Numerical Study Of Pressure Oscillation Of Solid Rocket Motor With Large Length-diameter Ratio

Pressure oscillation is common in the combustion chamber of solid rocket motors,and violent pressure oscillations can lead to catastrophic consequences such as propellant combustion rate changes,abnormal thrust curves,deviation of external ballistic trajectory and even engine structural damage.The large length-diameter ratio solid rocket motor usually work stably,but when the external air flow produces a certain amplitude of disturbance,there is a violent pressure oscillation.Therefore,it is of great significance to study the pressure oscillation problem of external disturbances in the combustion chamber.Based on this background,this paper studies the oscillation characteristics of flow field pressure in the combustion chamber of the engine under external disturbance through theoretical analysis and numerical calculation,and the main contents are as follows:Taking the VKI engine as the model,the acoustic characteristics of the combustion chamber under the working state of cold flow and hot flow of the engine are analyzed,and the influence of different disturbance frequencies and disturbance amplitudes on the pressure oscillation in the combustion chamber under the cold flow and hot flow injection mode of the engine is numerically studied.As the temperature of the injected gas increases,the natural frequency of sound in the combustion chamber gradually increases,and it is gradually sensitive to pressure oscillations caused by external disturbances.When the disturbance frequency is close to the fundamental frequency or frequency doubling,the amplitude in the combustion chamber will increase,and the amplitude of the pressure oscillation excited near the first-order sound frequency is higher than the pressure oscillation amplitude excited near the second-order sound frequency.Under the same disturbance frequency,the amplitude of pressure oscillation in the combustion chamber will further increase as the disturbance amplitude increases.Taking the development process of the Ram missile as the background,the combustion chamber of the initial,middle and late stages of the large-aspect ratio engine tubular charge and the wing column charge was selected as the calculation model,and the influence of different disturbance frequencies on the pressure oscillation in the combustion chamber was numerically studied by combining the acoustic characteristics of the two combustion chambers.When the combustion chamber boundary of the side charge is periodically disturbed,it will have an effect on the pressure oscillation characteristics inside the combustion chamber,and the amplitude in the combustion chamber will be significantly increased when the disturbance frequency is close to the sound frequency,and the disturbance frequency is far from the sound frequency,the amplitude in the combustion chamber will decrease,and the decisive role is the first-order sound frequency.With the advancement of the engine working process,the stability of the combustion chamber of the two charges is getting worse and worse,and the pressure amplitude generated by external disturbances gradually increases.Before engine operation,the amplitude of the combustion chamber pressure oscillation is lower than that of the tubular charge when the foil type charge is disturbed by external disturbance,and the amplitude of the combustion chamber force oscillation of the wing column charge at the end of the working period is higher than that of the tubular charge.The geometry of the engine charge will change the oscillation frequency of the combustion chamber,and the tail of the wing post charge has a damping effect compared with the cavity structure of the tubular charge,which reduces the oscillation amplitude in the combustion chamber.