Projectile Aerodynamics Overtaking a Shock Wave
01 Nov 2008-Journal of Spacecraft and Rockets (American Institute of Aeronautics and Astronautics (AIAA))-Vol. 45, Iss: 6, pp 1251-1261
TL;DR: In this article, the effects of the projectile overtaking amoving shock wave on the projectile aerodynamic characteristics were analyzed using a moving-grid method to analyze the effect of the collision on the aerodynamic properties.
Abstract: A projectile that passes through a moving shock wave experiences drastic changes in the aerodynamic forces as it moves from a high-pressure region to a low-pressure region. These sudden changes in the forces are attributed to the wave structures produced by the projectile–shock-wave interaction and are responsible for destabilizing the trajectory of the projectile, consequently leading to a loss of projectile stability and control efficiency. A computational study was performed here using a moving-grid method to analyze the effects of the projectile overtaking amoving shock wave on the projectile aerodynamic characteristics. A one-dimensional analysis was also carried out to identify the projectile overtaking criteria. The analytical results show that the projectile overtaking flowfields canbe in a subsonic or supersonicflowregime, based on the relative projectileMachnumber.However, it is found that the actual flowfields in the present computations cannot be distinguishedwith the relative projectileMach number only, because theblast-wave strength is diminishingwith time and space. The aerodynamic characteristics of the projectile are hardly affected by the overtaking process for smaller blast-waveMach numbers, as the blast wave will become weak by the time it is overtaken by the projectile. The projectile drag coefficient is more greatly affected by the unsteady flow structures through which the projectile travels in the near field than by the overtaking process.
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TL;DR: In this article, the wave structure is mainly composed of expansion waves, reflected shock waves and normal shock waves as ETMT moves for enough time at the speed of 1250 km/h.
Abstract: With the increasing demand of faster, safer, and more comfortable rail travel, the evacuated tube maglev train (ETMT) has gradually attracted hot concerns in recent years. According to Kantrowitz limit theory, ETMT may encounter chocked flows, leading to more complex generation and development of a series of waves as ETMT moves rapidly in the tube. To study the wave phenomena produced by ETMT running at the super high-speed, the computational domain geometry model was simplified and then 2-D axisymmetric compressible N-S equation was established in the paper. Dynamic mesh method and dynamic adaptive mesh method were used to simulate the real motion of ETMT and improve the capture accuracy of the waves respectively. Results show that the wave structure is mainly composed of expansion waves, reflected shock waves and normal shock waves as ETMT moves for enough time at the speed of 1250 km/h. The intensity of the normal shock wave in front of the head car experiences four states consisting of rapid increase, initial stability, sudden drop and final stability. In the wake, the flow velocity attenuates in a fluctuating way along the opposite motion direction of ETMT due to the complicated interaction between shock waves and expansion waves.
40 citations
TL;DR: In this article, a computational study using a moving grid method is performed to analyze various fluid dynamic phenomena in the near field of a gun, such as the projectile-shock wave interactions and interactions between the flow structures and the aerodynamic characteristics of the projectile when it passes through various flow interfaces.
Abstract: The aerodynamics of projectiles launched from barrels of various devices is quite complicated due to their interactions with the unsteady flowfield around them. A computational study using a moving grid method is performed here to analyze various fluid dynamic phenomena in the near field of a gun, such as the projectile–shock wave interactions and interactions between the flow structures and the aerodynamic characteristics of the projectile when it passes through various flow interfaces. Cylindrical and conical projectiles have been employed to study such interactions and the fluid dynamics of the flowfields. The aerodynamic characteristics of the projectile are hardly affected by the projectile configuration during the process of the projectile overtaking the primary blast wave for small Mach numbers. However, it is noticed that the projectile configurations do affect the unsteady flow structures before overtaking and hence, the unsteady drag coefficient for the conical projectile shows considerable vari...
12 citations
TL;DR: In this article, a numerical study of the shocked flows generated by a supersonic projectile released from a launch tube into a big chamber has been performed based on fixed Cartesian grids, the two-dimensional axisymmetric Euler equations are solved by the fifth-order WENO scheme implemented with moving boundary conditions.
Abstract: Numerical study of the shocked flows generated by a supersonic projectile released from a launch tube into a big chamber has been performed in this paper. Based on fixed Cartesian grids, the two-dimensional axisymmetric Euler equations are solved by the fifth-order WENO scheme implemented with moving boundary conditions. Both the level set technique and ghost fluid method are used for capturing the moving interface of the projectile implicitly. The numerical results show that complex shock phenomena exist in the transient shock flow, resulting from shock-wave reflection, shock-wave focusing, shock-wave/projectile interaction and shock-wave/contact surface interactions. The relationships between the acceleration of the projectile and the transient shock flow are also discussed in detail.
9 citations
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TL;DR: In this article, a computational study using moving grid method is performed to analyze the effect of the projectile-shock wave interaction, where both cylindrical and conical projectiles have been employed to study such interactions and the fluid dynamics of such flow fields.
Abstract: The aerodynamics of a projectile launched from barrels of various devices is quite complicated due to its interactions with the unsteady flow field around it. A computational study using moving grid method is performed here to analyze the effect of the projectile-shock wave interaction. Cylindrical and conical projectiles have been employed to study such interactions and the fluid dynamics of such flow fields. It is found that the overall effect of projectile overtaking a blast wave on the unsteady aerodynamic characteristics of the projectile is hardly affected by the projectile configurations. However, it is noticed that the projectile configurations do affect the unsteady flow structures and hence the drag coefficient for the conical projectile shows considerable variation from that of the cylindrical projectile. The projectile aerodynamic characteristics, when it interacts with the secondary shock wave, are analyzed in detail. It is also observed that the change in the characteristics of the secondary shock wave during the interaction is different for different projectile configurations. Both inviscid and viscous simulations were done to study the projectile aerodynamics. It is found that the effect of the viscosity on the projectile aerodynamics is negligible but the viscosity does affect the unsteady flow structures around the projectile.
8 citations
TL;DR: In this paper, the authors used time-resolved schlieren and shadowgraph flow visualization techniques to visualize the flow structures associated with a moving projectile in the immediate vicinity of the launch tube (transitional/intermediate ballistic regime).
Abstract: A projectile moving in the transitional/intermediate ballistic regime encounters many complex flow phenomena as the flow field contains two blast waves and several flow interfaces. The aerodynamic characteristics of the projectile are highly influenced by the interaction of the projectile with the surrounding flow field. The present study aims to experimentally visualize the flow structures associated with a moving projectile in the immediate vicinity of the launch tube (transitional/intermediate ballistic regime). In this work, the main focus is to investigate three significant phenomena which normally occur in the transitional ballistic regime and have significant effects on the aerodynamic characteristics of the projectile. These are the moving projectile-standing shock interaction termed as unsteady shock diffraction, shock generation due to the transition in the relative projectile Mach number and the moving projectile-moving shock interaction known as the projectile overtaking phenomenon. Experiments are carried out with projectiles of various configurations for various projectile Mach numbers. The flow field is visualized using time-resolved schlieren and shadowgraph flow visualization techniques. The experiments could capture several interesting features of projectile-flow interactions such as the unsteady shock diffraction, shock generation and overtaking phenomenon in various flow regimes through visualization and quantification of the images using image processing techniques.
4 citations
Cites background or methods from "Projectile Aerodynamics Overtaking ..."
...Rajesh et al. (2008) simulated the projectile overtaking phenomenon taking the blast wave attenuation into consideration, and came to a conclusion that a low primary blast wave Mach number at the time of overtaking will not affect the aerodynamic characteristics of the projectile in a noticeable…...
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...This kind of behaviour is reported in the case of supersonic projectiles with high Mach numbers (Rajesh et al. 2008)....
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...…characteristics of the projectile deviate significantly due to the above-mentioned projectile-flow field interactions as described using the accelerationtime history plot obtained from the numerical simulations of projectiles in the intermediate ballistic regime carried out by Rajesh et al. (2008)....
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...The subsonic overtaking rarely happens as the duration for which the relative projectile Mach number remains to be less than one is small due to the rapid attenuation of the primary blast wave (Rajesh et al. 2008)....
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References
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Book•
01 Jan 1953
TL;DR: In this paper, the Hodograph Method for Two-Dimensional, Subsonic Flow with Small Perturbations is used to describe the dynamics of two-dimensional and three-dimensional flow.
Abstract: Partial table of contents: BACKGROUND. Foundations of Fluid Dynamics. Foundations of Thermodynamics. ONE--DIMENSIONAL FLOW. Isentropic Flow. Normal Shock Waves. Flow in Ducts with Heating or Cooling. INTRODUCTION TO FLOW IN TWO AND THREE DIMENSIONS. The Equations of Motion for Steady, Irrotational Flow. SUBSONIC FLOW. Hodograph Method for Two--Dimensional, Subsonic Flow. Three--Dimensional, Subsonic Flow. SUPERSONIC FLOW. Two--Dimensional, Supersonic Flow with Small Perturbations. Oblique Shocks. Appendices. Index.
2,243 citations
TL;DR: In this paper, the axisymmetric Navier-Stokes equations are solved on a fine grid, and the grid convergence of the drag coefficient is achieved, which is validated by comparing the experimental data of a 80 mm sphere, measured by the accelerometer in a vertical shock tube.
Abstract: The dynamic drag coefficient of a sphere by shock wave loading is investigated numerically and experimentally. The diameter of the sphere is varied from 8 \({\mathrm{\mu}}\)m to 80 mm in numerical simulation. The axisymmetric Navier-Stokes equations are solved on a fine grid, and the grid convergence of the drag coefficient is achieved. The numerical result is validated by comparing the experimental data of a 80 mm sphere, measured by the accelerometer in a vertical shock tube. It is found that the sphere experiences in the early interaction one order higher drag than in the steady state. A transient negative drag, mainly resulting from the focusing of shock wave on the rear side of the sphere, is observed only for high Reynolds number flows, and the drag becomes positive because of increased skin friction for low Reynolds number flows.
113 citations
TL;DR: In this paper, the structure of the flowfields formed about the muzzle of a small caliber rifle during the firing were measured using a time-resolved, spark shadow-graph technique. But the results were limited.
Abstract: The structure of the flowfields formed about the muzzle of a small caliber rifle during the firing are measured using a time-resolved, spark shadow-graph technique. The initial flow from the muzzle occurs as tube gases are forced out ahead of the projectile. The gas is air and the exit properties are Ve =945 m/sec, Me = 1.48 and Pel POO = 15. A second flowfield forms upon separation of the projectile which releases the propellant gases. After an initial, in-bore expansion, the propellant gas muzzle properties are Ve=\29S m/sec, Afe = 1.0, and Pe/Poo =600. While the exit properties are different, the flowfields develop in a similar manner. In the axial or downrange direction, strong coupling between the jet and blast fields is observed; however, along the lateral boundaries, the coupling is very weak with the jet structure remaining invariant once established. Motion of observable discontinuities along the axis of symmetry is shown to qualitatively agree with variable energy blast wave theory. At late times, the air blast and jet flows are shown to uncouple and decay independently.
84 citations
"Projectile Aerodynamics Overtaking ..." refers background or methods in this paper
...Only a few works [9–12] have been made to date to investigate such an interaction flowfield around the flying projectile....
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...So far, the investigation of the projectile aerodynamics and aeroballistics has been limited to the visualization of such flowfields using a high-speed optical system [11], and quantitative data associated with the flying projectile aerodynamics are sparse to date....
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TL;DR: In this paper, a numerical study of the interaction of plane blast waves with a cylinder is presented, which reveals that the blast-wave duration significantly influences the unsteady flow over the cylinder.
Abstract: A numerical study of the interaction of plane blast waves with a cylinder is presented. Computations are carried out for various blast-wave durations and comparisons are obtained with the corresponding results of planar shock-wave. Both inviscid and viscous results based on the solution of the Euler and Navier-Stokes equations are presented. The equations are solved by an adaptive-grid method and a second-order Godunov scheme. The shock wave diffraction over the cylinder is investigated by means of various contour plots, as well as, pressure and skin-friction histories. The study reveals that the blast-wave duration significantly influences the unsteady flow over the cylinder. The differences between the viscous and inviscid results are also discussed.
66 citations
"Projectile Aerodynamics Overtaking ..." refers background in this paper
...Only a few works [9–12] have been made to date to investigate such an interaction flowfield around the flying projectile....
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...It is expected that the aerodynamic forces drastically change as the projectile interacts with the unsteady jet and the shock systems around it, or it passes through the primary blast wave [12]....
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TL;DR: In this article, the performance of seven high-resolution schemes is investigated in various unsteady, inviscid, compressible flows, and the results reveal that the Roe, HLLC and hybrid TVD schemes provide similar and overall the best results.
Abstract: The performance of seven high-resolution schemes is investigated in various unsteady, inviscid, compressible flows. We employ the Roe, HLL (Harten, Lax and van Leer), and HLLC (Toro et al.) Riemann solvers, two variants of the van Leer and Steger–Warming flux vector splitting (FVS) schemes, Rusanov's scheme, and a hybrid total variation diminishing (TVD) scheme that combines a high-order Riemann solver with a flux vector splitting scheme. The above schemes have been implemented in conjunction with an implicit-unfactored method which is based on Newton-type sub-iterations and Gauss–Seidel relaxation. The performance of the schemes has been assessed in six unsteady flow problems: two one-dimensional shock tube problems, shock-wave reflection from a wedge, shock-wave diffraction around a cylinder, blast-wave propagation in an enclosure, and interaction of a shock wave with a gas bubble. More dissipative schemes do not necessarily provide faster convergence per time step and also suppress instabilities that occur in certain unsteady flow problems. The efficiency of the solution depends strongly on the advective (high-resolution) scheme. The results reveal that the Roe, HLLC and hybrid TVD schemes provide similar and overall the best results. For the unsteady problems considered here, the computations show that an explicit implementation based on a TVD, fourth-order Runge–Kutta method results in longer computing times than the implicit-unfactored method.
60 citations
"Projectile Aerodynamics Overtaking ..." refers background in this paper
...This blast wave is usually called the primary blast wave (PBW) and develops with associated starting vortices at the exit of the launch tube [1–3]....
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