Yi-Hsin Yen

Study of Liquid Breakup Process in Solid Rocket Motors

In a solid rocket motor, when the aluminum based propellant combusts, the fuel is oxidized into alumina (Al2O3). It tends to agglomerate into molten droplets, impinge on the chamber walls, and then flow along the nozzle wall. Such agglomerates cause erosive damage. The focus of the current research is to characterize the agglomerate flow within the nozzle section by studying the breakup process of the liquid film that flows along the wall of a straight test channel while a relatively higher-speed gas moves over it. We have used an unsteady-flow Reynolds-averaged Navier–Stokes code to investigate the interaction of the liquid film flow with the gas flow. The rate of the wave breakup was characterized by introducing breakup length, Ohnesorge number, and Weber number for various flow conditions. Based on the volume fraction of the liquid, these three numbers are indicators of the level of liquid breakup. We summarize that a larger breakup length relates to a high breakup state of the liquid because the appea...

Design of Solid Rocket Engine

This paper presents both experiment and simulation of alumina molten flow in a solid rocket motor (SRM), when the propellant combusts, the aluminum is oxidized into alumina (Al2O3) which, under the right flow conditions, tends to agglomerate into molten droplets, impinge on the chamber walls, and then flow along the nozzle wall. Such agglomerates can cause erosive damage. The goal of the present study is to characterize the agglomerate flow within the nozzle section by studying the breakup process of a liquid film that flows along the wall of a straight channel while a high-speed gas moves over it. We have used an unsteady-flow Reynolds-Averaged Navier-Stokes code (URANS) to investigate the interaction of the liquid film flow with the gas flow, and analyzed the breakup process for different flow conditions. The rate of the wave breakup was characterized by introducing a breakup-length-scale for various flow conditions based on the Volume Fraction (VF) of the liquid, which is an indicator of a two-phase flow liquid breakup level. A smaller breakup-length-scale means that smaller drops have been created during the breakup process. The study covers the breakup and fluid behaviors based on different gas-liquid momentum flux ratios, different surface tension and viscosity settings, different Ohnesorge numbers (Oh), and different Weber numbers. Both water and molten aluminum flows were considered in the simulation studies. The analysis demonstrates an effective method of correlating the liquid breakup with the main flow conditions in the nozzle channel path.Copyright

Experimental Investigation of Liquid Phase Breakup in Solid Fuel Rockets

Solid rocket motors (SRM)s commonly use aluminized composite propellants. The combustion of aluminum composite propellants in SRM chambers lead to high temperature and pressure conditions resulting in the liquid alumina as a combustion product. The presence of liquid alumina in the flow presents problems such as; chemical erosion of propellant, and mechanical erosion of nozzle. One method of solving the problem of liquid alumina in flow is to change the SRM geometry to induce liquid breakup and suspend the alumina in the flow thus avoiding erosive behavior. To validate numerical simulation methods for geometric breakup induction simulation models of alumina flow can be compared to air and liquid water flows, and the air-liquid water flow models then compared to water-air experimental results. This study investigates experimental geometric induced liquid breakup behavior for the implementation of the alumina flow and nozzle geometry simulation in SRM design. A rectangular chamber was considered for experimental and simulation to explore the air-water flow behavior. The suspension of water was induced with a triangular shaped jump. The resulting two phase flow was examined using photography technique. Significant incitement in the air-water behavior was observed due to geometry modification. Replication of experimental results was simulated with some accuracy.© 2014 ASME

Study of Liquid Breakup Mechanism for Application of Solid Rocket Propulsion

Aluminum-based solid fuel is widely used in solid rocket propulsion system. During combustion, the solid fuel transforms into liquid status oxidant and agglomerate into droplets which impinge to the inner wall of solid rocket motor (SRM) nozzle and result in erosion problem. When a droplet breaks up into smaller size droplet results in less inertia which has a higher chance to following the exhaust gas stream instead of impinging to the inner wall of the nozzle. In this study, the liquid breakup is achieved by changing the fluid property of surface tension. The result of a liquid breakup is obtained using computational fluid dynamics (CFD) simulation of large eddy simulations (LES) and compared with experiment. The result presents the reduction of droplet size by changing the liquid surface tension. The mechanism of droplet breakup is discussed which is found to be due to the lower Laplace pressure or droplet bounding pressure lead to the lower surface tension of the liquid.

Study of Liquid Breakup Mechanism Through a High-Speed Gas Flow

Investigation of liquid breakup mechanism is an important role to improve performance of solid rocket motor (SRM) to reduce the erosion damage near nozzle a throat section. Protection of the nozzle wall could be achieved by enhancing liquid breakup mechanism of the liquid alumina inside combustion chamber before bulk alumina slug erodes the nozzle section. This paper presents a study of air and water two-phase straight channel experiment that simulates the breakup mechanism of alumina. The study of liquid breakup mechanism is carried out by analyzing high-speed camera image through image processing technic during this straight channel two-phase experiment. This image processing extract the particle size and counts data from each frame of high-speed pictures, therefore, we have mass accumulation distribution from different particle size and his information could be useful information for combustion channel design.

Study of Liquid Breakup Process in Solid Rocket Motor Nozzle

Abstract : In a solid rocket motor (SRM), when the aluminum based propellant combusts, the fuel is oxidized into alumina (Al2O3). It tends to agglomerate into molten droplets, impinge on the chamber walls, and then flow along the nozzle wall. Such agglomerates cause erosivedamage. The focus of the current research is to characterize the agglomerate flow within the nozzle section by studying the breakup process of the liquid film that flows along the wall of a straight test channel while a relatively higher-speed gas moves over it. We have used anunsteady-flow Reynolds-Averaged Navier-Stokes code (URANS) to investigate the interaction of the liquid film flow with the gas flow. The rate of the wave breakup was characterized by introducing Breakup-length, Ohnesorge Number (Oh) and Weber Number (We) for various flow conditions. Based on the Volume Fraction (VF) of the liquid, these three numbers are indicators of a two-phase flow liquid breakup level. We could summarize that larger Breakup-length relates to a high break-up state of the liquid since the appearance of droplets contributes to a larger total boundary length during calculation. The Ohnesorge Number is the ratio of the viscous forces to the inertia and surface tension forces, where a large Oh number reduces breakup activity. The Weber Number indicates the ratio of the inertial force to the surface tension force, and a higher Weber Number relates to higher breakup of the two-phase flow.

Study of Two Phase Flow Breakup Behavior for Application to Solid Rocket Motor Nozzle

This paper presents a method of characterizing liquid breakup phenomena using a probability distribution flow pattern and compares CFD results of a straight channel two-phase flow using k-e, SST k-ω and Reynolds Stress Model (RSM). Examination of liquid breakup level is essential for solving erosion phenomenon of solid fuel rocket motor (SRM), due to their use aluminum based solid propellants. During the propellant combustion, the aluminum oxidizes into alumina (Al2O3), which tends to agglomerate into molten droplets under a certain flow conditions. The molten droplets can then impinge on the combustion chamber walls, and flow along the nozzle wall. Such agglomerated aluminum leads to erosive damages to the geometry of de Laval nozzle and reduces the SRM propulsion performance. The volume fraction (VF) contour of the liquid can be used as the raw data for time average flow VF contour of straight channel. The flow shows the probability distribution of two-phase boundary which is mostly controlled by the features of different turbulence models. Those results will be used for future comparison to two-phase flow experiment as model selection reference of SRM two-phase supersonic flow simulation.Copyright

Solid-Fuel Rocket Motor Efficiency Improvement Scheme

Aluminum-based propellants are commonly used in solid rocket motors (SRM) due to their high energy densities. However, the alumina (Al2O3) particles produced during aluminum propellant combustion present performance issues. These particles flow along the combustion chamber to the nozzle in liquid form causing chemical and mechanical erosive damage. This erosive behavior should be avoided in an SRM because it decreases the ballistic performance. Since particle size and trajectory are believed to influence the impingement and accumulation of alumina droplets, which then affects erosive behavior, it is necessary to accurately predict both the particle size and trajectory. For design purposes, accurate prediction must allow for numerical simulation of particle size and trajectory for economic purposes. Recent work in particle size and trajectory using real time radiography (RTR) and numerical simulation demonstrated predictive capabilities for low solid-to-gas. Another study presented image processing methods to effectively process RTR images for larger particle sizes. Since the cost of experimental testing in is very high, due to high temperature and pressure, research in SRM field is more focused on numerical simulation. However, before simulation result could be used in SRM research CFD model validation is necessary. To provide validation for CFD modelling, a water-air two phase strait channel flow with controlled low temperature and pressure is used. In this chapter, two major parts will be covered, which include the comparison between water-air strait channel experiment and CFD results, and a quantification method for both experimental and CFD results is presented.