Simulation and verification of measurement system for deep-sea pressure and its small fluctuation pressure

Combined pressure measuring system (CPMS), which is mainly used for measuring deep-sea larger pressure and its small fluctuation pressure, is studied. First, the working principle of the CPMS is introduced. Second, the mathematical model of the CPMS is established. Third, the influence of the cross-sectional area of the piston, the equivalent mass of the piston, the diving speed, the cross-sectional diameter of the compensator piston, the air content of the liquid medium, and the small fluctuation pressure on the measurement performance of the CPMS is analyzed using the simulation model. Then, the design principle of the system is summarized. Finally, the test platform is built. The results show that the dynamic pressure is not more than 0.025 bar when the pressure change speed is 0.2 bar/s, the pressure is 2.8 × 10−3 bar under 20 bar, thereby verifying the validity and accuracy of the measurement method and providing theoretical basis and reference for the design and optimization of the measurement system.

The suppression of hydrodynamic noise from underwater cavities by the change of back wall chamfer

When underwater vehicles are sailing, high hydrodynamic noise will be generated through the opening cavities due to the interaction of the surface and the fluids. In the paper, we had tested different forms of back wall chamfer by numerical calculation based on the method of large eddy simulation, to control the impact of the eddy and break the flow at the trailing edge of the cavity, which is with the dimension of 100mm wide, 120mm high and 100mm long. The angle and shape of the trailing edge chamfer are changed to control the flow of the cavity. We had also investigated the effect of hydrodynamic noise suppression through the simulation, which is based on the method of Lighthill’s acoustic analogy. The results show that the change of back wall chamfer can stabilize the movement of the eddies inside the cavity and reduce the fluctuation pressure at the trailing edge of the cavity. The suppression of flow-induced noise can be up to 5 dB, if the back-wall chamfer is with the airfoil surface and the angle of back wall chamfer is properly designed.

Aerodynamic Noise Reduction Analysis in High-Speed Train Cab

In order to reduce aerodynamic noise in high-speed train cab,the SEA model of cab is established. The fluctuation pressures from train head surface are calculated by large eddy simulation method. Using fluctuation pressure as excitation force, power flow caused by airflow among sub-systems of SEA model of cab is obtained. Two schemes are put forward to reduce the aerodynamic noise in cab, namely interior decoration modification and windowpane thickness increase. The results show that when a layer of splint with 0.01 m thickness, 0.5 loss factor is added to the original decoration in cab, the overall sound pressure level (SPL) at driver head location will reduce 1.23 dB(A). When the cab windowpane thickness is increased to 5 mm from 4 mm, the overall SPL at the driver head location will reduce 0.87 dB(A).

Wind Tunnel Study on a Missile with Forward-Facing Cavity in Supersonic Flow

A forward-facing cavity will be composed of the components of a scramjet from inlet to combustion chamber which has a uncovered inlet before the separation of the booster. Longitudinal oscillations are generated within the cavity under some certain flow conditions. Strong oscillations may damage the components of the scramjet, or induce bow-shock oscillations which may cause unsteady loads on the missile and affect the performance of the aerodynamical characteristics. An experimental study of missile model with a scramjet was conducted in a transonic wind tunnel. The characteristics of cavity flow were researched by both the dynamic force measurement and the fluctuation pressure measurement. In the experiments the oscillations within the cavity and the bow-shock in front of the inlet interacted. The oscillations of cavity flow and bow-shock affected the fluctuation pressure and the aerodynamical characteristics of missile remarkably. The amplitude of axial force was higher than the normal force's. The RMS of the fluctuation pressure of some measured place inside the scramjet reached a quarter of the total pressure, and the amplitude of the fluctuation reached half of the total pressure. Those might threaten the safety of the structure of the scramjet.