Numerical simulation research on multiphase flow of aviation centrifugal pump based on OpenFOAM

This paper aims to tackle the calculation efficiency problem raised in the cavitation-flow simulation of the aviation centrifugal pump due to the fading-away interface resulting from the dissipation of numerics used in the phase-change control equation for unstructured-grid multiphase flow,and due to the limitation of flow time-step in whole flow regimes,the control equation of vapor–liquid two-phase flow considering cavitation mass transport is established firstly,modifying the momentum equation by introducing the surface tension,and adding the artificial convective flow to the phase equation to solve the numerical dissipation problem.Secondly,in consideration of the local time step principle and based on the multi-dimensional general limiter algorithm with explicit solutions under the OpenFOAM platform,a solution method of steady-state VOF (Volume of Fluid) model considering cavitation two-phase change is constructed,and the feasibility of this method is verified by NACA hydrofoil and NASA flat plate inducer.Finally,based on the platform developed,the cavitation performance of an aviation centrifugal pump inducer is analyzed.The research results show that the error of the calculated cavitation pressure distribution for NACA hydrofoil between the simulation test and the experimental-test is less than 5%,and the maximum error of calculated cavitation number at pump head dropping for NASA high-speed flat plate inducer between the simulation test and the experimental-test is 2.1%.The cavitation area observed in the simulation test is the same as that obtained in the high-speed photography test.Based on the OpenFOAM simulation method,the position of pump head dropping of the fuel centrifugal pump can be accurately captured.The error of the calculated cavitation number at pump head dropping between the simulation test and the experimental test is about 3.7%,showing high calculation accuracy.

Research Progress on Serum Porphyrin and Chronic Liver Disease

Liver cirrhosis is an important cause of chronic liver cancer.At present,a breakthrough has been achieved in the development of chronic hepatitis C treatment,but there is no effective measure to completely cure chronic hepatitis B.Porphyrins are a class of macromolecular heterocyclic compounds formed by interconnecting the a-carbon atoms of four pyrrole-like substituents through hypomethyl bonds.Porphyrins and their derivatives widely exist in organelles related to energy transfer in organisms.They are mainly involved in the synthesis of heme in human body.Heme is an iron-containing porphyrin compound,15-20% of which is synthesized and utilized in the liver.Studies have found that porphyrin metabolism disorder can occur in patients with chronic liver disease.The early stage of viral hepatitis is accompanied by increased production of porphyrins and their compounds,increased levels of peripheral circulating porphyrins,porphyrin cholestasis,and biochemical changes of free porphyrins which precede the histological changes.The accumulation of serum and liver protoporphyrins and the oxidative stress can cause liver and extrahepatic damage.On the one hand,porphyrin metabolism disorder can aggravate chronic liver disease,and even progress to liver cirrhosis and liver cancer.On the other hand,chronic liver disease can also aggravate porphyrin metabolism disorder,recurrent attacks,and damage to liver and extrahepatic tissues and organs.

考虑状态模糊性的结构非概率可靠性分析

在实际工程中,有时很难明确判断结构所处的状态是安全的还是失效的,基于传统二元状态假设进行的非概率可靠性分析忽略了这种模糊性的存在,过于理想化。针对这一问题,以椭球模型量化不确定变量,引入模糊状态假设代替二元状态假设,开展了考虑状态模糊性的结构非概率可靠性分析研究:根据模糊状态假设,对结构所处的状态进行模糊描述,在此基础上结合无差别原则,发展了非概率模糊可靠度作为考虑状态模糊性时结构非概率可靠性的度量,同时开发出相应的Monte Carlo模拟方法对所提非概率模糊可靠度进行求解;为了克服Monte Carlo方法需要大量调用真实模型而导致的求解效率低下的问题,提出了一种基于主动学习Kriging的求解算法,从而建立了一套高效的能够考虑状态模糊性的结构非概率可靠性分析方法,通过算例和工程实例验证了所提可靠性分析方法的工程实用性。