Large-scale Vacuum Vessel Design and Finite Element Analysis

The vacuum plume effects experimental system (PES) is the first experimental system designed to study the effects of vacuum plume in China. The main equipment, a vacuum chamber of 5.5 m in diameter and 12.8 m in length, and structure design of hinged door are described. The finite element method (FEM) is adopted to analyze the static strength and stability of the PES vacuum chamber. It is demonstrated that the static strength and stability are qualified. For the 5.5 m diameter vacuum chamber door, three design schemes are put forward. After comparisons are made, the single-axis-double-pin hinged door is selected. The FEM is applied to checking its static strength as well as distortions. The results show that the door’s distortion and displacement change mainly due to the gravity of the door which leads to its sinking. The calculated displacement is less than 7.8 mm, while the actual measurement is 5 mm. The single-axis-double-pin hinged door mechanism completely satisfies the design requirements. This innovative structure can be introduced as a reference for the design of large-scale hinged doors.     

Effect of boundary conditions on downstream vorticity from counter-rotating swirlers

Particle image velocimetry(PIV) is utilized to measure the non-reacting flow field in a reflow combustor with multiple and single swirlers. The velocity field, vortex structure and total vorticity levels are experimentally obtained using two different boundary conditions, representing a single confined swirler and multiple swirlers in an annular combustor. The influence of the boundary conditions on the flow field at several locations downstream of the swirlers is experimentally investigated, showing that the central vortex in the multi-swirler case is more concentrated than in the single-swirler case. The vorticity of the central vortex and average cross-sectional vorticity are relatively low at the swirler outlet in both cases. Both of these statistics gradually increase to the maximum values near 20 mm downstream of the swirler outlet, and subsequently decrease. It is also found that the central vortex in the multi-swirler case is consistently greater than the single-swirler case. These results demonstrate the critical influence of boundary conditions on flow characteristic of swirling flow, providing insight into the difference of the experiments on testbed combustor and the full-scale annular combustors.     

Experimental investigation of surface roughness effects on flow behavior and heat transfer characteristics for circular microchannels

This paper experimentally investigates the effect of surface roughness on flow and heat transfer characteristics in circular microchannels. All test pieces include 44 identical, parallel circu-lar microchannels with diameters of 0.4 mm and 10 mm in length. The surface roughness of the microchannels is Ra=0.86, 0.92, 1.02 lm, and the Reynolds number ranges from 150 to 2800. Results show that the surface roughness of the circular microchannels has remarkable effects on the performance of flow behavior and heat transfer. It is found that the Poiseuille and Nusselt num-bers are higher when the relative surface roughness is larger. For flow behavior, the friction factor increases consistently with the increasing Reynolds number, and it is larger than the constant the-oretical value for macrochannels. The Reynolds number for the transition from laminar to turbu-lent flow is about 1500, which is lower than the value for macrochannels. For the heat transfer property, Nusselt number also increases with increasing Reynolds number, and larger roughness contributes to higher Nusselt number.     

Cutting tool temperature prediction method using analytical model for end milling

Dramatic tool temperature variation in end milling can cause excessive tool wear and shorten its life, especially in machining of difficult-to-machine materials. In this study, a new analyt-ical model-based method for the prediction of cutting tool temperature in end milling is presented. The cutting cycle is divided into temperature increase and decrease phases. For the temperature increase phase, a temperature prediction model considering real friction state between the chip and tool is proposed, and the heat flux and tool-chip contact length are then obtained through finite element simulation. In the temperature decrease phase, a temperature decrease model based on the one-dimension plate heat convection is proposed. A single wire thermocouple is employed to mea-sure the tool temperature in the conducted milling experiments. Both of the theoretical and experi-mental results are obtained with cutting conditions of the cutting speed ranging from 60 m/min to 100 m/min, feed per tooth from 0.12 mm/z to 0.20 mm/z, and the radial and axial depth of cut respec-tively being 4 mm and 0.5 mm. The comparison results show high agreement between the physical cutting experiments and the proposed cutting tool temperature prediction method.     

Experimental investigation on aero-heating of rudder shaft within laminar/turbulent hypersonic boundary layers

The aero-heating of the rudder shaft region of a hypersonic vehicle is very harsh, as the peak heat flux in this region can be even higher than that at the stagnation point. Therefore, studying the aero-heating of the rudder shaft is of great significance for designing the thermal protection system of the hypersonic vehicle. In the wind tunnel test of the aero-heating effect, we find that with the increase of the angle of attack of the lifting body model, the increasement of the heat flux of the rudder shaft is larger under laminar flow conditions than that under turbulent flow conditions. To understand this, we design a wind tunnel experiment to study the effect of laminar/turbulent hypersonic boundary layers on the heat flux of the rudder shaft under the same wind tunnel freestream conditions. The experiment is carried out in the ?2 m shock tunnel(FD-14 A) affiliated to the China Aerodynamics Research and Development Center(CARDC). The laminar boundary layer on the model is triggered to a turbulent one by using vortex generators, which are 2 mm-high diamonds. The aero-heating of the rudder shaft(with the rudder) and the protuberance(without the rudder) are studied in both hypersonic laminar and turbulent boundary layers under the same freestream condition. The nominal Mach numbers are 10 and 12, and the unit Reynolds numbers are2.4 × 10~6 m~(-1) and 2.1 × 10~6 m-1. The angle of attack of the model is 20°, and the deflection angle of the rudder and the protuberance is 10°. The heat flux on the model surface is measured by thin film heat flux sensors, and the heat flux distribution along the center line of the lifting body model suggests that forced transition is achieved in the upstream of the rudder. The test results of the rudder shaft and the protuberance show that the heat flux of the rudder shaft is lower in the turbulent flow than that in the laminar flow, but the heat flux of the protuberance is the other way around,i.e., lower in the laminar flow than in the turbulent flow. The wind tunnel test results is also validated by numerical simulations. Our analysis suggests that this phenomenon is due to the difference of boundary layer velocities caused by different thickness of boundary layer between laminar and turbulent flows, as well as the restricted flow within the rudder gap. When the turbulent boundary layer is more than three times thicker than that of the laminar boundary layer, the heat flux of the rudder shaft under the laminar flow condition is higher than that under the turbulent flow condition. Discovery of this phenomenon has great importance for guiding the design of the thermal protection system for the rudder shaft of hypersonic vehicles.     

Investigation of MHD power generation with supersonic non-equilibrium RF discharge

Magnetohydrodynamic (MHD) power generation with supersonic non-equilibrium plasma is demonstrated. Capacitively coupled radio frequency (RF) discharge (6 MHz, maximum continual power output of 200 W) was adopted to ionize the Mach number 3.5 (650 m/s), 0.023 kg/m3 airflow. In a MHD channel of 16 mm × 10 mm × 20 mm, MHD open voltage of 10 V is realized in the magnetic field of 1.25 T, and power of 0.12 mW is extracted steadily and con-tinuously in the magnetic field of 1 T. The reasons for limited power generation are proposed as:low conductivity of RF discharge; large touch resistance between MHD electrode and plasma;strong current eddies due to flow boundary layer. In addition, the cathode voltage fall is too low to have obvious effects on MHD power generation.     

An experimental system for release simulation of internal stores in a supersonic wind tunnel

Aerodynamic parameters obtained from separation experiments of internal stores in a wind tunnel are significant in aircraft designs. Accurate wind tunnel tests can help to improve the release stability of the stores and in-flight safety of the aircrafts in supersonic environments.A simulative system for free drop experiments of internal stores based on a practical project is provided in this paper. The system contains a store release mechanism, a control system and an attitude measurement system. The release mechanism adopts a six-bar linkage driven by a cylinder, which ensures the release stability. The structure and initial aerodynamic parameters of the stores are also designed and adjusted. A high speed vision measurement system for high speed rolling targets is utilized to measure the pose parameters of the internal store models and an optimizing method for the coordinates of markers is presented based on a priori model. The experimental results show excellent repeatability of the system, and indicate that the position measurement precision is less than0.13 mm, and the attitude measurement precision for pitch and yaw angles is less than 0.126°, satisfying the requirements of practical wind tunnel tests. A separation experiment for the internal stores is also conducted in the FL-3 wind tunnel of China Aerodynamics Research Institute.     

An adaptive attitude algorithm based on a current statistical model for maneuvering acceleration

A current statistical model for maneuvering acceleration using an adaptive extended Kalman filter(CS-MAEKF) algorithm is proposed to solve problems existing in conventional extended Kalman filters such as large estimation error and divergent tendencies in the presence of continuous maneuvering acceleration. A membership function is introduced in this algorithm to adaptively modify the upper and lower limits of loitering vehicles' maneuvering acceleration and for realtime adjustment of maneuvering acceleration variance. This allows the algorithm to have superior static and dynamic performance for loitering vehicles undergoing different maneuvers. Digital simulations and dynamic flight testing show that the yaw angle accuracy of the algorithm is 30% better than conventional algorithms, and pitch and roll angle calculation precision is improved by 60%.The mean square deviation of heading and attitude angle error during dynamic flight is less than3.05°. Experimental results show that CS-MAEKF meets the application requirements of miniature loitering vehicles.     

Modeling and simulation of a time-varying inertia aircraft in aerial refueling

Studied in this paper is dynamic modeling and simulation application of the receiver aircraft with the time-varying mass and inertia property in an integrated simulation environment which includes two other significant factors, i.e., a hose–drogue assembly dynamic model with the variable-length property and the wind effect due to the tanker's trailing vortices. By extending equations of motion of a fixed weight aircraft derived by Lewis et al., a new set of equations of motion for a receiver in aerial refueling is derived. The equations include the time-varying mass and inertia property due to fuel transfer and the fuel consumption by engines, and the fuel tanks have a rectangle shape rather than a mass point. They are derived in terms of the translational and rotational position and velocity of the receiver with respect to an inertial reference frame. A linear quadratic regulator(LQR) controller is designed based on a group of linearized equations under the initial receiver mass condition. The equations of motion of the receiver with a LQR controller are implemented in the integrated simulation environment for autonomous approaching and station-keeping of the receiver in simulations.     

Variational Bayesian labeled multi-Bernoulli filter with unknown sensor noise statistics

It is difficult to build accurate model for measurement noise covariance in complex back-grounds. For the scenarios of unknown sensor noise variances, an adaptive multi-target tracking algorithm based on labeled random finite set and variational Bayesian (VB) approximation is pro-posed. The variational approximation technique is introduced to the labeled multi-Bernoulli (LMB) filter to jointly estimate the states of targets and sensor noise variances. Simulation results show that the proposed method can give unbiased estimation of cardinality and has better performance than the VB probability hypothesis density (VB-PHD) filter and the VB cardinality balanced multi-target multi-Bernoulli (VB-CBMeMBer) filter in harsh situations. The simulations also confirm the robustness of the proposed method against the time-varying noise variances. The computational complexity of proposed method is higher than the VB-PHD and VB-CBMeMBer in extreme cases, while the mean execution times of the three methods are close when targets are well separated.     

Constraining Fundamental Constants of Physics with Quasar Absorption Line Systems

We summarize the attempts by our group and others to derive constraints on variations of fundamental constants over cosmic time using quasar absorption lines. Most upper limits reside in the range 0.5–1.5×10^?5 at the 3σ level over a redshift range of approximately 0.5–2.5 for the fine-structure constant, α, the proton-to-electron mass ratio, μ and a combination of the proton gyromagnetic factor and the two previous constants, g _p(α ²/μ) ^ν , for only one claimed variation of α. It is therefore very important to perform new measurements to improve the sensitivity of the numerous methods to at least <0.1×10^?5 which should be possible in the next few years. Future instrumentations on ELTs in the optical and/or ALMA, EVLA and SKA pathfinders in the radio will undoutedly boost this field by allowing to reach much better signal-to-noise ratios at higher spectral resolution and to perform measurements on molecules in the ISM of high redshift galaxies.     

Fretting wear behaviour of machined layer of nickel-based superalloy produced by creep-feed profile grinding

Fretting wear has an adverse impact on the fatigue life of turbine blade roots. The current work is to comparatively investigate the fretting wear behaviour of the nickel-based superalloy surfaces produced by polishing and creep-feed profile grinding, respectively, in terms of surface/subsurface fretting damage, the friction coefficient, wear volume and wear rate. Experimental results show that the granulated tribolayer aggravates the workpiece wear, while the flat compacted tribolayer enhances ...     

Direct thrust test and asymmetric performance of porous ionic liquid electrospray thruster

In order to meet the demand of CubeSats for low power and high-performance micro-propulsion system, a porous ionic liquid electrospray thruster prototype is developed in this study. 10 × 10 conical emitter arrays are fabricated on an area of 3.24 cm² by computer numerical control machining technology. The propellant is 1-ethyl-3-methylimidazolium tetrafluoroborate. The overall dimension of the assembled prototype is 3 cm × 3 cm × 1 cm, with a total weight of about 15 g (with propellant). The performance of this prototype is tested under vacuum. The results show that it can work in the voltage range of ±2.0 kV to ±3.0 kV, and the maximum emission current and input power are about 355 μA and 1.12 W. Time of Flight (TOF) mass spectrometry results show that cationic monomers and dimers dominate the beam in positive mode, while a higher proportion of higher-order solvated ion clusters in negative mode. The maximum specific impulse is 2992 s in positive mode and 849 s in negative mode. The thrust is measured in two methods: one is calculated by TOF results and the other is directly measured by high-precision torsional thrust stand. The thrust (T) obtained by these two methods conforms to a certain scaling law with respect to the emission current (I_em) and the applied voltage (V_app), following the scale of T ∼ I_emV_app^0.5, and the thrust range is from 2.1 μN to 42.6 μN. Many thruster performance parameters are significantly different in positive and negative modes. We speculate that due to the higher solvation energy of the anion, more solvated ion clusters are formed rather than pure ions under the same electric field. It may help to improve thruster performance if porous materials with smaller pore sizes are used as reservoirs. Although there are still many problems, most of the performance parameters of ILET-3 are good, which can theoretically meet the requirements of CubeSats for micro-propulsion system.     

Composition of Interstellar Neutrals and the Origin of Anomalous Cosmic Rays

Knowledge of the elemental composition of the interstellar gas is of fundamental importance for understanding galactic chemical evolution. In addition to spectroscopic determinations of certain element abundance ratios, measurements of the composition of interstellar pickup ions and Anomalous Cosmic Rays (ACRs) have provided the principal means to obtain this critical information. Recent advances in our understanding of particle acceleration processes in the heliosphere and measurements by the Voyagers of the energy spectra and composition of energetic particles in the heliosheath provide us with another means of determining the abundance of the neutral components of the local interstellar gas. Here we compare the composition at the termination shock of six elements obtained from measurements of (a) pickup ions at ～5 AU, (b) ACRs in the heliosphere at ～70 AU, and (c) energetic particles as well as (d) ACRs in the heliosheath at ～100 AU. We find consistency among these four sets of derived neutral abundances. The average interstellar neutral densities at the termination shock for H, N, O, Ne and Ar are found to be 0.055±0.021 cm^?3, (1.44±0.45)×10^?5 cm^?3, (6.46±1.89)×10^?5 cm^?3, (8.5±3.3)×10^?6 cm^?3, and (1.08±0.49)×10^?7 cm^?3, respectively, assuming the He density is 0.0148±0.002 cm^?3.     

Atom-Based Test of the Equivalence Principle

We describe a test of the equivalence principle with quantum probe particles based on atom interferometry. For the measurement, a light pulse atom interferometer based on the diffraction of atoms from effective absorption gratings of light has been developed. A differential measurement of the Earth’s gravitational acceleration g for the two rubidium isotopes ⁸⁵Rb and ⁸⁷Rb has been performed, yielding a difference Δg/g=(1.2±1.7)×10^?7. In addition, the dependence of the free fall on the relative orientation of the electron to the nuclear spin was studied by using atoms in two different hyperfine states. The determined difference in the gravitational acceleration is Δg/g=(0.4±1.2)×10^?7. Within their experimental accuracy, both measurements are consistent with a free atomic fall that is independent from internal composition and spin orientation.     

Grad-Shafranov Reconstruction of Magnetic Flux Ropes in the Near-Earth Space

Electric currents permeate space plasmas and often have a significant component along the magnetic field to form magnetic flux ropes. A larger spatial perspective of these structures than from the direct observation along the satellite path is crucial in visualizing their role in plasma dynamics. For magnetic flux ropes that are approximately two-dimensional equilibrium structures on a certain plane, Grad-Shafranov reconstruction technique, developed by Bengt Sonnerup and his colleagues (see Sonnerup et al. in J. Geophys. Res. 111:A09204, 2006), can be used to reveal two-dimensional maps of associated plasma and field parameters. This review gives a brief account of the technique and its application to magnetic flux ropes near the Earth’s magnetopause, in the solar wind, and in the magnetotail. From this brief survey, the ranges of the total field-aligned current and the total magnetic flux content for these magnetic flux ropes are assessed. The total field-aligned current is found to range from ∼0.14 to ∼9.7×10⁴ MA, a range of nearly six orders of magnitude. The total magnetic flux content is found to range from ∼0.25 to ∼2.3×10⁶ MWb, a range of nearly seven orders of magnitude. To the best of our knowledge, this review reports the largest range of both the total field-aligned current and the total magnetic flux content for magnetic flux ropes in space plasmas.     

A visco-elastoplastic constitutive model of aircraft polymethylmethacrylate related to strain rate and temperature

The visco-elastoplastic mechanical behavior related to the applied strain rate and temperature around the glass transition temperature of Polymethylmethacrylate (PMMA) has been systematically investigated. The uniaxial tensile test was performed at strain rate and temperature rangs 1.0 × 10⁻⁴–1.0 × 10⁻² s⁻¹ and 363–393 K, respectively, and the Dynamic Mechanical Analysis (DMA) test was carried out between 363 K and 413 K at various frequencies. Moreover, the robust complex constitutive model considering the temperature and strain rate effect is proposed. A nonlinear viscoelastic model is established to describe the viscoelastic response on the basis of the Zhu-Wang-Tang (ZWT) model and the time temperature equivalence principle, including the dependence of strain rate and temperature. Considering the yield stress, the cooperative model is adopted. The viscoplastic mechanical response is manifested as the competition performance of the softening deformation and hardening behavior. The predicted mechanical responses maintain good consistency with the experimental results, indicating that the visco-elastoplastic constitutive model proposed can accurately predict the mechanical behavior of PMMA materials within the imposed strain rate and near the glass transition temperature range.     

Frequency steering of spaceborne clocks based on XPNAV-1 observations

Due to high stable rotations, timing of pulsars provides a natural tool to correct the frequency deviation of spaceborne atomic clocks. Based on processing the observational data about a year of Crab pulsar given by XPNAV-1 satellite, we study the possibility of correcting the frequency deviation of spaceborne atomic clocks using pulsar timing. According to the observational data in X-ray band and the timing model parameters from radio observations, the pre-fit timing residuals with a level of 6...     

Frictional resistance of supercritical pressure RP-3 flowing in a vertically downward tube at constant heat fluxes

Based on the demands of compact heat exchangers and micro cooling channels applied for aviation thermal protection, the flow resistance characteristics of aviation kerosene RP-3 were experimentally studied in a vertically downward circular miniature tube with an inner diameter of 1.86 mm at supercritical pressures and constant heat fluxes. A long and short tube method was used to accurately calculate the frictional pressure drop, and experimental conditions are supercritical pressures of 4 MPa, mass flow rates of 2–4 g/s (i.e., mass fluxes of 736–1472 kg/(m²?s)), heat fluxes of 100–500 kW/m², and inlet temperatures of 373–673 K. Results show that the sharp variations of thermophysical properties, especially density, have significant influences on frictional resistances. Generally, the frictional pressure drop and the friction factor increase with increasing inlet temperatures, and this trend speeds up in the relatively high-temperature region. However, the friction factor has a sudden decline when the fuel outlet temperature exceeds the pseudo-critical temperature. The frictional pressure drop and the friction factor basically remain unchanged with increasing heat flux when the inlet temperature is relatively low, but increase quickly when the inlet temperature is relatively high. Besides, a larger mass flux yields a higher pressure drop but does not necessarily yield a higher friction factor. Finally, an empirical friction factor correlation is proposed and shows better predictive performance than those of previous models.