Novel resonance stability criterion for the 2D magnetically levitated servo-proportional valve

The leakage of the pilot stage of the 2D valve mainly depends on the size of its initial opening. According to the Routh criterion, the pilot stage of the two-dimensional magnetically levitated servo-proportional valve (2D-MSP valve) needs to be designed to have certain positive values to increase the damping ratio to improve valve stability, which leads to the leakage flow representing a non-negligible power loss. In order to reduce leakage flow and achieve goal of energy saving, this paper presents a novel resonance stability criterion by considering nonlinear characteristics of the fluid dynamic system. First, the 2D-MSP valve is regarded as a three-way valve-controlled differential cylinder system. Based on the frequency response of the resonance state, the energy conservation method is used to solve the flow “backfilling” area, the motion equation of the cylinder piston (valve spool displacement) and the pressure waveform of the sensing chamber under different opening and pressure amplitude ratio. Then, the analytical expression of the resonance peak amplitude is obtained and the resonance stability criterion is deduced. The result is compared with the Routh stability criterion, which illustrates that the positive openings of the pilot stage can be reduced to one-third of the original value. The prototype valve is then designed and manufactured based on the resonance stability criterion. The dynamic and static characteristics under different system pressures are measured. Experimental results show that the prototype valve is an over-damped system without any overshoot, which has excellent working stability, and its static and dynamic performance can meet the demands of the industry servo-proportional control system. The research work validates the effectiveness of the proposed resonance stability criterion.

Broadband Design of Acoustic Metasurfaces for the Stabilization of a Mach 4 Boundary Layer Flow

A piecewise acoustic metasurface is designed to suppress the first mode while marginally amplifying the Mack second mode in a Mach 4 flat-plate boundary layer (BL) flow. The results of linear stability theory (LST) and the eN method demonstrate the stabilization effect and transition delay performance, respectively. However, the direct numerical simulation (DNS) results indicate that the designed broadband acoustic metasurface actually weakly excites the first mode with a slightly larger fluctuating pressure amplitude at the surface, which is in contrast to the analysis of LST. The discrepancies are found to lie in the ‘roughness’ effect caused by the recirculation zones inside the microslits and the alternating expansion and compression waves induced at the slit edges, which significantly amplifies the first mode. For further clarification of the competitive mechanism between the acoustic stabilization and ‘roughness’ destabilization effects of metasurfaces on the first mode, a carefully designed metasurface is installed at the maximum growth rate region, which excites the first mode on the metasurface but inhibits its development downstream.

Cavitation threshold pressure of focused ultrasound observed with sonochemiluminescence

Spatial distribution of sonochemiluminescence (SCL) from an argon-saturated luminol solution was measured in a focused sound field at 1 MHz in a standing-wave configuration. The SCL distribution was confined to pre-focal region at acoustic powers lower than 0.9 W, and was not located at the focus but at a few mm pre-focal side at a threshold for SCL inception. The threshold pressure amplitude for SCL inception was 3.6 atm at the focus, which value was obtained with a background-oriented schlieren method. The method is based on the broadening of multiple slits due to an optical deflection caused by ultrasound, and the broadening width measured provides an acoustic pressure amplitude. A qualitative image of the focused sound field was also obtained.

Research of Pressure Fluctuation with Experiment and Numerical Simulation for Dredging Pump

In order to reveal the dredge pump flow instability characteristics, the cavitation and pressure fluctuation in experimental study are carried out, the pressure fluctuation frequency domain and time domain characteristics of three different position inside the volute are analyzed. The results showed that, before cavitation, the main frequency at different positions at different flow rates is 1 times the main frequency of the blade. The fluctuation amplitude near the volute tongue and diffusion section is slightly larger than that at other positions. Before cavitation, the fluctuation amplitude at the same position off design flow is slightly higher than that near the design flow. Cavitation has little influence on the main frequency of the pressure fluctuation. After cavitation, the pressure fluctuation amplitude in the low flow point and the position of the volute tongue under each condition has little change, but cavitation aggravates the pressure fluctuation in the other conditions. Besides, the comparison between simulation and experiment results shows the dredge pump performance curve is in good agreement with the simulation curve, and the simulation results of pressure amplitude at different positions are basically consistent with the experiment results, which verifies the reliability of the numerical simulation method.

Numerical Analysis of the Aerodynamic Characteristics of the Open Line Intersection of Fast Freight Train with the Speed of 160 km/h

With the increase of the speed of fast freight train, the aerodynamic effect of freight train in open-line intersection is more obvious. However, at present, there are many domestic researches on the aerodynamic characteristics of high-speed train open-line intersection, and almost no researches on fast freight train. Therefore, it is of great significance to study the aerodynamic characteristics of open line intersection of fast freight train in order to improve the safe operation of freight train in China. Based on the theory of computational fluid dynamics and finite volume method, uses FLUENT software to numerically calculate the three-dimensional, unsteady, compressible and turbulent flow fields in open line intersection of fast freight train at different speeds. The calculations results indicate that: when two freight trains meet, the amplitude of the pressure wave at the intersection side is the largest and the closer to the train bottom, the greater the amplitude of the pressure wave. The pressure amplitude of the bottom measuring point is 34.09% higher than that of the top measuring point. When two cars intersect at the same speed, the higher the speed, the greater the pressure amplitude and the pressure amplitude is proportional to the square of the speed. The fitting formula is: ΔP = cV2 ; When two trains intersect at different speeds, the impact on freight train with lower speed is greater than higher one.

Plasma channel dynamics in sub- and microsecond discharges in water

Simulation results of a fast electric discharge and a strong acoustic wave in the water is performed. A theoretical model of a high-current plasma channel is presented. The model accounts for the energy ratio between the input electric power and the plasma channel conductivity, and adiabatic expansion mechanism of this channel in water. It allows you to calculate the dynamics of the expansion of the channel and the generation of a radially diverging acoustic wave. The presented study makes it possible to estimate the probable parameters of the phenomenon: when electric energy is introduced into the channel, its expansion velocity reaches 1.9 km/s, electrons number density in the plasma is up to 2·1020 cm−3. In this case, a strong acoustic wave propagates with a sonic speed (~ 1500 m/s), and the pressure amplitude in the vicinity of the plasma channel can reach 200 MPa. The stability of the model in relation to variations in the initial task parameters has been analyzed. The calculated data for the acoustic wave are in good agreement with the measurements.

DEVELOPMENT OF A LIFETIME PRESSURE SENSITIVE PAINT PROCEDURE FOR HIGH-PRESSURE VANE TESTING

Optical measurements based on fast response Pressure Sensitive Paint (PSP) provide enhanced spatial resolution of the pressure field. This paper presents lifetime PSP at 20 kHz, with precise calibrations, and results from a demonstration in an annular vane cascade. The laser lifetime PSP methodology is first evaluated in a linear wind tunnel with a converging-diverging nozzle followed by a wavy surface. This test section is fully optically accessible with maximum modularity. A data reduction procedure is proposed for the PSP calibration, and optimal pixel binning is selected to reduce the uncertainty. In the annular test section, laser lifetime PSP was used to measure the time-averaged static pressure field on a section of the suction surface of a high-pressure turbine vane. Tests were performed at engine representative conditions in the Purdue Big Rig for Annular Stationary Turbine Analysis module at the Purdue Experimental Turbine Aerothermal Lab. The 2-D pressure results showed a gradual increase of pressure across the spanwise and flow directions, corroborated with local static pressure taps and computational results. The variation in PSP thickness was measured as a contribution to the uncertainty. The discrete Fourier transform of the unsteady pressure signal showed increased frequency content in wind-on compared to wind-off conditions at the mid-span and 30% span. Compared to the mid-span, the hub end wall region had an increase in frequencies and pressure amplitude. This result was anticipated given the expected presence of secondary flow structures at the near hub region.

CFD Modeling and Performance Analysis of a Thermoacoustically Driven Thermoacoustic Refrigerator

Although thermoacoustic devices comprise simple components, the design of these machines is very challenging. In order to predict the behavior and optimize the performance of a thermoacoustic refrigerator driven by a standing-wave thermoacoustic engine, considering the changes in geometrical parameters, two analogies have been presented in this paper. The first analogy is based on CFD analysis where a 2D model is implemented to investigate the influence of stack parameters on the refrigerator performance, to analyze the time variation of the temperature gradient across the stack, and to examine the refrigerator performance in terms of refrigeration temperature. The second analogy is based on the use of an optimization algorithm based on the simplified linear thermoacoustic theory applied for designing thermoacoustic refrigerators with different stack parameters and operating conditions. Simulation results show that the engine produced a high-powered acoustic wave with a pressure amplitude of 23[Formula: see text]kPa and a frequency of 584[Formula: see text]Hz and this wave applies a temperature difference across the refrigeration stack with a cooling temperature of 292.8[Formula: see text]K when the stacks are positioned next to the pressure antinode. The results from the algorithm give the ability to design any thermoacoustic refrigerator with high performance by picking the appropriate parameters.

Theoretical model and dynamic wave-amplification effect of the high intensity Helmholtz sound source

Helmholtz sound source consists of Helmholtz resonator and speaker and belongs to a new type of high-intensity sound source. It has potential industrial advantage in the aerodynamic acoustic application for the large amplitude wave. Based on the lumped parameter principle of acoustic impedance, an acoustic theoretical model is suggested. The model reveals the amplification regulation of the sound source on the acoustic wave. Through the acoustic theoretical computation, a dynamic amplification and an amplification limitation are analyzed. The wave-amplification effect attributes to the parameter regulation of the macro, micro, and dynamic-varied sizes of the sound source. The repetitive motion of the vibrating membrane of speaker causes three working states of balance, squeeze, and stretch. The three states act as specific boundary conditions and demonstrate as three different theoretical curves. The theoretical boundary curves codetermine an experimental curve, which essentially limits the practical amplification effect. Nevertheless, the amplification gain of sound pressure amplitude reaches up to 1.8 times, and the potential maximum amplitude reaches up to 3600 Pa (164 dB). The two quantitative characteristics indicate the maximum capability of the sound source on wave-amplification effect. The control sensitivity of the complicated impedance parameters on wave amplification is 0.26 Pa/Hz. The acoustic theoretical model is valuable in the series aspects of the industrial design, manufacture, and application of the sound source. Especially, the theoretical innovation lays the foundation of solid to these aspects.