Ram Accelerator Research Articles

Detonation wave structure and thrust variation of a ram accelerator with different projectile velocities

A study was conducted to investigate the effect of velocity on the detonation wave structure and thrust of a ram accelerator using a simulation of a premixed, reacting flow over a conical projectile. The simulation involved solving the compressible reactive Navier-Stokes equations with a detailed chemical model in a channel with a supersonic stoichiometric hydrogen-oxygen inflow. Results showed that at projectile velocities lower than the Chapman-Jouguet detonation velocity, a thermally choked unstart occurs. As the projectile velocity increases, the overdriven detonation mode, trans-detonative mode, and super-detonative mode successively form. The maximum thrust was achieved at the lower velocity limit under the overdriven normal detonation condition, but decreased continuously as an oblique detonation wave formed. The super-detonative mode was distinguished by the smoothness of the tail thrust derived from the recirculation zone and ignition before the conical ramp led to an unstart at the upper velocity limit.

Numerical Investigation of the Oblique Detonation Waves and Stability in a Super-Detonative Ram Accelerator

This study numerically investigates the effects of diluent gas proportion, the overdrive factor, and throat width on the wave structure and thrust performance of a ram accelerator operating in super-detonative mode. For premixed gas of a high energy density, a typical unstart oblique detonation wave system is observed due to the ignition on the front wedge of the projectile, and the detonation waves move downstream to the shoulder as the energy density decreases. In the start range of the overdrive factor, the wave position also shows a tendency to move downstream as the projectile velocity increases, accompanied by oscillations of the wave surface and thrust. As the throat width increases, the wave standing position changes non-monotonously, with an interval of upstream movement and Mach reflection. The typical wave structure of a ram accelerator in super-detonative mode is identified, as well as the unstart stable wave features and the unstable process for choking, which can provide theoretical guidance for avoiding unstart issues in ram accelerators and optimizing their performance.

Investigation of the Flow In Cold Condition at the Exit of a Supersonic Combustor Test Bench

For studies of hypersonic flows and supersonic combustion in ground test facilities, three devices can be used as ram accelerators, shock tunnels and supersonic combustor test benches. These devices can reproduce, on the ground, similar conditions to those in real flight at a certain altitude and speed. In the case of the supersonic combustor test bench (SCTB), it simulates the same flow conditions inside the combustor of a scramjet. The SCTB consists basically of a combustion chamber or vitiated air generator unit, where the air is heated, and a nozzle, where the air is accelerated to the desired test speed. The supersonic combustor to be tested is directly coupled to the nozzle exit of the SCTB. Ultimately, it was necessary to use a transition piece to connect the nozzle to the combustor to be tested, because the nozzle exit has a circular section and the combustor entrance has a rectangular one. This work aims to present the process of characterizing the cold flow along the SCTB of the Institute for Advanced Studies (IEAv) using the schlieren technique. The interference of the transition piece in obtaining the required flow conditions at the exit of the SCTB or the entrance of the combustor was mainly evaluated.

Influence of Taylor waves on standing windows of oblique detonation wave

An oblique detonation wave stabilized over a body has been studied due to the ongoing development of high-speed propulsion systems, such as oblique detonation wave engines and ram accelerators. Standing window of oblique detonation wave reflects the degree of standing difficulty. Firstly, Shock relations coupled with chemical equilibrium are solved to draw detonation polar diagrams between oblique detonation angle and wedge angle by iterative algorithm. In these diagrams, the wedge angle detaching from the wedge nose is referred as the maximum wedge angle θιηॉκ and forming CJ detonation in the direction normal to the oblique detonation wave is referred as the minimum wedge angle θख़τ. The region between the two wedge angles is regarded as the standing windows. G. Emanuel holds that Taylor waves follow the oblique detonation wave as the wedge angle is smaller than θख़τ. Based on reactive Euler equation, wedge-induced oblique detonation is simulated in this paper. For the case of the wedge angle below θख़τ, Taylor waves change post-detonation wave flow field to maintain standing oblique detonation wave. Therefore, the standing window becomes wider.

Hybrid Spin-CMOS Polymorphic Logic Gate With Application in In-Memory Computing

In this article, we initially present a hybrid spin-CMOS polymorphic logic gate (HPLG) using a novel 5-terminal magnetic domain wall motion device. The proposed HPLG is able to perform a full set of 1and 2-input Boolean logic functions (i.e., NOT, AND/NAND, OR/NOR, and XOR/XNOR) by configuring the applied keys. We further show that our proposed HPLG could become a promising hardware security primitive to address IC counterfeiting or reverse engineering by logic locking and polymorphic transformation. The experimental results on a set of ISCAS-89, ITC-99, and Ecole Polytechnique Federale de Lausanne (EPFL) benchmarks show that HPLG obtains up to 51.4% and 10% average performance improvements on the power-delay product (PDP) compared with recent non-volatile logic and CMOS-based designs, respectively. We then leverage this gate to realize a novel processing-in-memory architecture (HPLG-PIM) for highly flexible, efficient, and secure logic computation. Instead of integrating complex logic units in cost-sensitive memory, this architecture exploits a hardware-friendly approach to implement the complex logic functions between multiple operands combining a reconfigurable sense amplifier and an HPLG unit to reduce the latency and the power-hungry data movement further. The device-to-architecture co-simulation results for widely used graph processing tasks running on three social network data sets indicate roughly 3.6× higher energy efficiency and 5.3× speedup over recent resistive RAM (ReRAM) accelerators. In addition, an HPLG-PIM achieves ~4× higher energy efficiency and 5.1× speedup over recent processing-in-DRAM acceleration methods.

Unsteady 1-D Thrust Modeling with EOS Effects for Ram Accelerator Experiments at Different Bores

Advances made to the unsteady, one-dimensional (1-D) modeling of the thermally choked ram accelerator thrust-Mach number characteristics include the use of real-gas equations of state to account for the compressibility effects of the combustion products. Equations of state based on generalized empirical and theoretical considerations are incorporated into a 1-D computer code to predict the combustion end state equilibrium conditions when the propellant starts out a relatively high fill pressure (>2.5 MPa) and the projectile acceleration exceeds 100 km/s2. The objective of this work is to improve the unsteady 1-D model as a useful tool to predict the thrust of the thermally choked ram accelerator propulsive mode by utilizing key results from the more computationally intensive 2-D or 3-D simulations. New thrust-Mach number calculations compared with experimental data from 25-mm, 30-mm, 38-mm, 90-mm, and 120-mm-bore experiments are generally in good agreement until the point where enhanced accelerations are observed, presumably due to projectile material combustion. The results of this investigation indicate the need for more research on ram accelerator flow fields and the role projectile material may play in the combustion process.

Numerical investigation of the acceleration performance of a thermally choked ram accelerator

The flow fields of the thermally choked mode of ram accelerators were studied numerically. The goal of this study was to investigate the effects of the gas reaction rate, the velocity and the projectile shapes on the performances of ram accelerators. The thermally choked mode was demonstrated to occur only when the variations in the reaction rate and projectile velocity were within certain limits. The use of a boat-shaped projectile can extend this limit. The flame front can stand at both its shoulder and the base, and the thrust is the greatest at its shoulder.

Equations of state implementation for 1-D modelling of performance in ram accelerator thermally choked propulsion mode

This paper presents advancement on one–dimensional (1–D) unsteady modelling of a ram accelerator (RAMAC) in the sub–detonative velocity regime by including real–gas equations of state (EoS) in order to account for the compressibility effects of the combustion products. Several equations of state based on generalised empirical and theoretical considerations are incorporated into a 1–D computer code TARAM. The objective of this work is to provide the best available formulations in order to improve the unsteady 1–D model and make the TARAM code a useful tool to predict the performance of the RAMAC in the sub–detonative velocity regime, without having to resort to more complicated 2–D or 3–D computational schemes. The calculations are validated against experimental data from 38–mm and 90–mm–bore facilities and good agreements have been achieved. Yet, the results demonstrate the need for further CFD studies involving the scale effect.

초폭굉 모드 램가속기의 성능해석에 대한 이론적 연구

An analytical study on performance evaluation of superdetonative mode ram accelerator was conducted for understanding the experimental result. The quasi-one dimensional continuum, momentum, energy equations were solved under the assumption of inviscid flow. It would be noticeable that experimental result could be analytically simulated with the assumptions of inlet shockwave, temperature dependent specific heat, and additional aluminum combustion due to ablation of aluminum projectile in superdetonative operation mode. The acceleration of ram accelerator was comparable to experimental result with the consideration of the additional aluminum combustion energy by ablation of projectile. As result, the experimental result with the aluminum projectile could be affected by heat of aluminum.

Experimental Investigation of Transient Flow Measurement in the Ram-Accelerator High Pressure Pneumatic System

A high-pressure-pneumatic mass flow control test-bed using inert medium was built in order to study the transient flow characteristic of high pressure gas feed system in ram accelerator. The structure of a new type measurement system of transient flow characteristic experiments applied to the test-bed was introduced as also. Measurement tests that high pressure gas-flow ejecting into a tank with exhaust-back-pressure through a high pressure fueling valve were conducted to ascertain the transient discharge coefficient. The results suggest that: The transient discharge coefficient increases with the inlet pressure difference of high pressure fueling valve according to polynomial law. Correlations between inlet pressure difference and transient discharge coefficient was obtained based on the experimental data. The correlation coefficient between the least square fitting curve of the correlations and experimental results reaches 0.994.The system could be used to study the change regularity of pressure and time in the fueling process of high pressure gas.

Detonative propulsion

A survey of propulsion based on detonation of chemical systems is provided in this paper. After a short historical review, basic schematics of engines utilizing detonation as the combustion mechanism are described. Possible improvement of propulsive efficiency due to detonative combustion which results in a significant pressure increase is presented, and a comparison of deflagrative and detonative combustion is discussed. Basic research on Pulsed Detonation Engines (PDE) and rotating detonations in cylindrical and disk-like chambers for different mixtures is presented. Basic principles of engines utilizing Standing Detonation Waves as well as Ram Accelerators are also provided. Detailed descriptions of PDE as well as Rotating Detonation Engines (RDE) are given. Different implementations of the PDE concept are presented and experimental and theoretical results to date are reviewed. Special attention is given to RDE, since rotating detonation can be applied to all kinds of propulsive engines including rocket, ramjet, turbine, and combined-cycle engines. A survey of detonative propulsion research carried out at different laboratories is presented, and possible future applications of such propulsion systems are discussed. A short note on detonative propulsion using non-chemical energy sources is also given.

Convergence issues in using high‐resolution schemes and lower–upper symmetric Gauss–Seidel method for steady shock‐induced combustion problems

SUMMARYThis paper reports numerical convergence study for simulations of steady shock‐induced combustion problems with high‐resolution shock‐capturing schemes. Five typical schemes are used: the Roe flux‐based monotone upstream‐centered scheme for conservation laws (MUSCL) and weighted essentially non‐oscillatory (WENO) schemes, the Lax–Friedrichs splitting‐based non‐oscillatory no‐free parameter dissipative (NND) and WENO schemes, and the Harten–Yee upwind total variation diminishing (TVD) scheme. These schemes are implemented with the finite volume discretization on structured quadrilateral meshes in dimension‐by‐dimension way and the lower–upper symmetric Gauss–Seidel (LU–SGS) relaxation method for solving the axisymmetric multispecies reactive Navier–Stokes equations. Comparison of iterative convergence between different schemes has been made using supersonic combustion flows around a spherical projectile with Mach numbers M = 3.55 and 6.46 and a ram accelerator with M = 6.7. These test cases were regarded as steady combustion problems in literature. Calculations on gradually refined meshes show that the second‐order NND, MUSCL, and TVD schemes can converge well to steady states from coarse through fine meshes for M = 3.55 case in which shock and combustion fronts are separate, whereas the (nominally) fifth‐order WENO schemes can only converge to some residual level. More interestingly, the numerical results show that all the schemes do not converge to steady‐state solutions for M = 6.46 in the spherical projectile and M = 6.7 in the ram accelerator cases on fine meshes although they all converge on coarser meshes or on fine meshes without chemical reactions. The result is based on the particular preconditioner of LU–SGS scheme. Possible reasons for the nonconvergence in reactive flow simulation are discussed.Copyright © 2012 John Wiley & Sons, Ltd.

Improved One-Dimensional Unsteady Modeling of Thermally Choked Ram Accelerator in Subdetonative Velocity Regime

The subdetonative propulsion mode using thermal choking has been studied with a one-dimensional (1D) real gas model that included projectile acceleration. Numerical results from a control volume analysis that accounted for unsteady flow effects established that the thrust coefficient versus Mach number profile was lower than that obtained with a quasi-steady model. This deviation correlates with experimental results obtained in a 38-mm-bore ram accelerator at 5.15 MPa fill pressure. Theoretical calculations were initially carried out with the assumption that the combustion process thermally choked the flow about one projectile length behind the projectile base. Thus the control volume length used in this 1D modeling was twice the projectile length, which is consistent with experimental observations at velocities corresponding to Mach number less than 3.5. Yet the choice of the length of the combustion zone and thus the control volume length remains a key issue in the unsteady modeling of the ram accelerator. The present paper provides a refinement of the unsteady one-dimensional model in which the effect of control volume length on the thrust coefficient and the projectile acceleration were investigated. For this purpose the control volume length determined from computational fluid dynamics (CFD) as a function of projectile Mach number was applied. The CFD modeling utilized the Reynolds-averaged Navier-Stokes (RANS) equations to numerically simulate the reacting flow in the ram accelerator. The shear-stress transport turbulence and the eddy dissipation combustion models were used along with a detailed chemical kinetic mechanism with six species and five-step reactions to account for the influence of turbulence and rate of heat release on the length of the combustion zone. These CFD computational results provided Mach number dependent estimates for the control volume length that were implemented in the 1D modeling. Results from the proposed improved 1D unsteady modeling were compared and validated with ram accelerator experimental data with significant improvements in terms of the predicted thrust dependence on Mach number.

Numerical study of gaseous reactive flow over a ram accelerator projectile in subdetonative velocity regime

Computational fluid dynamics solutions of the Reynolds Averaged Navier-Stokes equations have been used to numerically predict the thrust of a thermally choked ram accelerator in subdetonative velocity regime. Studies were focused on a projectile operating in a 38-mm-diameter ram accelerator tube loaded with premixed propellant gas; methane/oxygen/nitrogen at 5.15 MPa fill pressure. Simulations were carried out for a series of incoming velocities. The shear stress transport turbulence model (SST) and the eddy dissipation combustion model (EDM) with five-step reaction mechanism were used to simulate the fully turbulent reactive flow field around the projectile. The predicted projectile thrust-velocity agreed well with the experimental measurements, in addition, the CFD predicted pressure variation and magnitude along projectile axial direction also agreed well with the test data. The present investigation reveals some key features of the shock-wave system around the projectile, which are important in determining the characteristics of the thermally choked propulsive mode. These findings are useful in understanding the characteristics of high speed turbulent combustion process in the ram accelerator.

Equations of state for 1-D modelling of ram accelerator thrust in thermally choked propulsion mode

A one-dimentional performance analysis code has been developed at eh Laboratoire de Combustion et de Detonique to predict the thrust in the thermally choked ram accelerator propulsion mode. This code includes the real gas effect in steady calculations and incorporates the following equations of state: ideal gas, Boltzman, Percus-Yevick (PY) and Becker-Kistiakowsky-Wilson (BKW). The code was validated against key experimental data from representative experiments at the University of Washngton 38-mm-bore facility. The predicted thrust and valicity agree well with experimental measurements. The present paper provides details about the algorithm of the calculation in the thermally choked propulsion mode.

Ram Accelerators: Outstanding Issues and New Directions

An assessment of the key issues affecting the thrust and maximum velocities that can be obtained in ram accelerators is presented. The regimes of ram accelerator operation (subdetonative and superdetonative) are discussed, and simple models for thrust are compared to experimental results and found to be satisfactory. The phenomena that are responsible for the operating limits of these modes of operation are explored, and potential solutions for overcoming these limits are discussed. In particular, the possibility that flow separation may cause unstarts in both the subdetonative and superdetonative ram accelerator is shown to explain qualitatively the experimentally observed limits. A potential remedy to the unstart problem that involves modifying the geometry of the ram accelerator tube is presented. The role of the projectile material, which may react with the oxidizing environment of the propellant, also has a significant effect on superdetonative operation. Techniques to address this problem are outlined. Other novel concepts, such as the use of an explosive-lined launch tube and the laser-driven ram accelerator, are discussed as well.

4716 デトネーションのエンジンシステムへの応用(S56-3 エンジン燃焼-さらなる進化を目指して-(3),S56 エンジン燃焼-さらなる進化を目指して-)

This paper describes one of new concepts on application of detonation waves to the engine systems. The detonation wave is a combustion wave which propagates with a supersonic speed and a steep pressure rise. In normal engine systems, such as the spark ignition engine and the gas turbine, the detonation phenomena should not occurred because their steep pressure rise. But, in principle, the detonation can short a combustion time to a minimum. The decrease of the combustion time increases a thermal efficiency. Examples which are developed as detonation engines are a Scram-Jet engine, a Ram Accelerator and a Pulse Detonation Engine (PDE). The present article describes the PDE which are developed recently, and which utilizes the propagating detonation wave through a chamber.

Mixture Optimization of Superdetonative Ram Accelerator Using Refined Response Surface Method

Mixture Optimization of Superdetonative Ram Accelerator Using Refined Response Surface Method

Modeling Acceleration Effects on Ram Accelerator Thrust at High Pressure

A = tube section a = acceleration cp = isobaric heat capacity F = thrust h = specific enthalpy I = nondimensional thrust, F/(p A) L = length M = Mach number m = mass P = pressure ratio p = pressure Q = nondimensional heat release, q/cpT R = gas constant T = temperature u = velocity v = specific volume α = intermediate calculation parameter, LCVap = adiabatic specific heat capacity ratio γ = specific heat capacity ratio q = heat release η = calorific imperfection, h/cpT σ = compressibility factor

WS3-3 ラム加速器によるCJデトネーション速度付近での衝撃波-燃焼の可視化実験(WS3 衝撃波/燃焼を伴う流れ,ワークショップ)

WS3-3 ラム加速器によるCJデトネーション速度付近での衝撃波-燃焼の可視化実験(WS3 衝撃波/燃焼を伴う流れ,ワークショップ)