Numerical Simulation On Thermoacoustic Oscillation Of Hydrocarbon Fuel At Supercritical Pressures

Liquid rocket engine is an important part of heavy-lift carrier rocket.Compared with solid rocket engine,liquid rocket engine using hydrocarbon fuel as propellant has many advantages such as high specific impulse,adjustable thrust,non-toxic and so on.Thermophysical properties of hydrocarbon fuel is different from that of normal pressure and temperature due to the combustion chamber pressure of liquid rocket engine is higher than the supercritical pressure of hydrocarbon fuel.Hydrocarbon fuel flows through the cooling channel of the combustion chamber wall to cool combustion chamber,and then is injected into combustion chamber for ignition and combustion.The state of hydrocarbon fuel injection into the combustion chamber plays a decisive role in the subsequent process of atomization,mixing and combustion.Thermoacoustic oscillation in the process of cryogenic injection of supercritical hydrocarbon fuel is numerical studied,and thermoacoustic superimposition at supercritical pressures is also investigated in this thesis.The main content of this thesis includes the following parts:(1)The steady and unsteady numerical calculation models at supercritical pressures are established.The reliability of the numerical calculation models such as turbulence model and thermophysical properties calculation method adopted in this thesis is verified by comparing the numerical calculation models with the corresponding experiments.(2)Thermoacoustic oscillation induced by the dramatic change of fluid density resulting from rapid temperature varia-tion during the shear-coaxial injection process at supercritical pressure was numerically simulated.The effects of outlet pressure,high-temperature n-decane flow rate and inlet temperature,low-temperature n-decane injection rate and inlet temperature on the oscillation amplitude and frequency are investigated.The results show that the volume of high-temperature n-decane shrinks drastically when it is cooled rapidly,and the pressure increases first and then decreases rapidly due to the inertial of surrounding high-temperature n-decane,thus thermoacoustic oscillation is generated.The amplitude and frequency of thermoacoustic waves are mainly determined by the thermophysical properties of high-temperature n-decane at different pressures and temperatures: The frequency of thermoacoustic wave increases with the increase of sound speed of high-temperature n-decane;the amplitude of thermoacoustic wave is determined by the relative pressure coefficient of high-temperature n-decane and the rate of temperature change.(3)The conditions for the superimposition of two dimensional thermoacoustic waves to form a standing wave are analyzed based on the thermoacoustic wave generated by supercritical methane induced by periodic temperature.The factors affecting the standing wave frequency,oscillogram of the standing wave and the value of pressure at the antinode are investigated.The results show that when the wave length of the thermoacoustic wave is proportional to the length of the side of the square,the two-dimensional thermoacoustic wave is superimposed to form a standing wave.The value of pressure at the antinode of the standing wave is influenced by the thermophysical properties and the temperature change rate of methane,and the frequency of the standing wave is determined by the sound speed of methane.The oscillogram of standing wave is influenced by the phase lag,wave number and other factors.