NUMERICAL SIMULATION OF COMBUSTION OF THE COMPOSITE SOLID PROPELLANT CONTAINING BIDISPERSED BORON POWDER

A problem of combustion of the composite solid propellants containing various powders of metals and non-metals is relevant in terms of studying the effect of various compositions of powders on the linear rate of propellant combustion. One of the lines of research is to determine the effect of the addition of a boron powder on the burning rate of a composite solid propellant. This work presents the results of numerical simulation of combustion of the composite solid propellant containing bidispersed boron powder. Physical and mathematical formulation of the problem is based on the approaches of the mechanics of two-phase reactive media. To determine the linear burning rate, the Hermance model of combustion of composite solid propellants is used, based on the assumption that the burning rate is determined by mass fluxes of the components outgoing from the propellant surface. The solution is performed numerically using the breakdown of an arbitrary discontinuity algorithm. The dependences of the linear burning rate of the composite solid propellant on the dispersion of the boron particles and gas pressure above the propellant surface are obtained. It is shown that the burning rate of the composite solid propellant with bidispersed boron powder changes in contrast to that of the composite solid propellant with monodispersed powder. This fact proves that the powder dispersion should be taken into account when solving the problems of combustion of the composite solid propellants containing reactive particles.

A New Erosive Burning Model of Solid Propellant Based on Heat Transfer Equilibrium at Propellant Surface

Erosive burning refers to the augmentation of propellant burning rate appears when the velocity of combustion gas flowing parallel to the propellant surface is relatively high. Erosive burning can influence the total burning rate of propellant and performance of solid rocket motors dramatically. There have been many different models to evaluate erosive burning rate for now. Yet, due to the complication processes involving in propellant and solid rocket motor combustion, unknown constants often exist in these models. To use these models, trial-and-error procedure must be implemented to determine the unknown constants firstly. This makes many models difficult to estimate erosive burning before plenty of experiments. In this paper, a new erosive burning rate model is proposed based on the assumption that the erosive burning rate is proportional to the heat flux at the propellant surface. With entrance effect, roughness, and transpiration considered, convective heat transfer coefficient correlation proposed in recent years is used to compute the heat flux. This allows the release of unknown constants, making the model universal and easy to implement. The computational data of the model are compared with different experimental and computational data from different models. Results show that good accuracy (10%) with experiments can be achieved by this model. It is concluded that the present model could be used universally for erosive burning rate evaluation of propellant and performance prediction of solid rocket motor as well.

Imaging Aluminum Particles in Solid-Propellant Flames Using 5 kHz LIF of Al Atoms

Laser-induced fluorescence imaging of aluminum atoms (Al-PLIF) is used to analyze the spatio-temporal behavior of aluminized solid propellant combustion. Using alternating LIF and chemiluminescence emission images of the particles in the gaseous and liquid phase evolving close to and far above the dynamically varying propellant surface, sequences of images were recorded and analyzed. The good sensitivity achieved enabled us to track the dynamics of the flame in the vicinity of particles detected all along the flame extension and up to 1.5 MPa. Analysis of wide-field images enabled droplet velocity measurements due to the high LIF sampling rate (5 kHz). The observed typical plume structures were in good agreement with alumina-formation prediction and previous shadowgraphy visualization. High-resolution sequences of images showed gaseous distribution behavior around the molten particles. The Al vapor phase was thus found to extend between 3 and 6.5 radii around the particles. Particle detachment dynamics were captured just above the propellant surface.

Flame response of solid propellant AP/Al/HTPB to a longitudinal acoustic wave

This paper is devoted to an experimental work which consists of the analysis of the flame of a small solid propellant sample, AP/Al/HTPB, subjected to a longitudinal acoustic wave. Experiments were conducted in a closed tube under two mean pressures: 1 and 2.5 MPa. The qualitative and quantitative analysis of the flame snapshots, using a microscope and a high-speed camera, revealed that the acoustic wave created at the end of the chamber by a pulser system strongly affects the flame and the combustion products dynamic above the solid propellant surface, namely, the flame and the hot products oscillate around a line perpendicular to the propellant surface. This dynamic of the hot gas disturbs the local burning rate and the regression surface profile. Thus, the thrust and the burning duration will change, therefore, the flight path of the rocket may shift and can lead to failure of the mission.

Star Grain Regression under Spin Induced Acceleration Effect

Spinning is used in some of solid rocket motors to increase the flight trajectory precision or for stability requirements. The angular acceleration due to the spin effect increases the burning rate of solid propellant and changes the motor performance by increasing the operating pressure and decreasing the burning time. So it is important to know the grain regression taken place in the solid propellant rocket motor in the acceleration field. In this study, we represent the grain regression analysis of two-dimensional axis-symmetric star grain configuration of the solid propellant rocket motor under spin induced acceleration effect to study how the spin affects on the internal ballistics of the solid rocket motor. Grain regression is done by two methods - geometrical approach and numerical approach. The burning rates on the propellant surface are different with its radial distance, acceleration vector angle and surface slope when the rocket is spinning. With the different burn rates on the propellant surface, the propellant surface perimeter and port area are computed by using the numerical method, and the results are compared with that of constant burn rate.

Technical Brief: Asymptotic Temperature Distribution in a Simulated Combustion Chamber

In an axisymmetric model of a solid rocket motor, a cylindrical combustion chamber with porous walls is considered. For a posited range of operating parameters, the energy equation is perturbed and linearized using the dimensionless Péclet number. The possibility of circumventing chemical reactions while retaining the essential physics of the problem is explored. This is accomplished by artificially introducing a distributed heat source above the propellant surface. The resulting energy equation is then solved to zeroth order. The analytical solution and corresponding temperature maps are verified qualitatively using comparisons with numerical simulations of the combustion chamber.

New Method to Determine the Velocities of Particles on a Solid Propellant Surface in a Solid Rocket Motor

Use of aluminized composite solid propellants and submerged nozzles are common in solid rocket motors (SRM). Due to the generation of slag, which injects into a combusted gas flow, a two-phase flow pattern is one of the main flow characteristics that need to be investigated in SRM. Validation of two-phase flow modeling in a solid rocket motor combustion chamber is the focus of this research. The particles’ boundary conditions constrain their trajectories, which affect both the two-phase flow calculations, and the evaluation of the slag accumulation. A harsh operation environment in the SRM with high temperatures and high pressure makes the measurement of the internal flow field quite difficult. The open literature includes only a few sets of experimental data that can be used to validate theoretical analyses and numerical calculations for the two-phase flow in a SRM. Therefore, mathematical models that calculate the trajectories of particles may reach different conclusions mainly because of the boundary conditions. A new method to determine the particle velocities on the solid propellant surface is developed in this study, which is based on the x-ray real-time radiography (RTR) technique, and is coupled with the two-phase flow numerical simulation. Other methods imitate the particle ejection from the propellant surface. The RTR high-speed motion analyzer measures the trajectory of the metal particles in a combustion chamber. An image processing software was developed for tracing a slug particle path with the RTR images in the combustion chamber, by which the trajectories of particles were successfully obtained.