Modeling phase change problems numerically is vital for understanding many natural (e.g., ice formation, steam generation) and engineering processes (e.g., casting, welding, additive manufacturing). Almost all phase change materials (PCMs) exhibit density/volume changes during melting, solidification, boiling, or condensation, causing additional fluid flow during this transition. Most numerical works consider only two phase flows (either solid-liquid or liquid-gas) for modeling phase change phenomena and some also neglect volume/density change of PCMs in the models. This paper presents a novel low Mach enthalpy method for simulating solidification and melting problems with variable thermophysical properties, including density. Additionally, this formulation allows coupling a solid-liquid PCM with a gas phase in order to simulate the free surface dynamics of PCMs undergoing melting and solidification. We revisit the two-phase Stefan problem involving a density jump between two material phases. We propose a possible means to include the kinetic energy jump in the Stefan condition while still allowing for an analytical solution. The new low Mach enthalpy method is validated against analytical solutions for a PCM undergoing a large density change during its phase transition. Additionally, a few simple sanity checks are proposed to benchmark computational fluid dynamics (CFD) algorithms that aim to capture the volume change effects of PCMs.
Diffuse-interface modeling and simulation of the freezing of binary fluids with the Marangoni effect
School of Mathematics and Statistics, Huazhong University of Science and Technology（华中科技大学数学与统计学院）；Hubei Key Laboratory of Engineering Modeling and Scientific Computing, Huazhong University of Science and Technology（华中科技大学工程建模与科学计算湖北省重点实验室）；The State Key Laboratory of Intelligent Manufacturing Equipment and Technology, Huazhong University of Science and Technology（华中科技大学智能装备制造与技术国家重点实验室）
Global modal/non-modal analysis of high-enthalpy Martian entry vehicles
Graduate Aerospace Laboratories, California Institute of Technology（加州理工学院高等航空实验室）；Department of Aeronautics and Astronautics, Massachusetts Institute of Technology（麻省理工学院航空航天系）
Effect of non-parallel mean flow on the acoustic spectrum of heated supersonic jets: explanation of `jet quietening'
在超声速马赫数一定的条件下，轴对称热射流的噪声测量表明，随着温度比的增加，声频谱减小。使用大涡模拟（LES）在实验和计算上都观察到了“光谱静噪”效应。Afsar { \it et al}对此进行了解释。（M. Z. Afsar和M. E. Goldstein $\&$ A. M. Fagan AIAAJ.，Vol.49，p.2522，2011）通过使用广义声学类比公式的焓通量/动量通量耦合项引入的抵消。但是平行流假设在高喷流速度下给出的预测是不准确的。因此，本文推广了Goldstein { \it et al}的非平行流渐近理论。（M. E.戈尔茨坦，A. Sescu $\&$ M. Z. Afsar，J. Fluid Mech.，Vol.695，p.199，2012）用于类比中的伴随线性化欧拉方程（ALEE）的向量格林函数。采用定常雷诺平均Navier Stokes（RANS）方法计算射流平均流场，当考虑非平行流效应和湍流结构的自洽近似时，耦合项传播子在对应于峰值射流噪声的低频处是正定的且渐近次主导的。通过计算整体声压级（OASPL），在不同的观测角度下对基于非平行流的声学模拟模型的有效性进行了评估，并以此对消声效果提出了更合理的解释。在一般情况下，我们的噪声预测是非常好的协议与声学数据超出峰值频率。
