Department of Aerospace Engineering
Indian Institute of Science, Bengaluru
HST1, shown schematically below, consists of a shock tube portion attached to wind tunnel portion which is a hypersonic nozzle - test section - dump tank - high vacuum system assembly. The shock tube portion is a constant area cylindrical duct whose inner diameter is 50 mm for a length of 7 m. The shock tube which is made up of aluminium, is divided into 2 m long driver section and 5 m long driven section by placing a metal diaphragm in-between the sections. A thin paper diaphragm separates the shock tube portion from the wind tunnel portion. The HST1 generally operates at Mach 6 in the straight through mode by using a conical nozzle whose entry diameter is 50 mm and exit diameter is 300 mm. However the flow Mach number could be varied by attaching a throat portion between the shock tube and the nozzle. The test section whose length is 450 mm and cross section is 300 mm x 300 mm, is attached to a 1.5 m long cylindrical dump tank whose diameter is 1m.
HST2 is built to overcome the limitations on performance capabilities of HST1. Since the shock tube in the HST1 is made of aluminium, the range of operating pressure levels are limited and hence the tunnel could not produce high enthalpy flows suitable for testing at flow velocities beyond 1.5 km/s. In addition, the test-section-dump tank assembly in the HST1 is made of cast iron which contaminates the hypersonic flow due to the rusting. In order to overcome the above limitations, the shock tube, nozzle, test section and dump tank in HST2 is made of stainless steel material. HST2 can operate in the Mach number range of 6-14 with the help of appropriate nozzle throat inserts and can produce specific flow enthalpies up to 5 MJ/kg. The photographs of HST2 shock tunnel along with the throat inserts are shown below.
HST3 is a free-piston driven hypersonic shock tunnel built to operate at very high enthalpy flow conditions which is limited in the conventional hypersonic shock tunnels because of the limitation on the driver gas pressure required for producing shock waves of higher strength. One way to produce high enthalpy flow conditions is by heating the driver gas temperature which helps to increase the strength of the shock waves in the shock tube, and this is achieved in HST3. HST3 consists of compression tube whose length is 10 m and inner diameter is 165 mm, and shock tube whose length is 4.5 m and inner diameter is 50 mm attached to a convergent-divergent conical nozzle whose exit diameter is 300 mm opens into the dump tank containing the test section. The compression tube is separated from shock tube by a metal diaphragm, and the shock tube is separated from nozzle by a paper diaphragm. The compression tube is filled with helium gas at 1 atm and the high pressure air in the reservoir which is attached to the other end of the compression tube drives a 20 kg piston to a speed of about 150 m/s in the compression tube. This process adiabatically compresses the helium gas to about 10 MPa and heated to about 4500 K. This gas ruptures the diaphragm producing a strong shock wave of Mach numbers exceeding 10 into the driven section. The stagnated test gas behind the reflected shock expands through the nozzle to produce hypersonic flow of Mach 8 with enthalpy exceeding 5 MJ/kg. Different codes such as ESTC, STN, L1D and MBCNS are used to evaluate the tunnel performance.
HST4 is built to accommodate large size test models of about 100 mm in diameter and up to a meter in length, which is unlikely in HST1, HST2 and HST3 shock tunnels. It consists of a shock tube with an inner diameter of 165 mm and a length of 17 m, attached to hypersonic conical nozzle whose half-angle is 10O, entry diameter is 165 mm and exit diameter is 1000 mm, opens into the dump tank containing the test section. The dump tank/test section assembly is 2.85 m long cylindrical tank of 1.50 m diameter. BK 7 optical glass view ports with a window diameter of 367 mm are mounted on the test section to facilitate flow visualization. Test times up to 4ms can be obtained in this facility.
HST5 is a combustion driven hypersonic shock tunnel built to operate at high enthalpy conditions using minimum amount of driver gas. It consists of shock tube of inner diameter 105 mm with driver and driven lengths of 3.5m and 9m respectively and attached to a hypersonic nozzle-test section-sump tank-high vacuum system assembly. A mixture of hydrogen, helium and oxygen gas is combusted in the driver section of shock tube using four spark plugs mounted circumferentially at right angles close to the diaphragm station in the driver tube. The pressure and temperature increases due to combustion and ruptures the diaphragm creating a shock wave in the driven tube, producing a reservoir of high pressure and temperature test gas behind the reflected shock wave which is further expanded through convergent-divergent conical nozzle to produce a hypersonic Mach flow. The free-stream conditions of HST5 depend on driver gas pressure, driver gas temperature, specific heat ratio of driver gas and driven gas pressure unlike free-stream conditions of conventional shock tunnel which depend only on driver gas pressure and driven gas pressure.