic codes that include the energy addition process are being developed to model the radiatively driven process. To date successful proof of principle experiments have been performed by adding energy at the 10 kW level to a supersonic flow using a CO2 laser and an electron beam. A range of laser based diagnostics have been used to quantify flow properties during energy addition. Future work will increase power levels and identify and investigate engineering challenges that must be overcome before large scale facilities can be built.

Shadow Graph Movies of the First Demonstration of Radiative Energy Addition to Supersonic Flow

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• Shadowgraph movie of e-beam heated flow made from 32 images taken 50 miocroseconds apart with an exposure of 5 microseconds. The electron beam irradiates flow for 750 microseconds and measurements of change in total enthalpy show that approximately 10 KW of e-beam power is deposited into the flow. Approximately 50 KW enters the nozzle and most of the power is lost on the nozzle walls. Flow is from the bottom to top of page and the Mach angle of the shock wave created by a small cone is observed to increase with the increase in Mach number. The Mach number decreases from 3.9 to 3.2. (Quicktime movie 1)

• Shadowgraph movie of e-beam heated flow made from 32 images taken 35 miocroseconds apart with an exposure of 3.5 microseconds. The electron beam irradiates flow for 750 microseconds and approximately 90 kW enters the nozzle. Flow is from the bottom to top of page and the Mach angle of the shock wave created by a small cone is observed to increase with the increase in Mach number. The Mach number decreases from 3.9 to 2.4. The non-uniform change in Mach angle across the flow is due to the finite size of the e-beam that is not centered in the nozzle. (Quicktime movie 2)

• Change in Mach number indicated by variation of shock angle seen around total temperature and pressure probe. (Quicktime movie 3)

• Shock structure near the ZnSe window that was used to couple the laser radiation into the nozzle. (Quicktime movie 4)