Numerical Analysis on Thermal Function of Clothing with PCM Microcapsules

To study the influences of phase change material(PCM)microcapsules in clothing on human thermal responses,a mathematical model is developed.The improved Stolwijk’s model is used to simulate human thermo-regulatory process,and the coupled heat and moisture transfer including the moisture sorption/desorption of fibers and effects of phase transition temperature range on the phase change processes of the PCM is considered in clothing model.Meanwhile,the theoretical predictions are validated by experimental data.Then,the interactions between human body thermal responses and the heat and moisture transfer in clothing are discussed by comparing the prediction results with PCMs and without PCMs.Also the effects of fiber hygroscopicity on clothing and human thermal responses are compared.The conclusion shows that the clothing with PCMs microcapsules can delay the human temperature variations and decrease the sweat accumulation rate on the skin surface and heat loss during changing of ambient conditions,and fiber hygroscopicity reduces the effect of PCM microcapsules on delaying garment temperature variations very significantly.

Refined modeling and experimental verification of a torque motor for an electro-hydraulic servo valve

The Permanent Magnet Torque Motor(PMTM)is the key electro-mechanical conversion device in an Electro-Hydraulic Servo Valve(EHSV).In this work,a refined model of a PMTM is developed,considering the non-working air-gaps between the upper or lower yoke and the armature,the fringing effect at the limiting holes,and the nonlinear permeability of soft magnetic material.Based on the refined model,the influences of various factors on the calculation accuracy of the magnetic flux at the pole surfaces of the armature and the output torque are investigated.For verifying the validity of the refined model,a Finite Element Analysis(FEA)of the PMTM is conducted,and a test platform is constructed.Compared with existing models,the refined model can better reveal the intrinsic mechanism of the PMTM,and its calculations are more consistent with the FEA results.The experimental results of the armature deflection displacement show that the refined model can accurately describe the output characteristics of the PMTM.

Experimental comparison between aircraft fuel tank inerting processes using NEA and MIG

Fuel tank inerting technologies are able to reduce the fire risk by injection of inert gas into the ullage or fuel, the former called ullage washing and the latter fuel scrubbing. The Green On-Board Inert Gas Generation System（GOBIGGS） is a novel technology based on flameless catalytic combustion, and owning to its simple structure and high inerting efficiency, it has received a lot of attentions. The inert gas in the GOBIGGS is mainly comprised of CO2, N2, and O2（hereinafter, Mixed Inert Gas（MIG））, while that in the On-Board Inert Gas Generation System（OBIGGS）, which is one of the most widely used fuel tank inerting technologies, is NitrogenEnriched Air（NEA）. The solubility of CO2 is nearly 20 times higher than that of N2 in jet fuels,so the inerting capability and performance are definitely disparate if the inert gas is selected as NEA or MIG. An inerting test bench was constructed to compare the inerting capabilities between NEA and MIG. Experimental results reveal that, if ullage washing is adopted, the variations of oxygen concentrations on the ullage and in the fuel are nearly identical no matter the inert gas is NEA or MIG. However, the ullage and dissolved oxygen concentrations of MIG scrubbing are always higher than those of NEA scrubbing.

Simulation and experimental investigation of inner-jet electrochemical grinding of GH4169 alloy

GH4169 alloy is one of the most commonly used materials in aero engine turbine blades,but its machinability is poor because of its excellent strength at high temperatures. Electrochemical machining（ECM） has become a common method for machining this alloy and other difficult-tomachine materials. Electrochemical grinding（ECG） is a hybrid process combining ECM and conventional grinding. In this paper, investigations conducted on inner-jet ECG of GH4169 alloy are described. Two types of inner-jet ECG grinding wheels were used to machine a flat bottom surface.The machining process was simulated using COMSOL software, and machining gaps under different machining parameters were obtained. In addition, maximum feed rates and maximum material removal rates under different machining parameters were studied experimentally. The maximum sizes and the uniformity of the distributions of the gaps machined by the two grinding wheels were compared. The effects of different applied voltages on the machining results were also investigated.

Numerical simulation of a cabin ventilation subsystem in a space station oriented real-time system

An environment control and life support system（ECLSS） is an important system in a space station. The ECLSS is a typical complex system, and the real-time simulation technology can help to accelerate its research process by using distributed hardware in a loop simulation system. An implicit fixed time step numerical integration method is recommended for a real-time simulation system with time-varying parameters. However, its computational efficiency is too low to satisfy the real-time data interaction, especially for the complex ECLSS system running on a PC cluster. The instability problem of an explicit method strongly limits its application in the ECLSS real-time simulation although it has a high computational efficiency. This paper proposes an improved numerical simulation method to overcome the instability problem based on the explicit Euler method. A temperature and humidity control subsystem（THCS） is firstly established, and its numerical stability is analyzed by using the eigenvalue estimation theory. Furthermore, an adaptive operator is proposed to avoid the potential instability problem. The stability and accuracy of the proposed method are investigated carefully. Simulation results show that this proposed method can provide a good way for some complex time-variant systems to run their real-time simulation on a PC cluster.

Reflected shock/turbulent boundary layer interaction structure analysis based on large eddy simulation

In order to understand the physical phenomenon of the reflected shock/turbulent boundary layer interaction,the Large Eddy Simulation(LES)is conducted to investigate shock wave and turbulent boundary layer interaction in a 12°compression ramp with inlet high Mach number of 2.9.Rescaling/recycling method is used as inflow turbulence generation technique and validated on a supersonic flat plate turbulent boundary layer.The flow field of recycling plane in the plate computation domain is obtained to give the inlet boundary condition for the LES computation.This paper focuses on the reflected shock/turbulent boundary layer interaction region,where the fine flow structure and instantaneous flow field are analyzed in detail.It is found that the unsteady motion of the shock wave leads to the increase of wall pressure fluctuation.