Junji Nagao

Numerical Study on Characteristics of Real Gas Flow Through a Critical Nozzle

Abstract A critical nozzle is used to measure the mass flow rate of gas. It is well known that the coefficient of discharge of the flow in a critical nozzle is a single function of the Reynolds number. The purpose of the present study is to investigate the real gas effect on discharge coefficient and thermodynamics properties through a critical nozzle by using H2, N2, CH4 and CO2, with the help of a CFD method and to clarify the relationship between mass flow rate of real gas flows at the nozzle throat and Reynolds number numerically. Redlich–Kwong equation of state was employed to consider the force and volume effects of inter-molecules of these gases. Furthermore, conservative equation of vibration energy was applied to investigate the effect of relaxation phenomena involving molecular vibration.

Numerical Study of Air Gas Flow through a Critical Nozzle

A critical nozzle is used to measure the mass flow rate of gas. It is well known that the coefficient of discharge of the flow in a critical nozzle is a single function of the Reynolds number. The purpose of the present study is to investigate high-pressure gas flow of air through a critical nozzle. A computational analysis has been carried out to simulate a critical nozzle flow with real gas effects. A modified Berthelots equation of state is incorporated into the axisymmetric, compressible Navier-Stokes equations. The computational results show that the discharge coefficient for ideal gas assumptions is significantly different from those of the real gas, as the Reynolds number exceeds a certain value. It is also known that the real gas effects appear largely in terms of the compressibility factor and the specific heat ratio, and these become more remarkable as the gas pressure increases. Furthermore, the effects of amplitudes and frequencies of the pressure disturbance on the gas flow through a critical nozzle were investigated numerically. Nomenclature A cross-section area, m Cd discharge coefficient, Cv specific heat at constant volume, J/kg-K D diameter of the critical nozzle throat, m E, F inviscid flux vectors, £, total energy per unit volume, J/m HI source term for axsimmetry, * E-mail: matsuo@me.saga-u.ac.jp. Tel :+81-952-28-8606. Fax:+81-952-28-8587. HI source term for Turbulence, L characteristic length, m J jacobian, m mass flow rate, kg/s p pressure, Pa Pb back pressure, Pa R radius of the critical nozzle, m Ä, S viscous flux vectors, Re Reynolds number, -

Control of the Asymmetric Flow in a Supersonic Nozzle

Several previous works on rocket nozzle flows have revealed thc existencc of the transition from FSS to RSS and the occurrence of asymmetric flow associated with the boundary layer separation, which can cause excessive side-loads of the propulsion system. Thus, it is of practical importance to investigate the asymmetric flow behaviors of the propulsion nozzlc and to develop its control method. In the present study, the asymmetric flow control method using a cavity system was applied to supersonic nozzle flow. Time-dependent asymmetric flow was experimcntally investigated with the rate of change of the nozzle pressure ratio. The results obtained showed that the cavity systcm installed on nozzle wall would be helpful in fixing the unsteady motions of the boundary layer separation, consequcntly reducing the possibility of the occurrence of the asymmetric flow.