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Natural Flow Characteristics of Liquid Rocket Engine Turbopump during Startup
Runze Zhou,Hui Chen,Liang Dong,Houlin Liu,Linglin Jiang,Zeyu Chen 한국유체기계학회 2022 International journal of fluid machinery and syste Vol.15 No.3
When the liquid rocket engine turbopump starts, the tank valve opens first before the pump is driven. Due to the tank and hydrostatic pressure, there is a passive flow phenomenon inside the pump called natural flow. The impeller is passively rotated by hydraulic impact, which impacts the stability of the turbopump during the initial startup period. In order to study the unsteady natural flow characteristics of the turbopump, the coupled CFD/6DOF solver is used for simulation and obtaining the variation of rotational speed, flow loss, and torque with time. The characteristics of the turbopump impeller's radial and axial force are analyzed. The internal flow field and pressure pulsation features were investigated. The results show that the rotational speed caused by natural flow increases exponentially with time. Furthermore, the natural flow loss and torque gradually decrease with the increased rotational speed and has distinct pulsation characteristics and periodicity. The backflow phenomenon in the flow channel becomes more complex. The suction chamber and the inducer have a buffering effect on the impact of the incoming flow, making the pressure distribution more uniform. Due to the matching angle and the rotor-stator interference, the pressure pulsation in the guide vanes has distinct sub-harmonic interference during the natural flow process.
Nonexistence and non-decoupling of the dissipative potential for geo-materials
Liu, Yuanxue,Zhang, Yu,Wu, Runze,Zhou, Jiawu,Zheng, Yingren Techno-Press 2015 Geomechanics & engineering Vol.9 No.5
Two fundamental issues exist in the damage theory of geo-material based on the concept of thermodynamics: existence or nonexistence of the dissipation potential, and whether the dissipation potential could be decoupled into a damage potential and a plastic one or not. Thermodynamics theory of elastoplastic damage assumes the existence of dissipation potential, but the presence of dissipation potential is conditional. Based on the dissipation inequality in accord with the second law of thermodynamics, the sufficient and necessary conditions are given for the existence of the dissipation potential separately in total and incremental forms firstly, and proved strictly in theory. With taking advantage of the basic mechanical properties of geo-materials, the nonexistence of the dissipative potential is verified. The sufficient and necessary conditions are also given and proved for the decoupling of the dissipation potential of geo-materials in total and incremental forms. Similarly, the non-decoupling of the dissipation potential has also been proved, which indicates the dissipation potential of geo-materials in total or incremental forms could not be decoupled into a dissipative potential for plasticity and that for damage respectively. The research results for the fundamental issues in the thermodynamics theory of damage will help establish and improve the theoretic basis of elastoplastic damage constitutive model for geo-materials.
Nonexistence and non-decoupling of the dissipative potential for geo-materials
Liu, Yuanxue,Zhang, Yu,Wu, Runze,Zhou, Jiawu,Zheng, Yingren Techno-Press 2015 Geomechanics & engineering Vol.9 No.4
Two fundamental issues exist in the damage theory of geo-material based on the concept of thermodynamics: existence or nonexistence of the dissipation potential, and whether the dissipation potential could be decoupled into a damage potential and a plastic one or not. Thermodynamics theory of elastoplastic damage assumes the existence of dissipation potential, but the presence of dissipation potential is conditional. Based on the dissipation inequality in accord with the second law of thermodynamics, the sufficient and necessary conditions are given for the existence of the dissipation potential separately in total and incremental forms firstly, and proved strictly in theory. With taking advantage of the basic mechanical properties of geo-materials, the nonexistence of the dissipative potential is verified. The sufficient and necessary conditions are also given and proved for the decoupling of the dissipation potential of geo-materials in total and incremental forms. Similarly, the non-decoupling of the dissipation potential has also been proved, which indicates the dissipation potential of geo-materials in total or incremental forms could not be decoupled into a dissipative potential for plasticity and that for damage respectively. The research results for the fundamental issues in the thermodynamics theory of damage will help establish and improve the theoretic basis of elastoplastic damage constitutive model for geo-materials.