Numerical analysis of unsteady multiple jet plume interactions

In order to obtain the analytical method to compute the circumferential strain on a soft pulse separation device (PSD), deformation processes of the middle section of the soft PSD, the medicine propellant grain and the case are simplified into a two-dimensional plane strain state. It is found that the main factors affecting the circumferential strain of the soft PSD are the circumferential strain of the inner surface of the propellant grain and the gap between the soft PSD and the propellant grain. In order to study the failure mechanism of the soft PSD in the double-pulse solid rocket motor (SRM), a two-dimensional axisymmetric finite element method (FEM) model of the stress process of the soft PSD is established. The variation of the strain of the soft PSD with the internal pressure load is obtained. It is found that the excessive circumferential strain is the main reason for the failure of the soft PSD. Comparing the analytical calculations with the FEM results, it can be found that the analytical method value is slightly higher than the FEM value, so the analytical method results can be used to initially estimate the circumferential strain of the soft PSD and then predict the rationality and feasibility of the design scheme. In order to further study the failure mechanism of the soft PSD, a micro-CT test of in situ stretching of the soft PSD material is carried out and the variation of porosity and elongation of the material is studied. The test results showed that when the material elongation is large, the microinterface debonding rapidly expands into a penetrating damage, and the PSD structure fails. The conclusions obtained in this paper can provide a useful reference for the design of double-pulse SRM.

Polymeric composites are widely used in aerospace. One such important use of polymeric composites is the filament-wound composite case for the Solid Rocket Motor (SRM). Environmental conditions expected during flight and other phases of the SRM’s life cycle affect its performance. The performance of SRM, in turn, depends primarily on the composite case and propellant grain. In this study, the performance evaluation of SRM with the composite case is carried out for different environmental conditions. These cases are designed to sustain very high pressure and temperature environments generated due to the combustion of propellant grains and are intended to perform adequately at any time during their service life. The performance evaluation test matrix is formulated considering various expected dynamic and thermal conditions. The small SRM with a composite case is subjected to planned tests as per the matrix, followed by static tests. The pressure versus time data is plotted for all test conditions. The ballistic parameters result of the virgin (without subjecting it to any test) small SRM is considered as a reference for comparative studies with the rest of all other test conditions results. All the ballistic performance test results are also analysed with respect to the pressure-time curve for mission bounds. The analysis of experimental test results reveals that various environmental dynamic conditions like random vibration, acceleration and shock, do not affect the composite case and the ballistic performance of a small SRM. The effect of grain temperature on ballistic performance is also found as expected.

Two phase ow is a challenging subject in the design of solid rocket motors. Not only does it impact the motor performance characteristics, but also inuences the thermal and chemical loads on the motor components. The main particulate found in hybrid and solid rocket combustion is made of aluminum. This study focuses on the continuous development of the TAU Lagrangian particle tracer, including eorts in modeling droplet evaporation, droplet breakup and condensation processes to describe the behavior of the solid particles within the combustion chamber. By combining computationally aordable models, an engineering model able to predict thermal, chemical and mechanical loads is presented. Application to a solid rocket motor engine indicates that this particular modeling approach underpredicts the combustion chamber temperature. Implementation of nucleation and subsequent condensation as a gas phase reaction resulted in chamber temperatures close to the temperature found from equilibrium combustion. While the temperature and species distribution within the chamber largely depend on the modeling of the combustion process, it is shown that the droplet breakup model has a much stronger inuence on the accurate prediction of droplet diameters in the nozzle and subsequent plume.

Summary form only given. Polymer Optical Fibers embedded in the propellant of Solid Rocket Motors are demonstrated for monitoring strains higher than 10%. A new architecture incorporating a closed-loop fiber is proposed and its theoretical behaviour is experimentally verified. The propulsion system of Solid Rocket Motors (SRM) is considered as the most critical system in a guided missile as it powers the missile with predetermined characteristics. A key issue for the safety and reliability of those SRM missiles and consequently for the effective and economic management of missiles' inventory is the efficient Structural Health Monitoring of the energetic propellant grain. This work proposes the use of photonic sensors [1,2] for SRMs' continuous SHM as the preferable solution in such environments, due to their electromagnetic interference immunity and inherent electrical and explosion safe characteristics. Polymer Optical Fibers embedded with excellent bonding characteristics to the propellant material of SRM are demonstrated as an efficient sensing platform. The use of POFs for SHM applications is considered as more robust in terms of installation and operational reliability compared to silica fibers where their fragility leads to a high rejection ratio (around 60%) of unsuccessful installations due to fiber breakage during handling and this ratio is prohibitive when installing fibers in highly expensive units such as SRMs. PMMA POFs used both as jacketed cables or unjacketed bare fibers, were successfully embedded into solid propellant materials and afterwards mechanically loaded in special tensile tests equipment. The experiments were realised with a simple optical setup of a high power LED of 1 mW at 650nm and a photodetector operating at linear regime. By using special primers an excellent bonding between fibers and propellant was achieved allowing thus efficient strain transfer from the energetic material and avoiding relative slipping [3]. Two different configurations were employed, one of axial longitudinal incorporation of the POF along the specimen and the other by incorporation of a fiber loop segment in the longitudinally embedded fiber. The applied strain in the specimen is transferred partially axially to the straight fiber sections while it also allows the geometrical deformation of the embedded loop from the circular to elliptical shape. This deformation results in change of local bend radii along the looped fiber inducing thus additional bend losses. The intrinsic elasticity of the POFs and also the macro-bend originated losses under strain provide monitoring capability for strain and stress much higher than 10%. Additionally resulted plastic deformation of POFs in excessively high strains, is proposed to serve as a data/event logger important for recording materials' stress history.

This work proposes a new effective method to realize variable thrust through discontinuous embedded metal wires in the solid rocket motor (SRM). We aimed to study the influence of discontinuous embedded metal wires on the performance of an SRM with a single-burning-rate grain. A model based on convection heat transfer, heat conduction, and heat radiation was established to calculate the heat transfer in the discontinuous embedded metal wires in the grain, to then obtain the burning rate ratio. Most importantly, a solid rocket motor was designed to verify the feasibility of variable thrust and of the present model prediction, with the embedded silver–nickel alloy wire divided into two segments in the grain. According to the SRM ignition experiment, the silver–nickel alloy wires raised the burning rate of the grain. The pressure varied regularly with changes in the discontinuous embedded metal wires. The theoretical burning rate ratio matched the experimental result well. Based on the verified model, the effects of the burning rate, pressure exponent, burning rate ratio, and number of wires on thrust were investigated. Burning rate, burning rate ratio, and pressure exponent were found to be positively correlated with thrust ratio. The thrust ratio could reach 12.5 when the burning rate ratio was 5. The ability to adjust thrust tended to increase with an increase in the number of wires. This study also provided a method to assess whether the consecutive embedded metal wires had been broken or not. The method using discontinuous embedded metal wires in the grain was proven to be feasible to realize multi-thrusts of single-burning-rate grain, which is a new idea for the design of a multi-thrust SRM.

High-speed motion analysis system could record images up to 12,000fps and analyzed with the image processing system. The system stored data and images directly in electronic memory convenient for managing and analyzing. The high-speed motion analysis system and the X-ray radiography system were established the high-speed real-time X-ray radiography system, which could diagnose and measure the dynamic and high-speed process in opaque. The image processing software was developed for improve quality of the original image for acquiring more precise information. The typical applications of high-speed motion analysis system on solid rocket motor (SRM) were introduced in the paper. The research of anomalous combustion of solid propellant grain with defects, real-time measurement experiment of insulator eroding, explosion incision process of motor, structure and wave character of plume during the process of ignition and flameout, measurement of end burning of solid propellant, measurement of flame front and compatibility between airplane and missile during the missile launching were carried out using high-speed motion analysis system. The significative results were achieved through the research. Aim at application of high-speed motion analysis system on solid rocket motor, the key problem, such as motor vibrancy, electrical source instability, geometry aberrance, and yawp disturbance, which damaged the image quality, was solved. The image processing software was developed which improved the capability of measuring the characteristic of image. The experimental results showed that the system was a powerful facility to study instantaneous and high-speed process in solid rocket motor. With the development of the image processing technique, the capability of high-speed motion analysis system was enhanced.

ABSTRACTThis paper proposes an alternating elliptical impingement chamber in the leading edge of a gas turbine to restrain the cross flow and enhance the heat transfer, and investigates the detailed flow and heat transfer characteristics. The chamber consists of straight sections and transition sections. Numerical simulations are performed by solving the three-dimensional (3D) steady Reynolds-Averaged Navier–Stokes (RANS) equations with the Shear Stress Transport (SST) k– $\omega$ turbulence model. The influences of alternating the cross section on the impingement flow and heat transfer of the chamber are studied by comparison with a smooth semi-elliptical impingement chamber at a cross-flow Velocity Ratio (VR) of 0.2 and Temperature Ratio (TR) of 1.00 in the primary study. Then, the effects of the cross-flow VR and TR are further investigated. The results reveal that, in the semi-elliptical impingement chamber, the impingement jet is deflected by the cross flow and the heat transfer performance is degraded. However, in the alternating elliptical chamber, the cross flow is transformed to a pair of longitudinal vortices, and the flow direction at the centre of the cross section is parallel to the impingement jet, thus improving the jet penetration ability and enhancing the impingement heat transfer. In addition, the heat transfer in the semi-elliptical chamber degrades rapidly away from the stagnation region, while the longitudinal vortices enhance the heat transfer further, making the heat transfer coefficient distribution more uniform. The Nusselt number decreases with increase of VR and TR for both the semi-elliptical chamber and the alternating elliptical chamber. The alternating elliptical chamber enhances the heat transfer and moves the stagnation point up for all VR and TR, and the heat transfer enhancement is more obvious at high cross-flow velocity ratio.

Taylor-Culick flow is of importance on the interior ballistics of solid rocket motor (SRM). The combustion of solid fuel results in the motion of the wall boundary of the flow. Therefore, the understanding of Culick-like flow with a regressing wall plays a significant role in the study of SRM. However, the complex geometry of real fuel surface of SRM leads to considerable difficulty on the analysis and numerical simulation. In this paper, Navier Stokes equations coupled with Level-set equation are resolved to mimic the flows inside the combustion chamber with grain regression of the propellant. The four typical geometrical structure which corresponds to classical propellant grain shapes are simulated. The results demonstrate that the different geometrical structure in associate with flow direction could significantly affect the flow inside the combustion chamber. Besides flow turning could be substantially changed based on different geometrical configuration, isolated vortex could also be introduced under the influence of different injection schemes. Considering both flow turning and vortex play an important role in the combustion instability of the SRM, the geometrical design of grain should be taken additional care except for the traditional requirement of thrust.

Erosive burning rate studies of composite propellants under high cross flow velocities

Solid rocket motors typically include an outer case or shell that houses solid propellant grains. Internal insulation in a solid rocket motor is a layer of heat-barrier material placed between the internal surface of the case and the propellant which. The aim of the present study is to develop and characterize an asbestos-free rubber for use as rocket motor insulator which needs to be taken into account for protecting in the planning of space missions, in their design, and in their operation. Such insulation is based on aramid fiber in the pulp form, alumina and/or silica aerosol as reinforcement for Ethylene Propylene Diene Monomer (EPDM). Different formulations based on these fillers were prepared. The fillers dispersed in the EPDM polymeric matrix to obtain a homogenous master batch for curing. The physical, mechanical (density, hardness, tensile strength and elongation) and thermal properties (effective thermal conductivity) of different compositions were obtained. The ablation resistance of samples with different compositions was measured. Thermo-gravimetric analyses versus reinforcement content were obtained. The effect of changing aramid fiber in the pulp form, alumina and/or silica aerosol volume fractions was studied. For application for solid rocket motor insulation, Reinforcement of EPDM with KP improves the performance of the material with respect to mechanical properties and thermal properties (thermal conductivity) while not improving well the performance with respect to ablation resistance. Using hybrid reinforcement content (KP + Al + Si) inside EPDM improves the performance of EPDM with respect to mechanical properties, thermal properties, ablation resistance and decomposition resistance. The best volume fraction which gives the best performance of the insulation material is 10 Phr KP + 5 Phr Al + 5 Phr Si. A new type of insulation material using the hybrid reinforcements was developed for the first time.

Solid rocket motor design matching the thrust requirement of the overall vehicle has become an exigent task. In the present research, an efficient performance matching optimization approach is proposed and applied to the solid rocket motor design. To obtain reliable solid rocket motor designs, refined performance evaluation is accomplished successfully based on the coupling of the level set grain burnback analysis and one-dimensional ballistic simulation by the time-stepping algorithm. Due to the heavy computing burden of the coupled performance solver, a novel progressive matching optimization approach is proposed. This approach depends on partial but not full-burn thrust profile to eliminate inferior candidates, predict superior candidates, advance the simulation and drive the candidates converging to the specified performance. Validation of the proposed solid rocket motor design approach is carried out by two test cases possessing different thrust requirements, and results indicate that the proposed approach is practical and efficient.

Amid all convective heat transfer augmentation methods employing single phase, jet impingement heat transfer delivers significantly higher coefficient of local heat transfer. The arrangement leading to nine jets in square array has been used to cool a plate maintained at constant heat flux. Numerical study has been carried out using RANS-based turbulence modeling in commercial CFD Fluent software. The turbulent models used for the study are three different “k-ε” models (STD, RNG, and realizable) and SST “k-ω” model. The numerical simulation output is equated with the experimental results to find out the most accurate turbulence model. The impact of variation of Reynolds number, inter-jet spacing, and separation distance has been considered for the geometry considered. These parameters affect the coefficient of heat transfer, temperature, and turbulent kinetic energy related to flow. The local “h” values have been noticed to decline with the rise in separation distance “H/D.” The SST “k-ω” model has been noticed to be in maximum agreement with the experimental results. The average value of heat transfer coefficient “h” reduces from 210 to 193 W/m2K with increase in “H/D” from 6 to 10 at “Re” = 9000 and S/D of 3. As per numerical results, inter-jet spacing “S/D” of 3 has been determined to be the most optimum value.

The structural integrity of the grain is very important for the grain with complex geometry. Large section column structure has its particularity, differs from that of a single column, its length to diameter ratio is large and absolute meat the increase of the thickness, particles of geometric shape and size of the key factors to determine the gas production rate and its change rule of the engine, at the same time, the engine thrust and pressure change with time, particle size determines the volume and weight of the combustion chamber,Therefore, the particle design of solid rocket motor determines the quality design index of the engine to a large extent.In order to improve the efficiency of model optimization, an agent model is established in this paper. The prediction accuracy of the model depends on the distance between prediction points and sample points. The shortest distance hierarchical clustering algorithm is used to improve the prediction accuracy.Through the research, the comprehensive effect of the key factors affecting the structural integrity of the propellant and the law of the influence on the structure and safety margin of the propellant are obtained. The research method and law can provide support for the large solid motor grain design, and provide theoretical reference for the solid rocket motor grain structure multi-parameter optimization design.

While smart manufacturing is viewed as the future of manufacturing, core knowledge about manufacturing is still lacking in various areas and will continue to be one of the main challenges in research and development. In terms of manufacturing process flow, to be able to make justified production control decisions, it is necessary to be able to predict the system's performance and the effects of control actions on the part flow. This amounts to knowing the transient behavior of the production system. However, most of the available studies on production system transients assume Markov models, while the actual production practice often deviates from this assumption. Therefore, in this paper, we carry out preliminary investigation of the transient behavior of production systems with machines characterized by non-Markovian reliability models. Specifically, using discrete-event simulations, we study serial production lines with machines' up- and downtimes modeled by gamma random variables. System properties of several performance metrics during transients are then discussed based on numerical experiments and a Control Theory-based approach. We view this as a first step in understanding the transient behavior of production systems under more realistic mathematical models.

Axial braided C/C composite materials are widely applied in the throat insert of solid rocket motors. It is the key for the development and design of solid rocket motors to characterize accurately the macromechanical properties of the materials. The Jones-Nelson model is employed to characterize the constitutive relation of the axial braided C/C composite material in this paper. The Jones-Nelson model is expanded and modified to characterize the C/C composite under complex load conditions. The typical external load tests were carried out to verify the accuracy. On this basis, the deformation features of the axial braided C/C composite throat insert are investigated during the working process of motors, and the strain of the throat insert during the working process is obtained by FEM. The strain and temperature in the outer surface of the throat insert are measured in the ground test of motors and are compared with the numerical results by FEM to verify the accuracy of the model. The results show that the result calculated based on the modified Jones-Nelson model by FEM is in a good agreement with the test result. It shows that the modified Jones-Nelson model can better describe the constitutive relation of C/C composite materials, and it can be promoted to the engineering application of the throat insert of solid rocket motors.