Journal of Mechanical Science and Technology 29 (11) (2015) 4943~4950 www.springerlink.com/content/1738-494x(Print)/1976-3824(Online) DOI 10.1007/s12206-015-1042-9 Thermal and inertial parameters of the flow field of a scramjet engine † Jigar Sura, Satheesh Kumar and Viren Menezes * Department of Aerospace Engineering, Indian Institute of Technology Bombay, Mumbai, India (Manuscript Received August 15, 2014; Revised July 3, 2015; Accepted July 21, 2015) ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Abstract Heat flux and pressure were measured on the internal walls of a scramjet engine at a hypersonic Mach number of 8 in a shock tunnel. Temperature-time history was recorded on model walls using fast-response thermocouples and the wall heat flux was deduced thereon from the temperature records. Pressure was measured at the same locations as that of heat flux using high-frequency pressure transducers. The surface measurements were used to analyze the internal flow field of the engine. The heat flux measurements revealed the regions of peak heating that may require additional thermal protection during the operation; the regions being the beginning of the constant area duct and the nozzle. The pressure measurements and the pertinent analysis indicated an optimum compression at intake through shock waves with a viable flow separation in the combustion chamber. The experimental data indicated an optimum design of the engine for a possible fuelled operation in future. Keywords: Heat flux; Hypersonic; Pressure; Scramjet ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 1. Introduction Viscous interactions and boundary layer sensitive phenom- ena are the prime characteristics of hypersonic slender bodies. Hypersonic cruise/transport requires deployment of air- breathing slender vehicles for efficient operations, where the scramjet- integrated slender geometries are believed to be apt. Efficiency of a scramjet engine depends on the modulation of its internal flow field, which involves a trade-off between flow compression through ramps at the inlet and flow separation in the isolator/combustion chamber due to the impinging shock train [1, 2]. The compression through the ramps at intake should be sufficient to slow down the flow in the combustor and produce a conducive ambience for fuel injection and igni- tion, while the shock train in the isolator/combustor should exert a pressure gradient that can be surmounted by the boundary layer without a major flow separation. Heat transfer from the flow to the wall is a boundary layer sensitive parameter and is a critical information required in the design of thermal protection systems for hypersonic vehicles [3]. The high kinetic energy of the hypersonic flow is trans- formed into the internal energy due to viscous dissipation in the boundary layer and the rise in temperature close to the wall sets in heat conduction from the last layer of the fluid to the wall. As the wall heat transfer is directly proportional to the kinetic energy of the flow, the temperatures on the walls of hypersonic vehicles could be enormous. In addition to this, the shock train impinging on the walls of the combustion chamber in a scramjet engine gives rise to local peaks of heat transfer, which can be detrimental unless accurately estimated and subverted through the use of an appropriate thermal protection system or a heat resistant material. Hence, the measurement and analysis of wall heat transfer in a hypersonic shock wave- boundary layer interactive ambience plays a vital role in envi- sioning the aerothermodynamics of the vehicle [4]. The com- pression in a scramjet engine is achieved through shock waves at the intake and then through a shock train in the isola- tor/combustor. The shock waves and the train impose an ad- verse pressure gradient that may cause the flow to separate and cause distortion in the combustion chamber [5]. Hence, the pressure distribution in the engine reveals its inertial flow field, the knowledge of which is essential for suitable modula- tion and efficient operation of the engine. With an objective of investigating the thermal and inertial parameters of the flow field of a scramjet engine, we carried out heat transfer rate and pressure measurements on the inter- nal surfaces of a double-ramped, symmetric scramjet engine. The measurements were carried out in a hypersonic shock tunnel, in a freestream of Mach 8 (±2.5%), without fuel injec- tion. The objective of the investigation was to understand the aerothermodynamics of the engine and to ensure an internal flow field suitable for an efficient operation. The measure- ments were carried out by distributing E-type, coaxial thermo- couples and high-frequency pressure transducers in the walls of the test model. The heat flux and pressure distributions on * Corresponding author. Tel.: +91 22 25767130, Fax.: +91 22 25722602 E-mail address: viren@aero.iitb.ac.in † Recommended by Associate Editor Jeong Park © KSME & Springer 2015