The disintegration process of a water jet issued from a 1.9mm-diameter nozzle into an otherwise quiescent atmosphere in microgravity was observed with a high-speed camera in order to compare to the corresponding conventional results for vertically downward issued water jets under normal gravity condition. The range of liquid Weber number is varied from zero to three, keeping the issued liquid flow laminar. Consistent with our prediction, the breakup lengths obtained in the microgravity experiments are shorter than those obtained in the laboratory experiments. In the microgravity experiment, no disintegration was observed in the final state unless the liquid Weber number exceeds unity, and the breakup length increases linearly from zero when the Weber number exceeds unity. This is significantly different from the behavior observed in the laboratory experiments because it is known that the breakup length exhibits a histerisis behavior between zero and unity Weber number. It is revealed that the histerisis behavior is caused by the effect of gravity. The mechanism how the breakup length is determined is also established on the basis of our proposed atomization theory.
The regenerative cooling combustion chamber of a liquid rocket engine is exposed to large temperature difference between the combustion gas and the coolant such as liquid hydrogen. It induces thermal stress, and strain is accumulated over cyclic firing tests in the chamber wall. To evaluate the strain and the deformation of chamber walls is important since the chamber life usually relates to such strain and deformation. The primary objective of the present study is to establish a method to obtain experimental data on strains and deformations for correlation with the numerical data. In this study, residual strains and radiographs of a combustion chamber were obtained by applying a neutron diffraction method and a neutron radiography. Furthermore, two-dimensional nonlinear finite element method (FEM) analyses were conducted to calculate the residual strain in the chamber wall. From data of strain measurements, the feasibility of a neutron diffraction method for a combustion chamber was shown because the data from a X-ray diffraction method and FEM analyses qualitatively corresponded with those from a neutron diffraction method. Concerning neutron radiography, a higher resolution was necessary to observe chamber wall deformation.
Carbon fiber-reinforced composites have been recently applied for engine fan blades, because of their high specific strength. In the design of the fan blade, the bird-strike impact is one of the greatest concerns, since impact-induced damage can lead to the engine stall. This study presented a numerical method to analyze the bird-strike impact as a soft-body impact on cantilevered composite panel. Especially, we coupled a stabilized dynamic contact analysis, which enables predicting impact force on the panel appropriately, with laminate damage analysis to predict the impact-induced progressive damage in the composite. This method was verified through the comparison with the experimental results. With the numerical method, we investigated the effect of impact condition, blade thickness and shape on the impact-induced damage in composite fan blade subjected to a bird strike. An intermediate blade thickness and a large blade curvature help improving the bird-striking impact resistance of the composite.
In rescue operations and emergency medical services, helicopters are frequently required to operate near the ground with obstacles such as buildings and sidewalls of highway. In this paper, numerical analysis of helicopter rotor hovering in close proximity to the ground with an obstacle is done by solving unsteady 3D compressible Euler equations with an overlapped grid system. The obstacle is simulated by a wall vertically set up on the ground. The parameters for numerical analysis are the rotor height and distance from the rotor-hub-center to the wall. The effects of combinations of these parameters on the flowfields around the rotor, inflow distributions on the rotor disc and behaviors of blade flapping motion are discussed. It is also clarified the cause that the helicopter rotor hovering in close proximity to the ground with a wall does not have the enough ground effect depending on the combinations of these parameters.