Use of shock tunnels for hypersonic propulsion testing

Shock tunnels represent a powerful tool for simulating hypersonic flow conditions as they occur during hypersonic flight and reentry. For propulsion testing it has been demonstrated that they are capable not only to allow the outer and intake flow field of complex propulsion systems but also important phenomena inside of the engines like fuel mixing and supersonic combustion. In the Aachen shock tunnel TH2 experiments have been performed with simple and complex ramp geometries to study typical intake flow phenomena. For this a high Mach number, high Reynolds number flow condition is used. But for hypersonic flight vehicles a simulation in wind tunnels as accurate and realistic as possible requires to simulate the high wall temperatures occuring in flight as close as possible. Therefore, in a first attempt a 24 degree ramp model was heated from the inner side by electrical resistance heating elements. The maximum temperature achieved so far amounts to 690 K. In order to increase the total enthalpy of the flow, a detonation driver has been developed which in near future will replace the conventional helium driver of the shock tunnel TH2. Up to now experiments have been performed with the detonation driver in the shock tube mode with a short 6 m long driven section. Results achieved with this facility (THD) show the feasibility of the detonation driver concept for shock tunnel applications over a wide range of flow conditions. THE AACHEN SHOCK TUNNEL TH2 The shock tube of the Aachen shock tunnel has an inner diameter of 140 mm with a wall thickness of 80 mm. The lengths of the driver and driven section are 6 m and 15.4 m, respectively. The building which *Professor, Member AIAA tResearch Engineer Coypright 01999 by the American Institute of Aeronautics and Astronautics Inc. All rights reserved. houses the shock tunnel was especially built for the use of such tunnels. A 800 mm steel-enforced concrete wall which separates the rooms for driver and driven section serves as a protecting wall but is also used for supporting the recoil absorbing system of the tunnel. Driver and driven section are separated by a double-diaphragm chamber which at maximum pressure utilizes two 10 mm thick stainless steel plates as diaphragms scored in the form of a cross by a milling cutter. Another diaphragm of brass or copper sheet is located between the driven section and the nozzle entrance. The maximum operating (steady) pressure of the complete tube is 1500 bar. The driver can electrically be heated to a maximum T4 of 600 K. There are two conical nozzles available, one with a half opening angle of 5.8 degree with an exit diameter of 586 mm and one with 10.5 degree and an exit diameter of 572 mm. For the last one two other truncated cones allow nozzle exit diameters of 1 m and 2 m. The nozzle throat diameter and therefore, the test section Mach number can also be changed by inserting different throat pieces. A contoured nozzle is available for a nominal exit Mach number of 7. In Fig. 1 a side view to scale is shown of the shock tunnel with the 5.8 degree conical nozzle. During the last years the tunnel has mainly been operated under test conditions which are listed in Table 1. Helium is used as driver gas and synthetic air as test gas. The main purpose of these conditions is to study the influence of real gas effects on hypersonic aerodynamics. Therefore, the stagnation temperature is varied between 1500 K and 4700 K which covers perfect gas behaviour at the lower and real gas behaviour at the upper limit with significant oxygen dissociation behind the bow shock. Of course, not only these test conditions can be generated but also a variety of other test section flows which are within the operating characteristics of the shock tunnel. Especially for studying the intake flow in a hypersonic propulsion engine, test condition X with an unit Reynolds number of 16.5 million per meter was calibrated.