Total Impulse Research Articles

Performance and High-Speed Characterization of a 100-kW Nested Hall Thruster

The performance of a three-channel, 100-kW nested Hall thruster was evaluated on xenon propellant for total powers up to 102 kW. The thruster demonstrated stable operation in all seven available channel combinations at discharge voltages from 300 to 500 V and three different current densities. The resulting test matrix contained forty-six unique conditions ranging from 5 to 102 kW total power and 16 to 247 A discharge current. At each operating condition, thrust, specific impulse, and efficiency were characterized. All seven channel combinations showed similar performance at a given discharge voltage and current density. The largest thrust recorded was at discharge voltage. Total efficiency and specific impulse ranged from 0.54 to and from 1800 to 2650 s s, respectively. Discharge current oscillations were also characterized with peak-to-peak values and with high-speed camera analysis, which provide insight into how the discharge channels oscillate and how those oscillations are affected by the presence of other operating channels. These results are discussed in the context of differences between single- and multichannel operation, as are the implications for the general viability of nested Hall thruster technology for future mission applications.

The protective mechanism of pyramid lattice on submarine subjected to undex

<p indent=0mm>The pyramid lattice sandwich shell is applied to the non-pressure hull of conventional submarine to reduce the damage when it is attacked by torpedo in close range. The design of pyramid lattice sandwich shell on conventional submarine is put forward. MSC.NASTRAN was used to study the anti-high hydrostatic performance of submarine hull after pyramid lattice sandwich shell was installed. The simulation results show that the improved submarine cabin structure is in a safe range under the designed water depth. Then MSC.DYTRAN was used to study the anti-explosion effect of the pyramid lattice sandwich shell as the outer protective structure of submarine. The results show that when the <sc>100 kg</sc> TNT charge explodes at <sc>3 m</sc> on the side of the submarine cabin, taking the damaged deformation as evaluation parameter, the anti-explosion performance of the submarine’s pressure hull mounted with pyramid lattice sandwich shell is 69.7% better than that of conventional submarine. The anti-explosion performance of the shell plate and upper deck was improved by 49.8% and 55.8%, respectively. Compared with solid plates, when the fluid-solid coupling parameter is greater than 10 and the ratio of core strength to peak pressure of shock wave is less than 0.15, the core layer can reduce the total incident impulse by more than 60%. The pyramid lattice sandwich shell used in submarine can not only meet the conditions of high hydrostatic pressure, but also greatly improve the anti-explosion performance of submarine hull structure, which has significant application value.

Superior performance of quaternary NC/GO/Al/KClO4 nanothermite for high speed impulse small-scale propulsion applications

Nanothermites are considered promising energetic materials and a key to develop new technologies in the field of energetics and propulsion. However, relatively low peak pressure, smaller thrust output, and incomplete combustion represent some of the potential problems associated with nanothermites. In this study to improve the combustion performance of nanothermites, varying quantities of nitrocellulose (NC) were introduced to produce the quaternary NC/GO/Al/KClO4 nanothermite using facile electrospinning. The morphology of nanothermites was characterized by SEM-EDX which confirmed that the nanoparticles were homogeneously dispersed without agglomeration. The combustion behavior of the composites was evaluated by igniting the samples at different packing densities (%TMD) in open acrylic tubes within a reaction chamber and using a 3.5 W continuous wave laser. High speed imaging captured the flame propagation and differential scanning calorimetry (DSC) was used to assess thermal behavior and energy output. Finally, for propulsion characterization, a small-scale test motor (STM) with a converging/diverging nozzle was used to evaluate the combustion performance of the prepared samples. In general, thrust output, specific and volumetric impulses (ISP and ISV), and total heat released exhibit remarkable enhancement with the addition of NC. Specifically, the total impulse (IFT) and ISP peaked at 5% NC/GO/Al/KClO4 at ~ 50% TMD, with IFT of 19.9 mN.s and ISP of 203.2 s. These are improvements of over 50% compared to the sample without NC (13.4 mN.s and 137.4 s). The ignition delay time and the power required to ignite the NC-enriched mixture is increased, but a sufficiently fast response is maintained for practical applications. Thermal analysis implies that addition of NC introduced another step to the GO/Al/KClO4 reaction: a gas− solid phase and liquid−liquid phase diffusion reaction, with the liquid−liquid phase reaction increasing with NC percentage. These results suggest that electrospinning is a simple technique for preparation of quaternary nanothermites that results in enhanced combustion performance and an improved suitability for small-scale propulsion applications.

Modular Impulsive Green Monopropellant Propulsion System (MIMPS-G): For CubeSats in LEO and to the Moon

Green propellants are currently considered as enabling technology that is revolutionizing the development of high-performance space propulsion, especially for small-sized spacecraft. Modern space missions, either in LEO or interplanetary, require relatively high-thrust and impulsive capabilities to provide better control on the spacecraft, and to overcome the growing challenges, particularly related to overcrowded LEOs, and to modern space application orbital maneuver requirements. Green monopropellants are gaining momentum in the design and development of small and modular liquid propulsion systems, especially for CubeSats, due to their favorable thermophysical properties and relatively high performance when compared to gaseous propellants, and perhaps simpler management when compared to bipropellants. Accordingly, a novel high-thrust modular impulsive green monopropellant propulsion system with a micro electric pump feed cycle is proposed. MIMPS-G500mN is designed to be capable of delivering 0.5 N thrust and offers theoretical total impulse Itot from 850 to 1350 N s per 1U and &gt;3000 N s per 2U depending on the burnt monopropellant, which makes it a candidate for various LEO satellites as well as future Moon missions. Green monopropellant ASCENT (formerly AF-M315E), as well as HAN and ADN-based alternatives (i.e., HNP225 and LMP-103S) were proposed in the preliminary design and system analysis. The article will present state-of-the-art green monopropellants in the (EIL) Energetic Ionic Liquid class and a trade-off study for proposed propellants. System analysis and design of MIMPS-G500mN will be discussed in detail, and the article will conclude with a market survey on small satellites green monopropellant propulsion systems and commercial off-the-shelf thrusters.

Reconstructing an epigenetic landscape using a genetic pulling approach.

Cells use genetic switches to shift between alternate stable gene expression states, e.g., to adapt to new environments or to follow a developmental pathway. Conceptually, these stable phenotypes can be considered as attractive states on an epigenetic landscape with phenotypic changes being transitions between states. Measuring these transitions is challenging because they are both very rare in the absence of appropriate signals and very fast. As such, it has proved difficult to experimentally map the epigenetic landscapes that are widely believed to underly developmental networks. Here, we introduce a nonequilibrium perturbation method to help reconstruct a regulatory network's epigenetic landscape. We derive the mathematical theory needed and then use the method on simulated data to reconstruct the landscapes. Our results show that with a relatively small number of perturbation experiments it is possible to recover an accurate representation of the true epigenetic landscape. We propose that our theory provides a general method by which epigenetic landscapes can be studied. Finally, our theory suggests that the total perturbation impulse required to induce a switch between metastable states is a fundamental quantity in developmental dynamics.

Parameter characterization of a buried mine blast event with further emphasis on sympathetic detonation and layered soil bed conditions

The presented work documents the results of a comprehensive sensitivity study of the structural response of a military vehicle subjected to the impulse from a buried charge using the discrete particle method (DPM) to model the soil and high explosive (HE) coupled to a finite-element solver for the structure. Eighteen different process and numerical parameters were studied. Each of the numerical results was compared with a base model to see the influence of the considered parameter. The structure in the base model was the TARDEC Generic Vehicle Hull and the response parameter was chosen to be the total blast impulse (TBI) on the structure. The non-linear transient dynamic explicit finite-element solver used for the analysis was the IMPETUS Afea Solver®. The study includes soil characteristics and charge related parameters, such as size, type, geometry, and location. The depth of burial (DOB) and number of discrete particles were also considered in the study. Further, different numerical parameters were included. The results provide a good understanding of process and numerical parameters when modeling buried charges with a coupled finite-element model (FEM) and DPM approach. As a natural extension of the sensitivity study the effect of a layered soil bed is investigated, the topsoil either being dry or wet soil. Further, it is illustrated how to model a sympathetic detonation where the detonation of one improvised explosive device (IED) generates a pressure that results in the detonation of a second IED.

Design and In-orbit Demonstration of REGULUS, an Iodine electric propulsion system

REGULUS is an Iodine-based electric propulsion system. It has been designed and manufactured at the Italian company Technology for Propulsion and Innovation SpA (T4i). REGULUS integrates the Magnetically Enhanced Plasma Thruster (MEPT) and its subsystems, namely electronics, fluidic, and thermo-structural in a volume of 1.5 U. The mass envelope is 2.5 kg, including propellant. REGULUS targets CubeSat platforms larger than 6 U and CubeSat carriers. A thrust T = 0.60 mN and a specific impulse Isp = 600 s are achieved with an input power of P = 50 W; the nominal total impulse is Itot = 3000 Ns. REGULUS has been integrated on-board of the UniSat-7 satellite and its In-orbit Demonstration (IoD) is currently ongoing. The principal topics addressed in this work are: (i) design of REGULUS, (ii) comparison of the propulsive performance obtained operating the MEPT with different propellants, namely Xenon and Iodine, (iii) qualification and acceptance tests, (iv) plume analysis, (v) the IoD.

Near-field spatial and temporal blast pressure distributions from non-spherical charges: Horizontally-aligned cylinders

Research into the characterisation of blast loading on structures following the detonation of a high explosive commonly assumes that the charge is spherical. This has the advantage of simplifying experimental, analytical and computational studies. In practice, however, designers of protective structures must often consider explosive threats which have other geometric forms, which has significant influence on the loading imparted to structures very close to the explosion source. Hitherto, there has been little definitive experimental investigation of the ‘near-field’ blast load parameters from non-spherical explosive charges and studies that have been conducted are usually confined to measurement of the total impulse imparted to a target. Currently, a detailed understanding of the development of loading on a target, necessary to fully inform the design process and appraise the efficacy of predictions from computational models, is lacking. This article, the first part of a wider investigation into these geometrical effects, details work conducted to address this deficiency. Results are presented from an experimental study of loading from detonations of cylindrical charges, set with the longitudinal axis parallel to an effectively rigid target, instrumented to facilitate the capture of the spatial and temporal evolution of the loading at different radial and angular offsets from the charge. These results are compared against loads from spherical charges and the effect of charge shape is identified. Significant differences are observed in the mechanisms and magnitude of loading from cylindrical and spherical charges, which is confirmed through the use of numerical analysis. The overall study provides insights which will assist the future design of effective protection systems.

Ground reaction forces and muscle allometry in monitor lizards (Varanidae) with implications for the scaling of locomotion in sprawling tetrapods

Geometric scaling predicts a major constraint for legged, terrestrial locomotion. Locomotor support requirements scale isometrically with body mass (α M1), while force generation capacity should scale α M2/3 as it depends on cross-sectional area. Mammals compensate with more erect postures at larger sizes, but it remains unknown how sprawling tetrapods deal with this constraint. Varanid lizards are an ideal group to address this question because they cover an enormous body size range while maintaining similar posture and body proportions. This study reports the scaling of ground reaction forces and duty factor from varanid lizards ranging from 7-37,000 g. Impulses (α M0.96-1.34) and peak forces (α M0.72-0.98) scaled higher than expected. Duty factor scaled α M0.04 and was higher in the hindlimb than in the forelimb. The proportion of vertical impulse to total impulse increased with body size, and impulses decreased while peak forces increased with speed. Muscle parameters (fascicle length, muscle mass, and physiological cross-sectional area) were also found to scale with positive allometry in varanids, suggesting that varanid lizards respond to predicted biomechanical demands of increased body size with both anatomical and kinematic adjustments. Peak forces scale (> M2/3), suggesting that muscle and skeletal strength increases with positive allometry, but (< M1), suggesting that larger varanids also increase duty factor to spread body support over a longer period. These results provide insight into the biomechanics of extinct, sprawling megafauna.

A Method for Estimation of Blast Performance of RDX‐IPN‐Al Annular Thermobaric Charges

AbstractThe objective of this research was to develop and to experimentally validate a method to predict the blast performance of thermobaric annular charges based on isopropyl nitrate‐aluminium and RDX‐isopropyl nitrate‐aluminium. Overpressure and thermal output were investigated in open air using piezoelectric pressure transducers, high speed visible and infrared imaging. Prediction of the explosive transformation of the annular thermobaric charge was computed by thermochemical code EXPLO5® using the Chapman‐Jouguet (ideal detonation) and non‐ideal Wood and Kirkwood (WK) detonation model. The Jones‐Wilkins‐Lee (JWL) parameters obtained in the calculations were used in hydrocode numerical simulation using AUTODYN® in order to predict the incident overpressure, total impulse and arrival time. Additional energy attributed to aluminium afterburning was used in order to simulate the post‐combustion phase. For isopropyl nitrate‐aluminium based charges, both BKW and WK models estimate correctly the peak overpressure and arrival time, while the total impulse was more accurately calculated by WK non‐ideal detonation model. For the RDX‐containing formulation, the prediction of peak overpressure, total impulse and arrival time are in agreement with the predictions obtained using WK non‐ideal detonation model with additional energy. The performances of the investigated thermobaric charges were compared with an equivalent mass charge of TNT, confirming both the expected higher total impulse and higher peak overpressures in the case of RDX‐isopropyl nitrate‐aluminium based thermobaric charges. Thermal measurements highlighted two distinct phases, an anaerobic phase and the post combustion of the thermobaric compositions. In terms of thermal output, the RDX‐isopropyl nitrate‐aluminium thermobaric based charge manifests superior performances.

Scaling the response of armor steel subjected to blast loading

The influence of the strain-rate effect of steel and the mechanical effect of explosive shock load are both key problems to achieving the similarity scaling of a steel plate structure under blast loading. In this research, the scaling of the dynamic response of strain-rate sensitive armor steel subjected to air blast loading was studied further. First, the specific impulse was defined, and the influence of the strain-rate and the geometric scaling ratio on the specific impulse correction factor was analyzed with dimensional analysis. Then, a real air explosion test was carried out to study the response of a full-size armor steel plate during a blast, and the Johnson-Cook constitutive parameters of the armor steel material were obtained using split Hopkinson pressure bar experimental technology, with which the accurate scaling base mode was established. Furthermore, by employing the correction factors of the specific impulse and the total impulse calculated by empirical equations, two correction methods were proven: I-correcting the stand-off distance and II-correcting the charge mass. Then, the relationships between the specific impulse, the total impulse, the stand-off distance and the charge mass are discussed, based on which the explosion load boundary corresponding to the geometric scaling coefficient was determined. The results showed that the prediction of the corrected scaled model was in good agreement with the experimental results, and both methods could achieve the scaling of the response of the armor steel plate subjected to blast loading.

The sun diver: Combining solar sails with the Oberth effect

A highly reflective sail provides a way to propel a spacecraft out of the solar system using solar radiation pressure. The closer the spacecraft is to the Sun when it starts its outward journey, the larger the radiation pressure and so the larger the final velocity. For a spacecraft starting on the Earth's orbit, closer proximity can be achieved via a retrograde impulse from a rocket engine. The sail is then deployed at the closest approach to the Sun. Employing the so-called Oberth effect, a second, prograde, impulse at closest approach will raise the final velocity further. Here, I investigate how a fixed total impulse (Δv) can best be distributed in this procedure to maximize the sail's velocity at infinity. Once Δv exceeds a threshold that depends on the lightness number of the sail (a measure of its sun-induced acceleration), the best strategy is to use all of the Δv in the retrograde impulse to dive as close as possible to the Sun. Below the threshold, the best strategy is to use all of the Δv in the prograde impulse and thus not to dive at all. Although larger velocities can be achieved with multi-stage impulsive transfers, this study shows some interesting and perhaps counter-intuitive consequences of combining impulses with solar sails.

Performance Analysis of a Dual-Fuel Sugar Based Solid Rocket Propellant

The effects of dual-fuel on improving the ballistic efficiency of a low energy sugar-based solid rocket propellant were investigated in this paper. This was achieved by establishing a threshold proportion of sucrose to sorbitol that provided the highest ballistic efficiency, using a beam load cell (model single-point 2,000 kg linearly defined by 0-20 kN force, with ±.005 percent precision). Seven different propellant formulations were prepared, loaded into the rocket motor and tested for performance. The major performance parameters of interest were the thrust, total impulse, burn time, delivered specific impulse, delivered characteristic velocity, and the chamber pressure. The formulations tested were potassium nitrate–sucrose propellant (65% KNO3 and 35% sucrose (C12H22O11)) (KNSU); potassium nitrate-sorbitol propellant (65% KNO3 and 35% sorbitol (C6H14O6)) (KNSB); modified potassium nitrate-sucrose propellant (65% KNO3, 32% sucrose (C12H22O11)), and 3% carbon (C) (MODKNSU); potassium nitrate-sucrose-sorbitol propellant (65% KNO3, 25% sucrose (C12H22O11)), and 10% sorbitol (C6H14O6) (KNERK); potassium nitrate-sucrose-sorbitol-carbon propellant (65% KNO3, 24% sucrose (C12H22O11), 10% sorbitol (C6H14O6), and 1% carbon (C)) (MODKNERK); and finally a propellant made from KNO3, sucrose (C12H22O11), sorbitol (C6H14O6), carbon (C) and iron II oxide(Fe2O3) combinations in 65, 30, 3, 1, 1% proportion respectively. The novel result obtained from these experiments was applied to boost the performance of a KNSB rocket propellant motor during a rocket launch experiment. Both static and dynamic rocket motor internal ballistic parameters were then compared. The measured delivered motor average thrust and the effective propellant burn times were recorded as: (164.15N, 3.97s); (102.95N, 6.53s); (65.66N, 9.38s); (79.09N, 3.77s); (243.98N, 3.77s) and (92.6N, 5.89s) respectively. The MODKNERK, was established to produce a most efficient motor and with the full delivery of its ballistic energy. It was also established, that the ballistic and rocket motor efficiency of a lower energy rocket motor can be improved by starting the ignition of such motor with fast burning dual-fuel rocket propellant (MODKNERK).

Performance Analysis of a Dual-Fuel Sugar Based Solid Rocket Propellant

The effects of dual-fuel on improving the ballistic efficiency of a low energy sugar-based solid rocket propellant were investigated in this paper. This was achieved by establishing a threshold proportion of sucrose to sorbitol that provided the highest ballistic efficiency, using a beam load cell (model single-point 2,000 kg linearly defined by 0-20 kN force, with ±.005 percent precision). Seven different propellant formulations were prepared, loaded into the rocket motor and tested for performance. The major performance parameters of interest were the thrust, total impulse, burn time, delivered specific impulse, delivered characteristic velocity, and the chamber pressure. The formulations tested were potassium nitrate–sucrose propellant (65% KNO3 and 35% sucrose (C12H22O11)) (KNSU); potassium nitrate-sorbitol propellant (65% KNO3 and 35% sorbitol (C6H14O6)) (KNSB); modified potassium nitrate-sucrose propellant (65% KNO3, 32% sucrose (C12H22O11)), and 3% carbon (C) (MODKNSU); potassium nitrate-sucrose-sorbitol propellant (65% KNO3, 25% sucrose (C12H22O11)), and 10% sorbitol (C6H14O6) (KNERK); potassium nitrate-sucrose-sorbitol-carbon propellant (65% KNO3, 24% sucrose (C12H22O11), 10% sorbitol (C6H14O6), and 1% carbon (C)) (MODKNERK); and finally a propellant made from KNO3, sucrose (C12H22O11), sorbitol (C6H14O6), carbon (C) and iron II oxide(Fe2O3) combinations in 65, 30, 3, 1, 1% proportion respectively. The novel result obtained from these experiments was applied to boost the performance of a KNSB rocket propellant motor during a rocket launch experiment. Both static and dynamic rocket motor internal ballistic parameters were then compared. The measured delivered motor average thrust and the effective propellant burn times were recorded as: (164.15N, 3.97s); (102.95N, 6.53s); (65.66N, 9.38s); (79.09N, 3.77s); (243.98N, 3.77s) and (92.6N, 5.89s) respectively. The MODKNERK, was established to produce a most efficient motor and with the full delivery of its ballistic energy. It was also established, that the ballistic and rocket motor efficiency of a lower energy rocket motor can be improved by starting the ignition of such motor with fast burning dual-fuel rocket propellant (MODKNERK).

The scaling of ground reaction forces and duty factor in monitor lizards: implications for locomotion in sprawling tetrapods.

Geometric scaling predicts a major challenge for legged, terrestrial locomotion. Locomotor support requirements scale identically with body mass (α M1), while force-generation capacity should scale α M2/3 as it depends on muscle cross-sectional area. Mammals compensate with more upright limb postures at larger sizes, but it remains unknown how sprawling tetrapods deal with this challenge. Varanid lizards are an ideal group to address this question because they cover an enormous body size range while maintaining a similar bent-limb posture and body proportions. This study reports the scaling of ground reaction forces and duty factor for varanid lizards ranging from 7 g to 37 kg. Impulses (force×time) (α M0.99-1.34) and peak forces (α M0.73-1.00) scaled higher than expected. Duty factor scaled α M0.04 and was higher for the hindlimb than the forelimb. The proportion of vertical impulse to total impulse increased with body size, and impulses decreased while peak forces increased with speed.

Multidisciplinary Design of Bipropellant Propulsion System in Three Methods, Optimal Design, Reliability Based Design and Optimal Reliability Based Design

The need to improve the reliability and safety requirements, has led to increasingly utilization of reliability based design approaches. In this study, reliability based multidisciplinary design optimization for a bipropellant propulsion system has been investigated. The objective function is minimizing the total system mass and design constraints are the total impulse and the temperature of the wall of the combustion chamber. Monte Carlo simulation methodology is used to apply uncertainties in the problem and to show the reliability of the system under these uncertainties. The mass, functional and geometric results of the bipropellant propulsion system are differentiated for optimal design, reliability based design and optimal reliability based design. Then, considering the results, the concepts and definitions of design methods are compared and discussed and it is shown that the reliability based multidisciplinary optimization while having the desired mass, has high reliability.

Impulse Bit Measurements from Metal Plasma Thruster

A torsional thrust stand, calibrated for impulse bits in the range of , was used to measure impulse bits from a metal plasma thruster. Impulse data were obtained on roughly 1400 shots, with metal plasma thruster targets of molybdenum, niobium, palladium, aluminum, and carbon. Model predictions (based on a simple circuit model and published plasma parameters) were validated by data from the calibrated torsional thrust stand. Over a typical 50-shot firing sequence, the impulse bits measured showed a coefficient of variation of approximately 5%. This implies that individual impulse bits of about can be imparted to a satellite with variation about the mean in a total impulse burst of . For a 20 kg satellite, this would result in a velocity increment of just , enabling very precise attitude control and fine positioning control of nano- and microsatellites. The metal plasma thruster uses solid metal propellant and hence requires no liquids, gases, flow valves, or flow controls and has no moving parts. Total impulse approximately provides orbit raising and drag compensation capability.

Numerical Study on Performance Effect of Burning-rate Ratio in Nozzleless Rocket Motor with Series Dual Burning Rate Grain

ABSTRACT The application of series dual burning rate grain can improve specific impulse of nozzleless solid rocket motor (NSRM). In this paper, burning-rate ratio is the ratio of main propellant burning rate and nozzle propellant burning rate in dual burning rate grain, which has significant influence on NSRM performance. Focusing on relationship between burning-rate ratio and motor performance, internal ballistics simulation of NSRM with different burning-rate ratios has been carried out. Results show that, with the increase of burning-rate ratio, total impulse grows monotonically, while maximum head pressure has two variation stages – the stable stage and the increasing stage. By analyzing the head pressure curves, it is known that maximum head pressure is almost equal to the higher one of initial stage head pressure (p1) and combustion ending stage head pressure (p2). Relationship between p2/p1 and burning-rate ratio has been established by linear fitting, and the critical burning-rate ratio, which is the maximum burning-rate ratio to ensure that maximum head pressure almost is kept invariant, has been obtained. Critical burning-rate ratio has no significant change when geometry size remains invariant. Utilizing critical burning-rate ratio in NSRM with series dual burning rate grain, specific impulse can be enhanced with nearly no sacrifice of maximum head pressure performance. These results can provide references for NSRM designing and optimizing.

Performance of drag force models for shock-accelerated flow in dense particle suspensions

Models for prediction of drag forces within a particle cloud following shock-acceleration are evaluated with the aid of results from particle-resolved simulations in order to quantify how much the disturbances introduced by the proximity of nearby particles affect the drag forces. The drag models evaluated here consist of quasi-steady forces, undisturbed flow forces, inviscid unsteady forces, and viscous unsteady forces. Two dense particle curtain correction schemes to these forces, based on volume fraction and input velocity, are also evaluated. The models are tested in two ways; first they are evaluated based on volume-averaged flow fields from particle-resolved simulations; secondly, they are applied in Eulerian-Lagrangian simulations, and the results are compared to the particle-resolved simulations.The results show that both correction schemes significantly improve the particle force predictions, but the average total impulse on the particles is still underpredicted by both correction schemes in both tests. With the volume averaged flow fields as input, the volume fraction correction gives the best results. However, in the Eulerian-Lagrangian simulations it is demonstrated that the velocity fluctuation model, associated with the velocity correction scheme, is crucial for obtaining accurate predictions of the mean flow fields.

INFLUENCE OF NOZZLE RADIATION ON SOLID ROCKET MOTORS TAIL-OFF THRUST

The aims of this work are focused on the evaluation of the solid rocket motor residual thrust and on the impact of thermal protection properties on such thrust. Indeed, tail-off thrust of solid rocket motors upper stages can last tens of seconds after motor burn-out, affecting the performance of the rocket on sequencing of stage separation. Hence, the knowledge of the tail-off thrust profile is fundamental to properly design wait times and separation systems total impulse of a multi-stage launcher. Therefore, although it has been shown in the past that pyrolysis gases responsible for the residual thrust are mostly produced by alumina molten slag deposited next to the nozzle nose within the combustion chamber, this study is aimed at suggesting that the portion of the nozzle within the combustion chamber can act as the main radiative heat source leading to thermal protection material ablation, and then to residual thrust production. An analysis of an actual solid rocket motor has been performed in the direction of proving the effectiveness of the overall procedure. Then a sensitivity analysis with respect to the quantities identifying the thermal protection properties has been computed in order to evaluate the impact of such variations on the residual thrust profile.