Numerical Simulation And Experimental Studies On Heat Transfer And Ablation Of Carbon-Phenolic Jet Vanes

The jet vane system is composed of four independently operating jet vanes which are installed in the outlet of a rocket engine nozzle,and it can be used for pitch,yaw and roll control.The main material for manufacturing jet vane is heavy metal alloys,such as,W-Cu or W-Mo alloy.However,high density of these alloys increased the negative quality of rockets.Especially for simple guided rockets by tilted or vertical launching method used for the army,thrust vector control is needed in the initial stage of the trajectory in short time.Therefore,jet vane must be the lighter the better on the premise that the anti-ablation and erosion performance is improved for medium and small caliber rocket systems.In this paper,the carbon-phenolic jet vane was taken as the research object.In view of variable thermal properties and ablation stratification phenomenon of carbon-phenolic in working process,the corresponding heat transfer and ablation models were established as well as numerical simulation methods.The main work is as follows.First,to accurate calculate the heat transfer and ablation of carbon-phenolic,the model of carbon-phenolic's thermal properties varied with working time and temperature in different spaces was proposed based on the pyrolysis kinetics model.The density varied with pyrolysis process of carbon-phenolic was used to invert the volume fraction of phenolic resin,carbon fiber,charring carbon and pore,and then,the transient thermal properties of carbon-phenlic can be concluded.According to the density of material,the stratification of carbon-phenolic during working process was determined.The coupling simulation about heat transfer and volume ablation of carbon-phenolic was realized.The laser ablation experiments of carbon-phenolic samples were carried out to verify the accuracy of the above-mentioned model.The simulation results consistent with the laser ablation test results under nitrogen atmosphere,and the relative error of volume ablation is in the range of-3.9%-7.05%.Second,full-size three-dimensional model of jet vanes was carried out to investigate ablation thermal environment,include steady flow around the jet vane and unsteady fluid-thermal coupling at different deflection angles from 0 to 20 deg.The varies of thermal properties of carbon-phenolic and rocket gas with working time and local temperature was modified by UDF.Heat absorption Pyrolysis and heat absorption process was accomplished through source terms addition method.The flow around jet vane and heat transfer in it at different height section were analyzed.The main conclusion shows that three-dimensional effect of the flow has great influence around tip and root of the jet vane,and the flow around the rest of jet vane is basically the same at different height sections.Third,secondary development on Fluent platform by UDF was carried out to add the source terms in solid region and fluid region.An unsteady fluid-thermal coupling numerical simulation method for jet vane was developed,which takes account of heat absorption process due to pyrolysis and injection process to the mainstream of pyrolysis gas.The study to compare how pyrolysis gas escaped from jet vane influenced the volume ablation and surface temperature was carried out.During the work of carbon-phenolic jet vane,heat flux carried by pyrolysis gas is around 3%?10%to heat flux into jet vane by mainstream.A large amount of energy carried out by pyrolysis gas can reduce the surface temperature of jet vane effectively.Fourth,an unsteady numerical simulation method based on flow-thermal coupling and dynamic mesh was developed to research the boundary regression of carbon-phenolic jet vane due to ablation and erosion.Mass source,momentum source,energy source and species source were added in fluid region adjacent to the wall because of thermo-chemical reaction.The flow field surround carbon-phenolic jet vane due to thermo-chemical ablation and erosion were researched.The conclusion shows that the contribution of thermo-chemical ablation on jet vane's surface to reduce wall temperature is higher than that of pyrolysis gas injection process.Compare the simulation result of erosion to that of thermo-chemical ablation,effect of the former on the jet vane is higher than the latter.Temperature is not the determinant of erosion,but the volume ablation and thermo-chemical ablation caused by high temperature induces the erosion phenomenon.Fifth,the ablation experiments of carbon-phenolic jet vane at different deflection angles were carried out by solid rocket engine.Shape of the jet vane before and after ablation experiment was detailed measured by 3D scanner,and the contours of ablation and erosion after experiment can be obtained.The different position's micromorphology of jet vane at 15deg was obtained by scanning electron microscope.The simulation results and experimental results were analyzed and compared to prove the feasibility of the numerical simulation method.It can be speculated that the carbon-phenolic jet vane can satisfy the requirement of 20?30%surface ablation rate around 1.5s working time according to experimental result.Carbon-phenolic jet vane can be used in thrust vector control in initial stage of the trajectory for simple guided rockets,to reduce the negative quality and the cost effectively.