科创中国

Current researches show that mechanical deformation of seal ring face makes fluid film clearance decrease at high pressure side, thus a divergent clearance is formed and face wear occurs more seriously at the high pressure side than that on the low pressure side. However, there is still lack of published experimental works enough to prove the theoretical results. In this paper, a spiral groove dry gas seal at high pressures is experimentally investigated so as to prove the face wear happened at the high pressure side of seal faces due to the face mechanical deformation, and the wear behavior affected by seal ring structure is also studied. The experimental results show that face wear would occur at the high pressure side of seal faces due to the deformation, thus the leakage and face temperature increase, which all satisfies the theoretical predictions. When sealed pressure is not less than 5 MPa, the pressure can provide enough opening force to separate the seal faces. The seal ring sizes have obvious influence on face wear. Face wear, leakage and face temperature of a dry gas seal with the smaller cross sectional area of seal ring are less than that of a dry gas seal with bigger one, and the difference of leakage rate between these two sizes of seal face width is in the range of 24%–25%. Compared with the effect of seal ring sizes, the effect of secondary O-ring seal position on face deformation and face wear is less. The differences between these two types of dry gas seals with different secondary O-ring seal positions are less than 5.9% when the rotational speed varies from 0 to 600 r/min. By linking face wear and sealing performance changes to the shift in mechanical deformation of seal ring, this research presents an important experimental method to study face deformation of a dry gas seal at high pressures.

The T-junction model of engine exhaust manifolds significantly influences the simulation precision of the pressure wave and mass flow rate in the intake and exhaust manifolds of diesel engines. Current studies have focused on constant pressure models, constant static pressure models and pressure loss models. However, low model precision is a common disadvantage when simulating engine exhaust manifolds, particularly for turbocharged systems. To study the performance of junction flow, a cold wind tunnel experiment with high velocities at the junction of a diesel exhaust manifold is performed, and the variation in the pressure loss in the T-junction under different flow conditions is obtained. Despite the trend of the calculated total pressure loss coefficient, which is obtained by using the original pressure loss model and is the same as that obtained from the experimental results, large differences exist between the calculated and experimental values. Furthermore, the deviation becomes larger as the flow velocity increases. By improving the Vazsonyi formula considering the flow velocity and introducing the distribution function, a modified pressure loss model is established, which is suitable for a higher velocity range. Then, the new model is adopted to solve one-dimensional, unsteady flow in a D6114 turbocharged diesel engine. The calculated values are compared with the measured data, and the result shows that the simulation accuracy of the pressure wave before the turbine is improved by 4.3% with the modified pressure loss model because gas compressibility is considered when the flow velocities are high. The research results provide valuable information for further junction flow research, particularly the correction of the boundary condition in one-dimensional simulation models.

Natural frequency characteristics of a thin-walled multiple layered cylindrical shell under lateral pressure are studied.The multiple layered cylindrical shell configuration is formed by three layers of isotropic material where the inner and outer layers are stainless steel and the middle layer is aluminum.The multiple layered shell equations with lateral pressure are established based on Love's shell theory.The governing equations of motion with lateral pressure are employed by using energy functional and applying the Ritz method.The boundary conditions represented by end conditions of the multiple layered cylindrical shell are simply supported-clamped(SS-C),free-clamped(F-C)and simply supported-free(SS-F).The influence of different lateral pressures,different thickness to radius ratios,different length to radius ratios and effect of the asymmetric boundary conditions on natural frequency characteristics are studied.It is shown that the lateral pressure has effect on the natural frequency of multiple layered cylindrical shell and causes the natural frequency to increase.The natural frequency of the developed multilayered cylindrical shell is validated by comparing with those in the literature.The proposed research provides an effective approach for vibration analysis shell structures subjected to lateral pressure with an energy method.

The mechanical properties and microstructure evolution of cold-deformed CrMnN austenitic stainless steel annealed in a temperature ranging from 50 ℃ to 650 ℃ for 90 min and at 550 ℃ for different time were investigated by tensile test, micro hardness test, and Transmission Electron Microscope (TEM). The steel was strengthened when it got annealed at temperatures ranging from 100 ℃ to 550 ℃, while it was softened when it got annealed at temperatures ranging from 550 ℃ to 650 ℃. Annealing temperature had stronger effect on mechanical properties than annealing time. TEM observations showed that nano-sized precipitates formed when the steel was annealed at 150 ℃ for 90 min, but the size and density of precipitates had no noticeable change with annealing temperature and time. Recrystallization occurred when the steel was annealed at temperatures above 550 ℃ for 90 min, and its scale increased with annealing temperature. Nano-sized annealing twins were observed. The mechanisms that controlled the mechanical behaviors of the steel were discussed.

The competition of surface and subsurface crack initiation induced failure is critical to understand very high cycle fatigue(VHCF)behavior,which necessitates the elucidation of the underlying mechanisms for the transition of crack initiation from surface to interior defects.Crack initiation potential in materials containing defects is investigated numerically by focusing on defect types,size,shape,location,and residual stress influences.Results show that the crack initiation potency is higher in case of serious property mismatching between matrix and defects,and higher strength materials are more sensitive to soft inclusions(elastic modulus lower than the matrix).The stress localization around inclusions are correlated to interior crack initiation mechanisms in the VHCF regime such as inclusion-matrix debonding at soft inclusions and inclusion-cracking for hard inclusions(elastic modulus higher than the matrix).It is easier to emanate cracks from the subsurface pores with the depth 0.7 times as large as their diameter.There exists an inclusion size independent region for crack incubation,outside which crack initiation will transfer from the subsurface soft inclusion to the interior larger one.As for elliptical inclusions,reducing the short-axis length can decrease the crack nucleation potential and promote the interior crack formation,whereas the long-axis length controls the site of peak stress concentration.The compressive residual stress at surface is helpful to shift crack initiation from surface to interior inclusions.Some relaxation of residual stress can not change the inherent crack initiation from interior inclusions in the VHCF regime.The work reveals the crack initiation potential and the transition among various defects under the influences of both intrinsic and extrinsic factors in the VHCF regime,and is helpful to understand the failure mechanism of materials containing defects under long-term cyclic loadings.

The remanufacturing blanks with cracks were considered as irreparable. With utilization of detour effect and Joule heating of pulsed current, a technique to arrest the crack in martensitic stainless steel FV520B is developed. According to finite element theory, the finite element(FE) model of the cracked rectangular specimen is established firstly. Then, based on electro-thermo-structure coupled theory, the distributions of current density, temperature field, and stress field are calculated for the instant of energizing. Furthermore, the simulation results are verified by some corresponding experiments performed on high pulsed current discharge device of type HCPD-I. Morphology and microstructure around the crack tip before and after electro pulsing treatment are observed by optical microscope(OM) and scanning electron microscope(SEM), and then the diameters of fusion zone and heat affected zone(HAZ) are measured in order to contrast with numerical calculation results. Element distribution, nano-indentation hardness and residual stress in the vicinity of the crack tip are surveyed by energy dispersive spectrometer(EDS), scanning probe microscopy(SPM) and X-ray stress gauge, respectively. The results show that the obvious partition and refined grain around the crack tip can be observed due to the violent temperature change. The contents of carbon and oxygen in fusion zone and HAZ are higher than those in matrix, and however the hardness around the crack tip decreases. Large residual compressive stress is induced in the vicinity of the crack tip and it has the same order of magnitude for measured results and numerical calculation results that is 100 MPa. The relational curves between discharge energies and diameters of the fusion zone and HAZ are obtained by experiments. The difference of diameter of fusion zone between measured and calculated results is less than 18.3%. Numerical calculation is very useful to define the experimental parameters. An effective method to prevent further extension of the crack is presented and can provide a reference for the compressor rotor blade remanufacturing.

In the mixed-flow pump design,the shape of the flow passage can directly affect the flow capacity and the internal flow,thus influencing hydraulic performance,cavitation performance and operation stability of the mixed-flow pump.However,there is currently a lack of experimental research on the influence mechanism.Therefore,in order to analyze the effects of subtle variations of the flow passage on the mixed-flow pump performance,the frustum cone surface of the end part of inlet contraction flow passage of the mixed-flow pump is processed into a cylindrical surface and a test rig is built to carry out the hydraulic performance experiment.In this experiment,parameters,such as the head,the efficiency,and the shaft power,are measured,and the pressure fluctuation and the noise signal are also collected.The research results suggest that after processing the inlet flow passage,the head of the mixed-flow pump significantly goes down;the best efficiency of the mixed-flow pump drops by approximately 1.5%,the efficiency decreases more significantly under the large flow rate;the shaft power slightly increases under the large flow rate,slightly decreases under the small flow rate.In addition,the pressure fluctuation amplitudes on both the impeller inlet and the diffuser outlet increase significantly with more drastic pressure fluctuations and significantly lower stability of the internal flow of the mixed-flow pump.At the same time,the noise dramatically increases.Overall speaking,the subtle variation of the inlet flow passage leads to a significant change of the mixed-flow pump performance,thus suggesting a special attention to the optimization of flow passage.This paper investigates the influence of the flow passage variation on the mixed-flow pump performance by experiment,which will benefit the optimal design of the flow passage of the mixed-flow pump.

The aerodynamic braking is a clean and non-adhesion braking, and can be used to provide extra braking force during high-speed emergency braking. The research of aerodynamic braking has attracted more and more attentions in recent years. However, most researchers in this field focus on aerodynamic effects and seldom on issues of position control of the aerodynamic braking board. The purpose of this paper is to explore position control optimization of the braking board in an aerodynamic braking prototype. The mathematical models of the hydraulic drive unit in the aerodynamic braking system are analyzed in detail, and the simulation models are established. Three control functions-constant, linear, and quadratic-are explored. Two kinds of criteria, including the position steady-state error and the acceleration of the piston rod, are used to evaluate system performance. Simulation results show that the position steady state-error is reduced from around 12–2 mm by applying a linear instead of a constant function, while the acceleration is reduced from 25.71–3.70 m/s2 with a quadratic control function. Use of the quadratic control function is shown to improve system performance. Experimental results obtained by measuring the position response of the piston rod on a test-bench also suggest a reduced position error and smooth movement of the piston rod. This implies that the acceleration is smaller when using the quadratic function, thus verifying the effectiveness of control schemes to improve to system performance. This paper proposes an effective and easily implemented control scheme that improves the position response of hydraulic cylinders during position control.

The methods of improving the dynamic performance of high speed on/off solenoid valve include increasing the magnetic force of armature and the slew rate of coil current, decreasing the mass and stroke of moving parts. The increase of magnetic force usually leads to the decrease of current slew rate, which could increase the delay time of the dynamic response of solenoid valve. Using a high voltage to drive coil can solve this contradiction, but a high driving voltage can also lead to more cost and a decrease of safety and reliability. In this paper, a new scheme of parallel coils is investigated, in which the single coil of solenoid is replaced by parallel coils with same ampere turns. Based on the mathematic model of high speed solenoid valve, the theoretical formula for the delay time of solenoid valve is deduced. Both the theoretical analysis and the dynamic simulation show that the effect of dividing a single coil into N parallel sub-coils is close to that of driving the single coil with N times of the original driving voltage as far as the delay time of solenoid valve is concerned. A specific test bench is designed to measure the dynamic performance of high speed on/off solenoid valve. The experimental results also prove that both the delay time and switching time of the solenoid valves can be decreased greatly by adopting the parallel coil scheme. This research presents a simple and practical method to improve the dynamic performance of high speed on/off solenoid valve.

With the increasing noise pollution,low noise optimization of centrifugal pimps has become a hot topic.However,experimental study on this problem is unacceptable for industrial applications due to unsustainable cost.A hybrid method that couples computational fluid dynamics(CFD)with computational aeroacoustic software is used to predict the flow-induced noise of pumps in order to minimize the noise of centrifugal pumps in actual projects.Under Langthjem's assumption that the blade surface pressure is the main flow-induced acoustic source in centrifugal pumps,the blade surface pressure pulsation is considered in terms of the acoustical sources and simulated using CFX software.The pressure pulsation and noise distribution in the near-cutoff region are examined for the blade-passing frequency(BPF)noise,and the sound pressure level(SPL)reached peaks near the cutoff that corresponded with the pressure pulsation in this region.An experiment is performed to validate this prediction.Four hydrophones are fixed to the inlet and outlet ports of the test pump to measure the flow-induced noise from the four-port model.The simulation results for the noise are analyzed and compared with the experimental results.The variation in the calculated noise with changes in the flow agreed well with the experimental results.When the flow rate was increased,the SPL first decreased and reached the minimum near the best efficient point(BEP);it then increased when the flow rate was further increased.The numerical and experimental results confirmed that the BPF noise generated by a blade-rotating dipole roughly reflects the acoustic features of centrifugal pumps.The noise simulation method in current study has a good feasibility and suitability,which could be adopted in engineering design to predict and optimize the hydroacoustic behavior of centrifugal pumps.