Erinc Erdem

Penetration Characteristics of Air, Carbon Dioxide and Helium Transverse Sonic Jets in Mach 5 Cross Flow

An experimental investigation of sonic air, CO2 and Helium transverse jets in Mach 5 cross flow was carried out over a flat plate. The jet to freestream momentum flux ratio, J, was kept the same for all gases. The unsteady flow topology was examined using high speed schlieren visualisation and PIV. Schlieren visualisation provided information regarding oscillating jet shear layer structures and bow shock, Mach disc and barrel shocks. Two-component PIV measurements at the centreline, provided information regarding jet penetration trajectories. Barrel shocks and Mach disc forming the jet boundary were visualised/quantified also jet penetration boundaries were determined. Even though J is kept the same for all gases, the penetration patterns were found to be remarkably different both at the nearfield and the farfield. Air and CO2 jet resulted similar nearfield and farfield penetration pattern whereas Helium jet spread minimal in the nearfield.

Experimental Studies on Micro-Ramps at Mach 5

The performance of hypersonic propulsion can be critically affected by shock wave/boundary layer interactions (SBLIs), whose severe adverse pressure gradients can cause boundary layer separation. This phenomenon is very undesirable in engine intakes leading to total pressure loss and flow distortion which can cause engine unstart. Hence, it is essential to apply flow control method to the flow, either at the beginning or during the interaction phenomenon to prevent the shock-induced separation [1].

Incident Shock-Transverse Jet Interactions at Mach 1.9: Effect of Shock Impingement Location

The scramjet engine is an efficient design for high-speed propulsion, requiring injection of fuel into a supersonic flow in a short amount of time. Due to the nature of the flow numerous shock waves exist within the combustor of a scramjet, significantly altering the flow characteristics and performance of the engine as the flow Mach number or attitude is changed. According to Mai et al. [1] the location of impingement of the incident shock, relative to the fuel injection location, has significant impact on the mixing and flame-holding properties. This emphasises the importance of understanding and hence the need for controlling the dynamic interactions that are created. Of course another fertile area where transverse jet injections are studied for their application is the creation of forces and moments for pitch and attitude control [2, 3].

Single Pulse Laser Energy Deposition in Quiescent Air and Hypersonic Flows

Single laser energy deposition was experimentally investigated in both quiescent air and hypersonic flow. The induced flow pattern and the resulted perturbation to the hypersonic flow are observed using high-speed schlieren photograpay. A laser induced plasma was obtained by focusing a Q-switched single pulse Nd:YAG laser (wavelength 532 nm) with maximum laser energy of 203 mJ per pulse using a combination of concave-convex lenses. Initially, single pulse laser energy deposition was conducted in quiescent air at 101 kPa. Then, the laser beam was focused upstream of a truncated cone model as well as in the boundary layer above a flat plate in Mach 5 flow. In the quiescent air, the speed of the induced shock wave decays rapidly with time and the strength of the shock wave is weakened as it propagates outward. In the presence of hypersonic flow, the induced shock wave propagates downstream and interacts with the bow shock wave in front of the truncated cone. The bow shock wave is significantly mitigated with an effecting time of 450 μs after the laser pulse. Over the flat plate, the induced shock wave perturbs the boundary layer and causes separation in the adjacent upstream. A separation shock wave is formed due to the existence of a separation region. The entire structures are similar to that flow pattern induced by pulse micro-jet. The propagation of the induced shock wave changes the local pressure distribution and a stronger pressure disturbance is found in the downstream compared to than the upstream of the focal point.

Application of Pressure- and Temperature-Sensitive Paint in a Hypersonic Double Ramp Flow

Pressure- and Temperature-Sensitive Paint (PSP, TSP) was considered as novel nonintrusive flow diagnostics which can provide quantitative global surface pressure and temperature mapping on complex geometry with high spatial resolution [1]. PSP and TSP has been mainly applied in transonic flows [2, 3, 4], supersonic flows [5, 6, 7] and low speed flows [8]. The application of PSP and TSP has been extended to hypersonic flow [9, 10, 11] but not reported as many as at the other flow conditions. The testing condition is challenging for PSP measurement in hypersonic mainly based on the following reasons. The critical aerodynamic heating will cause considerable error for the PSP measurement because of thermal quenching mechanism.

Effect of Roughness in Jets in Mach 5 Cross Flow

Transverse jet injection into supersonic/hypersonic cross flow has been encountered in many engineering applications ranging from scramjet combustors and solid rocket motor or liquid engine thrust vector control systems to high speed flying vehicle reaction control jets. These applications all involve complex three dimensional flow patterns comprising separated regions, shock waves, shear layers and wakes in common. Owing to numerous applications and these complicated flow features, transverse injections over different geometries and various forebodies have been received significant amount of interest. Earlier studies were focused on wind tunnel experiments and the utilisation of conventional measurement techniques such as Schlieren/Shadowgraph photography, wall pressure and concentration measurements to better understand the jet interaction and penetration phenomena. These studies aimed to assess the effect of injection pressure ratio, location of injection and state of incoming boundary layer and type of injectant gas on jets in supersonic/hypersonic cross flow. Recent studies of missile/forebody applications involving reaction control jets by several researchers have investigated jet interaction phenomenon on various axisymmetric body configurations at supersonic/ hypersonic speeds [1, 2, 3, 4]. Their aim was to investigate control effectiveness of transverse/lateral jets on different missile body configurations.

Interaction between Laser Induced Plasma and Boundary Layer over a Flat Plate in Hypersonic Flow

Laser energy deposition has brought great interest to researchers due to its applications in drag reduction [1, 2], shock wave modification [3, 4], fuel ignition [5], and optical perturber for transition study [6, 7, 8]. Compared to the electric discharge flow control techniques, laser energy deposition can excite the flow non-intrusively with almost any pulse-width and repetition rate [9] with out any electrodes.