Development of three-dimensional numerical model for combustion-flow in interior ballistics

Interior ballistics analysis is required for the development of the gun system. Interior ballistics is a complex phenomenon containing the propellant combustion and gas flow and is completed in tens of milliseconds during gun firing. Thus, some data cannot be directly measured by experiment. Numerical analysis is therefore traditionally used to understand the complex gun firing phenomena. In previous studies, the two-dimensional axisymmetric numerical method for interior ballistics using the Eulerian-Lagrangian approach has been developed. There are some limits in depicting the actual phenomena with two-dimensional models. Therefore, a three-dimensional numerical model has been built in the present study. Unlike the conventional method, the calculation has been conducted by separating the physical phenomena into the combustion part and the flow part for simplicity and efficiency. The internal flow in the gun barrel has been calculated by using the STAR-CCM+ and the source terms produced by the propellant combustion has been computed by utilizing the existing code. The developed numerical model has been compared with the AGARD gun results and the simulation of 40 mm gun firings. The reliability of the developed model has been confirmed because the results of the numerical analysis greatly agree with the simulation results. The basis of the three-dimensional analysis of the interior ballistics has been formed through this study.     

Numerical study of gas-solid reactive flow in a cylinder

A theoretical model is described for the numerical simulation of unsteady gas-solid reactive flow in packed beds of granular propellants in a tubular geometry. The approach couples continuity, momentum and energy equations in each phase along with porosity and granular stresses. Propellant bed combustion process is neglected, but the mass flow rate due to the combustion is derived using a pressure-based burning rate correlation. As the burning of solid propellant begins, pressure, temperature, density and other gas parameters begin to change rapidly. To catch these changes, a CFD approach with explicit McCormack method is used to solve the coupled system of equations. A moving mesh is used to consider the moving boundary. Pressure history, moving boundary velocity and other parameters of the mixture are obtained and compared with other numerical data.     

Flow instability due to cryogenic cavitation in the downstream of orifice

Flow instability in LRE (liquid rocket engine) occurs due to various reasons such as flow interactions with valve, orifice and venturi, etc. The inception of cavitation, especially in the propellant feeding system, is the primary cause of mass and pressure oscillations because of the cyclic formation and depletion of cavitation. Meanwhile, the main propellant in a liquid rocket engine is the cryogenic fluid, which properties are very sensitive to temperature variation. And the change of propellant properties to temperature variation by thermodynamic effect needs to be properly taken into account in the flow analysis in order to understand basic mechanisms for cryogenic cavitation. The present study focuses on the formation of cryogenic cavitation by using the IDM model suggested by Shyy and coworkers. The flow instability was also numerically investigated in the downstream of orifice with a developed numerical code. Calculation results show that cryogenic cavitation can be a primary source of flow instability, leading to mass fluctuations accompanied by pressure oscillations. The prediction of cavitation in cryogenic fluid is of vital importance in designing a feeding system of an LRE. This paper was recommended for publication in revised form by Associate Editor Jun Sang Park Changjin Lee received his B.S. and M.S. degrees in Aeronautical Engineering from Seoul National University in 1983 and 1985. He then went on to receive his Ph.D. degree from University of Illinois at Urbana- Champaign in 1992. Dr. Lee is currently a Professor at the department of Aerospace Engineering at Konkuk University in SEOUL, Korea. His research interests are in the area of combustion instabilities of hybrid, liquid rocket and jet propulsions. Tae-Seong Roh received his B.S. and M.S. degrees in Aeronautical Engineering from Seoul National University in 1984 and 1986. He then went on to receive his Ph.D. degree from Pennsylvania State University in 1995. Dr. Roh is currently a Professor at the department of Aerospace Engineering at Inha University in Incheon, Korea. His research interests are in the area of combustion instabilities, rocket and jet propulsions, interior ballistics, and gas turbine engine defect diagnostics.     

大变形成形过程刚塑性无网格伽辽金方法

在非稳态大变形塑性成形过程中，由于节点的大范围移动和流动的非均匀性，导致分析精度下降。针对移动最小二乘近似精度的提高，尤其是边界附近节点分析近似精度的提高，提出了相应的处理方案，以保证分析的精度。通过采用影响域节点控制方法以及边界节点分布密度动态控制方法，实现了塑性成形过程的无网格伽辽金方法的自适应分析。对拉普拉斯方程及典型的大变形成形过程进行了分析，通过与拉普拉斯方程解析解和相应的商品化刚塑性有限元软件Deform的分析结果进行对比，验证了处理方案的正确性。     

Investigation of liquid-gas interfacial shapes in reduced gravitational environments

The objective of this study was to investigate the liquid-gas interfacial shapes in a low-gravity environment. Experimentally, a free-falling test setup was established to perform drop tests for observing interfacial flow phenomena under reduced-gravity conditions. In the theoretical analysis, the complex two-phase flowfield was simulated by using the transient three-dimensional conservation equations of mass and momentum. The continuous surface force (CSF) model was adopted to treat the surface-tension effect at the liquid-gas boundary. The volume-of-fluid (VOF) method, together with the piecewise linear interface construction (PLIC) technique, was used to describe the liquid-gas interface movements. The predictions were compared with the photographed images of the water-air interface shapes to validate the present computer code. To extend the application to the internal flow study of a ROCSAT-2 propellant tank, 16 numerical experiments were conducted to examine various effects, including liquid-filled ratio, gravity level, surface tension, and contact angle on the equilibrium shape of the pressurized helium gas bubble and the location of the center of mass (CoM).     

Parallel computation of two-phase flow in a microchannel using the lattice Boltzmann method

We present a numerical simulation of two-phase flow in a three-dimensional cross-junction microchannel by using the lattice Boltzmann method (LBM). At first, we validated our LBM code with the velocity profile in a 3-dimensional rectangular channel. Then, we developed a lattice Boltzmann code based on the free energy model to simulate the immiscible binary fluid flow. The parallelization of the developed code is implemented on a PC cluster using the MPI program. The numerical results of two-phase flow in the microchannel reveal droplet formation process, which compares well with corresponding experimental results. The size of droplet decreases with increase of the flow-rate ratio and the capillary number. The movement of a droplet through the microchannel induces three-dimensional circulating flow inside the droplet. This complex flow is thought to enhance the mixing and reaction of reagents.     

A two-stage pellet injector with a cryogenic piston for plasma fueling of thermonuclear devices

A new two-stage gun was developed for solid-hydrogen-or deuterium-pellet formation and injection into plasma of thermonuclear devices. A cryogenic piston made from solid carbon dioxide was first used to compress and heat the propellant gas in the second gun stage. The piston was produced simultaneously with fuel pellets before each shot. Deuterium pellets with a 1.5-mm diameter and up to 5-mm length were accelerated to a speed of 1.7 km/s. The experimental results of cryogenic-piston formation with a 4-mm diameter and up to 30-mm length are presented.     

驾驶室结构振动及其声固耦合噪声响应分析

利用有限元分析软件ANSYS和声学分析软件SYSNO ISE对卡车驾驶室的振动与内部声场耦合做了数值计算分析研究。介绍了振动频响分析方法,动力学计算与声学边界元模型耦合的具体步骤。通过计算分析,分别研究了驾驶室结构的声固耦合模型与非耦合模型对室内声场的影响,从而找出在不同的壁板厚度条件下,声固耦合作用对室内噪声的影响,以及驾驶室内声场的变化规律。     

Experimental study and finite element analysis of simple X- and T-branch tube hydroforming processes

The tube hydroforming process is a relatively complex manufacturing process; the performance of this process depends on various factors and requires proper combination of part design, material selection and boundary conditions. Due to the complex nature of the process, the best method to study the behaviour of the process is by using numerical techniques and advanced explicit finite element (FE) codes. In this work, X- and T-branch components were formed using a tube hydroforming machine and experimental load paths (forming pressure and axial feed) were obtained for the processes via a data acquisition system integrated with the machine. Subsequently, the processes were simulated using LS-DYNA3D explicit FE code using the same experimental boundary, loading conditions and the simulation results were compared with the experimental results. It was found that the developed branch height and the wall thickness distribution along different planes were in good agreement with the experimental results.     

Numerical simulation of the unsteady combustion of solid rocket propellants at a harmonic pressure change

This study focuses on a numerical investigation of the unsteady burning rate of solid propellants at a harmonic pressure change in the combustion chamber of a solid propellant rocket engine. The physico-mathematical model includes the equations of heat transfer and decomposition of the oxidizer in the solid phase and two phases, the dual velocity, and the two-temperature reaction flow of gasification products. The boundary conditions on the solid fuel surface implement the conservation of energy fluxes and the mass of components. We numerically calculate the unsteady burning rate of metallized solid propellant and nitroglycerin powder under a harmonic pressure change in the combustion chamber of a solid propellant rocket engine and determine the dependence of the burning rate amplitude on the frequency of pressure oscillations. The amplitude of the burning rate depends nonmonotonously on the oscillation frequency. With increasing frequency, the amplitude first rises and then declines.

     

Simulation of sloshing in a bi-lobe tank under arbitrary rotation using the FDS scheme and the HCIB method

Three-dimensional sloshing in a bi-lobe tank under arbitrary rotation is simulated using a code developed using the flux-difference splitting scheme for variable density incompressible fluids and the hybrid Cartesian/immersed boundary method. The material interface is regarded as a moving contact discontinuity and is captured using a free surface capturing method derived from the Riemann solver, without any additional treatment along the interface. The boundary condition for the arbitrary motion of the bi-lobe tank, which contains a thin partition between two partially overlapping cylindrical tanks, is handled with ease by using the hybrid Cartesian/immersed boundary method. The computed time evolution of the interface is compared with the snapshots taken during the experiments on sloshing caused by the sway motion of the bi-lobe tank. Good agreement is observed between the computational and experimental results. The validated code is used to simulate three-dimensional sloshing in the bi-lobe tank that is subject to combined pitch and roll motions. A rotational vector is used to locate the Lagrangian points of the unstructured surface grid according to the motion of the tank. Grid independence tests are carried out using three different size grids. Violent three-dimensional sloshing ensues with an increase in the angular velocity of rotation.     

Finite element analysis of fluid flows with moving boundary

The objective of the present study is to analyze the fluid flow with moving boundary using a finite element method. The algorithm uses a fractional step approach that can be used to solve low-speed flow with large density changes due to intense temperature gradients. The explicit Lax-Wendroff scheme is applied to nonlinear convective terms in the momentum equations to prevent checkerboard pressure oscillations. The ALE (Arbitrary Lagrangian Eulerian) method is adopted for moving grids. The numerical algorithm in the present study is validated for two-dimensional unsteady flow in a driven cavity and a natural convection problem. To extend the present numerical method to engine simulations, a piston-driven intake flow with moving boundary is also simulated. The density, temperature and axial velocity profiles are calculated for the three-dimensional unsteady piston-driven intake flow with density changes due to high inlet fluid temperatures using the present algorithm. The calculated results are in good agreement with other numerical and experimental ones.     

Moving mesh application for thermal-hydraulic analysis in cable-in-conduit-conductors of KSTAR superconducting magnet

In order to study the thermal-hydraulic behavior of the cable-in-conduit-conductor (CICC), a numerical model has been developed. In the model, the high heat transfer approximation between superconducting strands and supercritical helium is adopted. The strong coupling of heat transfer at the front of normal zone generates a contact discontinuity in temperature and density. In order to obtain the converged numerical solutions, a moving mesh method is used to capture the contact discontinuity in the short front region of the normal zone. The coupled equation is solved using the finite element method with the artificial viscosity term. Details of the numerical implementation are discussed and the validation of the code is performed for comparison of the results with thse of GANDALF and QSAIT.     

考虑动力学因素的喷漆机器人喷枪路径优化

机器人在喷漆作业过程中大部分时间是在做路径相似的重复空间轨迹运动,对于一个特定的作业对象,喷枪的运动路径可能有不同的形式。本文针对平面工件表面的喷漆作业,建立了喷枪喷矩模型,然后基于漆膜厚度变化的方差最小,用遗传算法对喷枪运动路径的参数进行优化,由于运枪方向不同而得到两种路径方案,再从机器人的动力学角度出发,以使整个路径中最大关节力矩和最小为目标,对喷枪路径进行优选,以达到既保证喷漆质量又能使机器人关节驱动电机的负载最小的目的。     

非线性方程组解集边界求解方法及其在并联机构分析中的应用

并联机构的结构使其输入和输出运动之间具有复杂的非线性关系,在该类机构的运动学、动力学、作业空间、误差分析及运动控制中均涉及大量的非线性方程组求解。介绍一种含参数的非线性方程组的解集边界求解方法,基于流形理论和数值化连续算法,可直接搜索出一个非线性系统的解集边界,计算速度快、效率高。利用上述算法,对一台实际的4自由度并联机床进行了作业空间边界的求解和分析,验证了算法的实用性和有效性。     

基于仿真的某型火炮极限射击条件研究

火炮极限射击条件用于考核火炮在最严酷射击条件下的工作情况,传统火炮极限射击条件是在对影响参量定性分析基础上,依据经验大致确定的。为准确确定某火炮的极限射击条件,将内弹道模型和火炮反后坐装置模型结合起来,建立了系统的火炮射击数值仿真模型,在仿真的基础上,首先分析了相关参量对射击条件的影响;而后用人工神经网络拟合仿真计算以减少仿真时间、用模拟退火和基因算法等优化算法对射击条件进行优化,得到了极限射击条件;最后,计算了极限射击条件位置各影响参量的灵敏度。     

Thermal analysis of dry sleeve bearings — a comparison between analytical, numerical (finite element) and experimental results

Thermal analysis of a plastic sleeve bearing in dry operation was investigated experimentally by Floquet et al. [Trans. ASME, J. Lubr. Technol. 99 (1977) 277]. For a comparison with the experimental results, Kennedy [Trans. ASME, J. Tribol. 103 (1981) 90] developed a numerical approach using the finite element method (FEM) that included the development of finite element equations for the case of a moving body heat conduction. In this investigation, both the experimental results of Floquet [Docteur-Ingenier thesis, Université Claude Bernard, Lyon, 1978] and the numerical results of Kennedy were compared with the results of the analytical method developed using the classical heat source method introduced by Jaeger [Proc. Roy. Soc. NSW 76 (1942) 203] and the heat partition principles of Blok [Proc. Inst. Mech. Engrs. 2 (1937) 222], which involves matching of the temperatures on either side of the contact interface. The non-uniform distribution of heat partition (as one body is stationary and the other moving) along the interface is addressed by matching the temperatures at the interface between the stationary and the moving bodies in relative sliding contact using the functional analysis approach originally introduced by Chao and Trigger [Trans. ASME 72 (1955) 1107]. The analytical results are found to be in excellent agreement with both the experimental and the numerical results.     

含ACP的无烟改性双基推进剂燃烧特性研究

快燃物ACP作为一种有效含能助剂用来提高推进剂的燃速具有一定的效果。通过DSC和TG-DTG研究了ACP对无烟改性双基推进剂(CMDB)热分解特性的影响,采用靶线法研究了不同含量的ACP对无烟改性双基推进剂燃速和燃速压力指数的影响,用燃烧火焰单幅照相技术和微热电偶测温获得了含ACP无烟改性双基推进剂在稳态燃烧条件下的火焰结构和燃烧波温度分布,分析了该推进剂中主要组分对燃烧性能的影响。结果表明:含ACP推进剂的燃速随ACP含量的增加而增大,推进剂燃烧火焰结构随ACP含量增加而更加明亮。     

CFD-DEM simulation on the complex gas-solid flow in a closed chamber with particle groups

There is a complex gas-solid flow in the cylindrical closed chamber during the interior ballistic process in a modular-charge gun launch. The motion and the distribution of particles in the flow have significant effects on the combustion stability in the interior ballistic process. Therefore, the solid particle-scale details of the gas-solid flow in the closed chamber with hollow-cylindrical particle groups were numerically simulated by using the computational fluid dynamics combined with the discrete element method (CFD-DEM). The results show that the particle final distribution is composed of a gentle-slope accumulation, a horizontal accumulation, and a steep-slope accumulation. Thereinto, the voidage of the steep-slope accumulation is decreased with the axial position far away from modules. With the increase of the initial spacing between two particle groups, the axial length of the steep-slope accumulation is increased exponentially, whereas the tangent value of the inclined angle is decreased exponentially.