H. T. Nagamatsu

Brazilian Activities On The Laser‐Supported DEAS In Hypersonic Flow

The present paper presents recent (original) and previous experimental results on the Laser‐Supported Directed Energy “Air Spike” — DEAS in hypersonic flow achieved by the Laboratory of Aerothermodynamics and Hypersonics — LAH, Brazil. A CO2 TEA laser has been used in conjunction with the IEAv 0.3m Hypersonic Shock Tunnel — HST to demonstrate the Laser‐Supported DEAS concept. A single laser pulse generated during the tunnel useful test time was focused through a NaCl lens ahead of an aluminum hemisphere‐cylinder model fitted with a piezoelectric pressure transducer at the stagnation point. In the more recent experiments, the simple hemisphere‐cylinder model was substituted by a Double Apollo Disc model fitted with seven piezoelectric pressure transducers and six platinum thin film heat transfer gauges. The objective being to corroborate the past results as well as to obtain additional pressure distribution information and new heat transfer data.

Bow Shock Wave Mitigation by Laser-Plasma Energy Addition in Hypersonic Flow

Experimental results of bow shock wave mitigation by laser-plasma energy addition in a low-density Mach 7 hypersonic flow conducted in a shock tunnel are presented. A high-power pulsed CO2 laser operating with 7 J of energy and 30 MW of peak power was used to generate the plasma ahead of a hemispherical model installed in the tunnel test section. The schlieren technique was used to visualize the time evolution of energy addition to the flow by laser-induced plasma and the interaction between this disturbed region and the inherent bow shock formed on the model by hypersonic flow. A complete mitigation of the bow shock profile under action of the energy addition was observed. The impact pressure on the hemispherical model measured at the stagnation point reveals the correlation between the schlieren images and the pressure reduction.

Schlieren Visualization Technique Applied to the Study of Laser-Induced Breakdown in Low Density Hypersonic Flow

Experimental results on the visualization of the time evolution of the laser‐plasma induced breakdown produced in low density hypersonic flow using the Schlieren technique are presented. The plasma was generated by focusing the high power laser pulse of a CO2 TEA laser in the test section of the IEAv 0.3m Hypersonic Shock Tunnel. An ultra‐high speed electronic tube camera was used to register the event. The photographs reveal the expansion of the shock wave produced by the laser generated hot plasma and the convection of the plasma kernel by the hypersonic flow. It is also observed the interaction between the plasma disturbed region and the shock established by the flow around an hemisphere‐cylinder model. A strong change in the shock wave structure near the model was observed, corroborating the DEAS concept.

Experimental Analysis of Heat Flux to a Blunt Body in Hypersonic Flow with Upstream Laser Energy Deposition — Preliminary Results

Due to high heat transfer rates in hypersonic flight and its consequent necessity of prohibitively massive thermal protection system, new methods of flow control are required to enable flight in such regimes. Here arises the Direct Energy Air Spike concept, where electromagnetic energy (laser/microwaves) is focalized upstream of the model causing the breakdown of the air and the generation of a Laser Supported Detonation wave which diverts the incoming stream parabolically. In this preliminary work, the heat transfer rates to the surface of a blunt body, downstream the laser induced shock wave, were qualitatively measured and compared with the results without the DEAS. These measurements were conducted with the use of fast response coaxial thermocouples and piezoelectric pressure transducers installed on the surface of the model in the 0.30m IEAv’s T2 Hypersonic Shock Tunnel. The laser energy was supplied by a CO2 TEA Laser.

Numerical Investigation of Vibrational Nonequilibrium Effects in Hydrogen - Oxygen Rocket Engines

A computational method has been developed to simulate gas nozzle e ows expanding in vibrational nonequilibrium. Comparisons of the effect of nonequilibrium on e owe eld variables are made with available experimental data. Several experimental investigations of expanding nitrogen e owe elds are simulated and compared. Signie cant changes in the properties of e owe elds with a large degree of nonequilibrium are predicted. Nonequilibrium velocities in excess of the equilibrium values are predicted for the initial expansion process. Vibrational nonequilibrium in oxidizer-rich core e ows of hydrogen ‐ oxygen rocket engines is then investigated computationally. Vibrational relaxation rate data of oxygen in combustion product gases are obtained from experimental data, empirical correlations, and extensions of available theory. Nonequilibrium e owe eld effects are computed and shown to be minor in terms of performance losses caused by relatively rapid vibrational relaxation of oxygen in the product gas mix. Temperature measurements based upon vibrational population are subject to signie cant error, however. Uncertainty in the relaxation rate of oxygen in water vapor leads to large ranges in computational results.

Multi Laser Pulse Investigation of the DEAS Concept in Hypersonic Flow

The present paper presents recent experimental results on the Laser‐Supported Directed Energy “Air Spike” — DEAS in hypersonic flow achieved by the Laboratory of Aerothermodynamics and Hypersonics — LAH, Brazil. Two CO2 TEA lasers, sharing the same optical cavity, have been used in conjunction with the IEAv 0.3m Hypersonic Shock Tunnel — HST to demonstrate the Laser‐Supported DEAS concept. A single and double laser pulse, generated during the tunnel useful test time, were focused through a NaCl lens upstream of a Double Apollo Disc model fitted with seven piezoelectric pressure transducers and six platinum thin film heat transfer gauges. The objective being to corroborate previous results as well as to obtain additional pressure and heat flux distributions information when two laser pulses are used.

Combustion shock tunnel and interface compression to increase reservoir pressure and enthalpy

This article discusses the production of hypervelocitv -hypersonic flows in a combustion shock tunnel operating in the equilibrium interface mode. In this mode of operation, the additional compression provided by the approaching interface is used to obtain higher pressures and temperatures, as opposed to the reflected method. A computer code was developed to model the operation of a shock tunnel in the equilibrium interface condition. In this article, all the calculations were made for the Rensselaer Polytechnic Institute (RPI) 1.22-m-diam Combustion Driver Hypersonic Shock Tunnel. The major drawback of the interface compression technique, which is the contamination of the driven gas by the driver gas, was overcome through the utilization of a small volume region separating the two gases. Numerical results indicate that the RPI facility will be able to generate reservoir temperatures of the order of 20,000 K and reservoir pressures of the order of 30,000 psi. These reservoir conditions can be used to produce test section Mach numbers of 35.

Development of a New Hypersonic Shock Tunnel Facility to Investigate Electromagnetic Energy Addition for Flow Control and Basic Supersonic Combustion

A new 0.6‐m. diameter Hypersonic Shock Tunnel is been designed, fabricated and will be installed at the Laboratory of Aerothermodynamics and Hypersonics IEAv‐CTA, Brazil. The brand new hypersonic facility, designated as T3, is primarily intended to be used as an important tool in the investigation of supersonic combustion management and of electromagnetic energy addition for flow control. The design of the runnel enables relatively long test times, 2–10 milliseconds, suitable for basic supersonic combustion and energy addition by laser experiments. Free stream Mach numbers ranging from 6 to 25 can be produced and stagnation pressures and temperatures of 200 atm. and 5,500 K, respectively, can be generated. Shadowgraph and schlieren optical techniques will be used for flow visualization and the new facility is expected to be commissioned by the end of 2006.

Flow Visualization of Laser‐Induced Air Spikes in Hypersonic Flow

Flow visualization of laser energy addition upstream blunt bodies in hypersonic flow was achieved by means of open shutter photography and high‐speed cameras techniques. The laser energy was supplied by two CO2 TEA lasers, sharing the same optical cavity, while the hypersonic flow was generated in the IEAv 0.3m Hypersonic Shock Tunnel — HST test section. Single and double laser pulses, generated during the tunnel useful test time, were focused through a NaCl lens upstream a simple hemisphere‐cylinder and Double Apollo Disc models. A regular SLR camera, a high‐speed CCD camera and an ultra‐high speed electronic tube camera provided imaging. Preliminary results using the ultra‐high speed camera in a shadowgraph/schlieren arrangement revealed the dynamic complex flow structure that is established during the addition of the laser energy to the hypersonic flow upstream a blunt body.