Facilities

High Temperature Supersonic Jet

The High Temperature Supersonic Jet Facility, commonly referred to as the Hot Jet Facility, is a state-of-the-art facility that is used to simulate the exhaust produced by jet engines. Through the use of a sudden expansion (SUE) burner, the facility is capable of generating the high-temperature, high-pressure airflows that are needed for an accurate simulation. The facility can accommodate nozzles having exit diameters up to 76.2 mm (3 in.) and a design Mach number of up to 2.5. The jet from the nozzle exhausts into a fully anechoic chamber that measures 5.8 m x 5.2 m x 4.0 m. After traveling 3.4 m, the jet is exhausted to the atmosphere by way of an acoustically treated duct. During experiments, the temperature and the pressure of the airflow are controlled through the use of LabVIEW-based programs. For smaller nozzle sizes, the desired nozzle pressure ratio (NPR) and stagnation temperature can be held to within 1.5% of the desired value. For larger nozzles, the NPR and stagnation temperature can be held to within 0.5% of the desired value.

The primary use for the facility is the study of high-speed jet noise and techniques for reducing said noise. As such, up to 12 B&K model 4939 microphones can be setup in the anechoic chamber. The microphones are setup in a polar arc that is centered on the nozzle exit. An aluminum rail is used to establish this arc and it permits placement of the microphones in one-degree increments from 80 to 155 degrees, with respect to the upstream jet axis. The signals from the microphones are band-pass filtered from 20 Hz to 100 kHz and then simultaneously sampled through the use of a MATLAB-based program. During experiments, the conditions in the anechoic chamber, such as room temperature and relative humidity, are logged and then these conditions are taken into account when processing the acoustic data that was acquired.

The technique of microjet injection is currently being used for high-speed jet noise reduction in the facility. This technique is used because it has a high momentum flux with a low mass flow rate. The microjets are generated through the use of micro-nozzles that are located around the nozzle exit. The operating medium of the microjets is usually either nitrogen or water and the NPR is varied from 7.8 to 48.6. Recent tests have shown that high-pressure water injection is capable of mitigating the noise sources that are present at supersonic speeds. This results in a reduction of up to 7 dB at the peak radiation direction through the use of this technique.

The Office of Naval Research funded the construction of the facility, and they continue to provide the necessary funds for operating the facility. Dr. Krothapalli oversees the research that is conducted in the facility and two Ph.D. students, Brent Greska and Sandeep Yerapotina, currently conduct the experiments in the facility. For further information regarding the facility, please contact either Dr. Krothapalli at (850) 644-5885 or Brent Greska at (850) 644-1458.