Kota Fukuda

Effect of Deflector Shape on Acoustic Field of Launch Vehicle at Lift-off

As part of the studies on the advanced solid rocket in JAXA, numerical simulations were carried out to investigate the effect of the flame deflector (FD) shape on the acoustic level of the launch vehicle at lift-off. The results indicate that there are mainly two types of acoustic sources; 1) “impingement noise” due to the interaction of the exhaust plume and FD, and 2) Mach wave generated by the flapping motion of the plume flowing over the FD. Since the impingement noise propagates directly to the vehicle, the acoustic level of the vehicle is dominated by the impingement noise. Based on the knowledge obtained here, it is found that the initial inclination angle of the FD should be steep to reduce the impingement noise. Besides, it also turns out that the FD is desirable to have a curved surface both for reducing the size of the FD and for preventing another impingement noise caused by the rapid change of the FD contour.

Acoustic Measurement and Prediction of Solid Rockets in Static Firing Tests

Acoustic measurements are executed in two series of static-firing tests of a solid rocket motor. The obtained data are quantitatively compared with calculation results of an empirical prediction method, NASA SP-8072 and CFD. According to the results, the NASA SP-8072 overestimates the sound pressure levels at the 20° and 35° points from the jet axis in the far field, although the SPLs at other measured points are reasonably predicted. On the other hand, the CFD calculation can clearly explain the generation and propagation mechanism of the acoustic wave and reasonably predict the SPLs at all the measured points. From the results, it is confirmed that the prediction accuracy of the CFD calculation is within 5 [dB] in overall sound pressure level, which is within the experimental uncertainty involved in the measured data, and the CFD is effective for the prediction of both the near and the far field acoustics generated from the rocket motors.

A Numerical Scheme Based on an Immersed Boundary Method for Compressible Turbulent Flows with Shocks: Application to Two-Dimensional Flows around Cylinders

A computational code adopting immersed boundary methods for compressible gas-particle multiphase turbulent flows is developed and validated through two-dimensional numerical experiments. The turbulent flow region is modeled by a second-order pseudo skew-symmetric form with minimum dissipation, while the monotone upstream-centered scheme for conservation laws (MUSCL) scheme is employed in the shock region. The present scheme is applied to the flow around a two-dimensional cylinder under various freestream Mach numbers. Compared with the original MUSCL scheme, the minimum dissipation enabled by the pseudo skew-symmetric form significantly improves the resolution of the vortex generated in the wake while retaining the shock capturing ability. In addition, the resulting aerodynamic force is significantly improved. Also, the present scheme is successfully applied to moving two-cylinder problems.

A Simple Immersed Boundary Method for Compressible Flow Simulation around a Stationary and Moving Sphere

This study is devoted to investigating a flow around a stationary or moving sphere by using direct numerical simulation with immersed boundary method (IBM) for the three-dimensional compressible Navier-Stokes equations. A hybrid scheme developed to solve both shocks and turbulent flows is employed to solve the flow around a sphere in the equally spaced Cartesian mesh. Drag coefficients of the spheres are compared with reliable values obtained from highly accurate boundary-fitted coordinate (BFC) flow solver to clarify the applicability of the present method. As a result, good agreement was obtained between the present results and those from the BFC flow solver. Moreover, the effectiveness of the hybrid scheme was demonstrated to capture the wake structure of a sphere. Both advantages and disadvantages of the simple IBM were investigated in detail.

Examination of Sound Suppression by Water Injection at Lift-off of Launch Vehicles

Analytical investigation of noise suppression effect of water injection to exhaust plume from rocket motors was carried out. The results showed acoustic absorption by water droplets, acoustic scatter by water droplets, absorption through air, and water curtain effect increase as frequency becomes high. It was also confirmed that acoustic absorption by water droplets has the most significant effects among the four effects. Furthermore, steady 2D-axisymmetric Reynolds-Averaged Navier-Stokes (RANS) simulations of a supersonic free jet were carried out in order to evaluate reduction of jet energy due to water injection. The reduction of the acoustic source strength along the jet axis was evaluated considering the difference of ρk value between with and without water injection. The far field sound power level (SPL) was analyzed using an empirical prediction method, NASA SP-8072 and compared to sub-scale motor test data. The strength of the acoustic source power along the jet axis was set based on the reduction rate of the ρk value due to water injection and the propagation to the far filed points was analyzed based on the NASA SP-8072. The results showed that the water injection effect can be reasonably evaluated by using both the analytical prediction methodology and the evaluation methodology of reduction of the jet energy based on the change of ρk .

Analysis of the Temperature Ratio Effects on the Flow Properties of the Low Reynolds and High Mach number Flow around a Sphere

In this study, direct numerical simulation of the flow around a sphere at the high Mach number and the low Reynolds number condition is carried out in order to investigate the flow properties. The three-dimensional compressible Navier-Stokes equations are solved on boundary fitted coordinate system. It is confirmed to have sufficient accuracy from the results of the previous study. Analyses are performed at the Reynolds number of between 50 and 300, the freestream Mach number of between 0.3 and 2.0, and the temperature ratio of the sphere surface and freestream of between 0.5 and 2.0. As the results, we clarified the following points: 1) the freestream Reynolds number and the temperature ratio influence the flow properties, 2) the effect of the temperature ratio can be summarized by the effective Reynolds number that is a newly proposed parameter.

Acoustic design of launch pad for advanced solid rocket.

In the mission of the Advanced Solid Rocket studied in JAXA, the launch‐pad is required to improve the operation performance as well as to reduce the cost. While, exhaust plume from the solid booster generates severe acoutic wave so that decrease in the acoustic level at lift‐off is also an important design issue. Preliminary trade‐off analysis is peformend by using computational fluid dynamics. Major noise sources such as the Machwave and the impingement noise and their correlation with the vehicle’s altitude are revealed. The knowledge of the acoustic characteristics gives us idea how to decrease the acoustic level within the mission requirements. Based on the configuration found in the numerical study, subscale test using 1/43 scale mock‐up is planned to ensure the acoustic level around the vehicle.

Direct Numerical Simulation of Shock Waves Passed by Multiple Particles by Using Immersed Boundary Method

A flow containing multiple particles and the shock wave is investigated by the direct numerical simulation with immersed boundary method. The shock Mach number and the Reynolds numbers of particle behind the shock wave are set to be 1.5 to 2.0 and 300 to 600, respectively. The comparison of the present results with one-dimensional simulation results, shows good agreement. From the results, we clarified characteristic flow structure at different shock Mach and Reynolds number. The turbulence kinetic energy was enhanced from the vortex structure in the wake of particles for the high Reynolds number case. The drag coefficient from the present simulation and the previous prediction models shows almost the same values at Mach number 1.5. At Mach number 2.0, however, discrepancy is obtained for the drag coefficient between the present flow simulation and the previous prediction models.

Laser Ablation Thrusters for Atmospheric Flight Applications

In this study, authors propose direct focusing of repetitive high-power laser pulses on an arbitrary surface of the vehicle in atmosphere, in which a blast wave is generated at each pulse and pushes the vehicle on the surface inducing an impulse or thrust vector. A fundamental investigation was conducted on interaction of a focused high-power laser pulse, or blast wave, and the surface with arbitrary shape. Numerical simulation on characteristics of impulse, or thrust, vector generation on the surface was conducted. As the first step of the simulation, for simplicity, some fundamental shapes of the surface, or a vehicle, were assumed, which were planar and semicircular bodies, and shock-surface interactions were investigated. As results, a deeper convex vehicle showed largest vertical impulses, and a shallower convex vehicle showed smallest horizontal impulses.

Acoustic measurement in the static firing tests of solid rocket motors.

Acoustic management is essential for establishing a reliable and cost‐competitive rocket system. A solid propellant motor during its lift‐off imposes high levels of pressure and vibration on the fairing of the rocket, sometimes leading to crucial damage of the payload. One approach to resolve this problem is to decrease the sound sources caused by high‐speed plume of the rocket booster. Japan Aerospace Exploration Agency (JAXA), aiming at the advanced solid rocket, started computational prediction that helps design a launch‐pad with less acoustic impact. For validating the computation codes and modeling the acoustic characteristics, the experimental acoustic data of solid rocket motors have long been desired. Fortunately, we had opportunities of the ground firing tests with several motors. In this presentation, the acoustic measurement including the sensors, the set‐up, and the data reduction carried out in these tests will be discussed.