Kyoichi Ui

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.

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 .

Acoustic measurement of 1:42 scale booster and launch pad

This paper describes the acoustic measurement of the sub-scale booster and launch pad. The 1:42 scale solid propellant booster was settled over the launch pad model on a flat plate. Designed to deflect the hot and high speed jet plume, the launch pad model was expected to mitigate acoustic impact fed back toward the vehicle. The launch pad model plays a role in attenuating the sound due to the impingement of the plume and the deflector. To investigate the acoustic field with a different booster height, acoustic measurement was carried out. The measurement involved the conventional acoustic measurement and the sound source localization. The conventional measurement employed the near-field microphones around the booster model and the far-field microphones on an arc centered on the base of the launch pad. In the sound source localization, a phased array microphone system was settled to focus the deflector exit. The obtained acoustic data helped revise the design of the launch pad model.

Assessing Prediction and Reduction Technique of Lift-off Acoustics Using Epsilon Flight Data

Acoustic design of launch pad and prediction of full-scale acoustic environment are carried out by the numerical simulation and 1/42-scale model test for the Epsilon launch vehicle. Post-flight acoustic analysis of the Epsilon’s first flight is conducted. It is found that the acoustic level inside and outside the payload fairing satisfies the design requirement. The overall sound pressure level inside the payload fairing is achieved to be 132.3 dB without water injection system. Acoustic level outside the payload faring is reduced by 10 dB in compared with the former M-V launcher through the modification of the launch pad. The flight result reveals the effectiveness of the acoustic design methodology developed by the authors for acoustic attenuation at lift-off. Accuracy for predicting full-scale launch environment based on the results of the subscale model test and the numerical simulation is also assessed in this study.

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.

Post-flight acoustic analysis of Epsilon launch vehicle at lift-off

Acoustic level both inside and outside the fairing is measured at the first Epsilon Launch Vehicle (Epsilon-1). The obtained data shows time-varying fluctuation due to the ascent of the vehicle. Equivalent stationary duration for such non-stationary flight data is determined based on the procedure described in NASA HDBK-7005. The launch pad used by the former M-V launcher is modified for the Epsilon based on the Computational Fluid Dynamics (CFD) and 1/42-scale model tests. Although the launch pad is compact and any water injection system is not installed, 10 dB reduction in overall sound pressure level (OASPL) is achieved due to the modification for the Epsilon, comparing with the M-V. Acoustic level inside the fairing satisfies the design requirement. Acoustic design of the launch pad developed here is revealed to be effective. Prediction of the acoustics level based on the Computational Fluid Dynamics (CFD) and subscale testing is also investigated by comparing with the flight measurement.

Acoustic measurements of the Epsilon rocket at liftoff

Launch vehicles generate intense acoustic field caused by the enormous thrust power during liftoff, and this acoustic field leads to harmful payload vibration. Japan Aerospace Exploration Agency (JAXA) plans to launch a new solid propellant rocket, Epsilon, in 2013. This three-stage rocket utilizes a reliable first stage motor of the JAXA’s H-2 rocket, SRB-A. Since the SRB-A is expected to cause excessive acoustic load, a countermeasure was required to mitigate the acoustic feedback to the vehicle. Computational works proposed a launch pad structure to attenuate the Mach wave radiation from the plume, and the acoustic wave generated by the plume impinging to the flame deflector. In the previous ASA conference, the authors introduced scale model tests using 1:42 scale rocket motors and the launch pad models. The scale model tests clarified the acoustic benefit of the launch pad structure. The tested geometry of the launch pad structure was adopted to the full-scale structure. Acoustic measurements are plan...

Scale model tests for acoustic prediction and reduction of epsilon launch vehicle at lift-off

Test campaign using 1/42-scale model is conducted to predict acoustic level of the Epsilon launch vehicle at lift-off. Analogy between sub-scale and full-scale tests is investigated to obtain the same feature of the acoustics. Methodology to correct the measured data obtained in the sub-scale test for predicting the full-scale environment is also clarified in this study. The acoustic results around the practical shape of the launch-pad are successfully obtained. The parametric studies are conducted to reduce noise level in the test campaign with the help of the numerical simulation, and the effect for noise reduction is observed up to 5dB in 1/1-octaveband SPL.

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.