Jet Impingement Heat Transfer Characteristics with Variable Extended Jet Holes under Strong Crossflow Conditions

In this paper, detailed flow patterns and heat transfer characteristics of a jet impingement system with extended jet holes are experimentally and numerically studied. The jet holes in the jet plate present an inline array of 16 × 5 rows in the streamwise (i.e., the crossflow direction) and spanwise directions, where the streamwise and spanwise distances between adjacent holes, which are normalized by the jet hole diameter (xn/d and yn/d), are 8 and 5, respectively. The jets impinge onto a smooth target plate with a normalized distance (zn/d) of 3.5 apart from the jet plate. The jet holes are extended by inserting stainless tubes throughout the jet holes and the extended lengths are varied in a range of 1.0d–2.5d, depending on the jet position in the streamwise direction. The experimental data is obtained by using the transient thermochromic liquid crystal (TLC) technique for wide operating jet Reynolds numbers of (1.0 × 104)–(3.0 × 104). The numerical simulations are well-validated using the experimental data and provide further insight into the flow physics within the jet impingement system. Comparisons with a traditional baseline jet impingement scheme show that the extended jet holes generate much higher local heat transfer levels and provide more uniform heat transfer distributions over the target plate, resulting in the highest improvement of approximately 36% in the Nusselt number. Although the extended jet hole configuration requires a higher pumping power to drive the flow through the impingement system, the gain of heat transfer prevails over the penalty of flow losses. At the same pumping power consumption, the extended jet hole design also has more than 10% higher heat transfer than the baseline scheme.

Effect of fragment impact on shaped charge jet formation and penetration into steel target

Purpose This paper aims to investigate the effects of fragment impacts to shaped charge warheads in terms of shaped charge jet formation geometries and penetration performances. Design/methodology/approach In experimental process, a fragment was accelerated to a shaped charge warhead by means of a powder gun to a velocity more than 1,000 m/s, and this impact led to conical damage in the explosive of the warhead. Deformation on the warhead was visualized using X-ray technique to observe holes generated during fragment impact. Penetration test was performed against AISI 1040 steel plates with the damaged shaped charge warhead. Penetration performance of shaped charge jet, which deviated from the symmetry axis, was simulated by using SPEED software with 3-D Eulerian method to validate the numerical modelling method by comparing penetration test and simulation results of damaged warhead. Findings Simulation and test results showed good correlation for the warhead in terms of penetration depth and hole geometry at the impact surface of steel plates. In addition, the effects of the numbers and the geometries of fragment holes on shaped charge jet penetration performances were investigated with validated numerical methods. Simulation results showed that the increase in the number of fragment holes in the explosive of the warhead led to particulation of shaped charge jet that diminished penetration depth in the target plate. Additionally, simulation results also showed that the fragment hole geometry in the explosive after different fragment impact angles affected the amount of jet deviation from the symmetry axis as well as penetration depth in the target plate. Practical implications The results obtained from the current study revealed that fragment impact angle and different number of fragment impact reduced the penetration performance of shaped charge warhead by influencing the symmetry of shaped charge jet negatively. Originality/value The current study fulfils the need to investigate how fragment impact on the shaped charge warhead affect the formation symmetry of shaped charge jet as well as penetration performance by experimental and numerical methods. Penetration performance result of asymmetric jet is compared by experimental and numerical studies. A detailed methodology on numerically modelling of the effect of fragment impact angle and number of fragment impact on shaped charge jet performance is given in this study.

Numerical evaluation of the residual stresses in shot peening of alloy steels

In the present numerical study, the residual stresses generated during the shot peening process were evaluated using the finite element method. The influence of shot velocity on the residual stress distribution due to the indentation of a rigid shot over the target plate of alloy steel was studied. The finite element package ABAQUS 6.20 is used for simulating the shot peening process considering the target plate to be deformable. A parametric study was performed by introducing strain hardening rate as H1 = 800 MPa, keeping the dimension of target plate same with variation in shot velocity 20, 50, 75, 100, 125, and 150 m/s to check the behavior of residual stress distribution. As the indentation takes place over the metallic target plate, elastic-plastic deformation was observed. The indentation of the shot with a different velocity range causes the difference in the depth and size of the dent and induces the compressive residual stress. For perfectly plastic and the strain hardened material, the residual stress contour was simulated. The simulated results for strain hardened material show the significant change in the compressive residual stress in the sub-surface region of the target plate. It is evident from the results that the shot velocity has a significant effect on the residual stress distribution. The maximum compressive residual stress is achieved when the shot is indented at a velocity of 125 m/s.

Numerical Investigation of Penetration Characteristics of Preformed Spherical Fragments at Hyper Velocity

Numerical investigation of penetration characteristics of 6mm SS304 preformed spherical fragments released from a Fragment Generator Warhead (FGW) impacting on Steel 1006 target plate of 1 mm, 3 mm and 6 mm thick in velocity range 1000 m/s to 5000 m/s and impact angle between 0° and 75°, has been carried out using the explicit code LS-Dyna which is predominantly used for solving impact problems. The simulation model employs a strain rate dependent plasticity model viz. Johnson-Cook model supplemented by Gruneisen Equation of State (EoS), to capture the large strain encountered in target plate due to impact of a spherical fragment at high velocities. The simulation model results are presented in terms of crater diameter on the target plate normalised over original fragment diameter. Empirical equations are available in literature to estimate the normalised crater diameter under the same impact conditions employed in simulation models. The simulation model results have been validated with experimental data available in literature and also found to be in good agreement with the results obtained from empirical equations. The effectiveness of the erosion contact algorithm over Smoothed Particle Hydrodynamics (SPH) method in LS-Dyna to reasonably predict the behaviour of the target material at high velocities of impact is demonstrated in the current study.

Effect of Jet-to-Jet Distance and Pipe Position On Flow and Heat Transfer Features of Active Clearance Control Systems

The goal of the present work is to investigate the effect of supply pipe position on the heat transfer features of various active clearance control (ACC) geometries, characterized by different jet-to-jet distances. All geometries present 0.8 mm circular impingement holes arranged in a single row. The jets generated by such holes cool a flat target surface, which is replicated by a metal plate in the experimental setup. Measurements are performed using the steady-state technique, obtained by heating up the target plate thanks to an electrically heated Inconel foil applied on the side of the target opposite to the jets. Temperature is also measured on this side by means of an IR camera. Heat transfer is then evaluated thanks to a custom designed finite difference procedure, capable of solving the inverse conduction problem on the target plate. The effect of pipe positioning is studied in terms of pipe-to-target distance (from 3 to 11 jet diameters) and pipe orientation (i.e. rotation around its axis, from 0° to 40° with respect to target normal direction), while the investigated jet Reynolds numbers range from 6000 to 10000. The obtained results reveal that heat transfer is maximized for a given pipe-to-target distance, dependent on both jet-to-jet distance and target surface extension. Pipe rotation also affects the cooling features in a non-monotonic way, suggesting the existence of different flow regimes related to jet inclination.

Study on Penetration Performance of Rear Shaped Charge Warhead

In guided munitions, the shaped charge jet (SCJ) warhead is located behind the simulation compartment (including the control cabin, the steering gear cabin, and the guidance cabin). Therefore, the order of penetration of the SCJ is the simulation cabin and the target. To study the penetration performance of the SCJ to the target plate, the numerical simulation method is used to study the penetration performance of the designed warhead for the steel target at different standoffs, and the depth of penetration (DOP) at the best standoff is obtained, that is, the DOP of the steel target is about 128 mm. Additionally, the penetration performance of the SCJ warhead to target is studied by numerical simulation and experimental verification. Numerical simulation and experimental results show that the DOP of the SCJ warhead to the steel target is 50 mm without the simulation cabin, and about 30 mm with the simulation cabin. The results show that the penetration performance of SCJ is greatly weakened under the condition of non-optimal standoff, but the rear shaped charge warhead still has a strong penetration performance after completing the penetration of the simulated cabin.

Evaluation of hetro-stacked target plate response toward different nose shaped projectile impact

Detailed experimental and numerical investigations were carried out for evaluating the dynamic response of the stacked target plates toward moderate (100–250 m/s) velocity projectile impact. A single stage gas gun was utilized to launch the hemispherical and the blunt projectile toward two different hetro-stacked configurations (Al-St and St-Al). A comprehensive experimental (high speed 3D-DIC) and numerical (FE) evaluation was conducted to obtain the transient and post-impact behavior of the target plates. Influence of different projectile shapes on the full-field transient deformation profiles of different stacking configurations was studied in detail. Also, typical perforation parameters like plug size, shape, and perforation hole diameters were carefully measured and analyzed. A comprehensive error measure was utilized to quantify the similarity between the experimental and simulation results, a very good agreement was observed.

Numerical Investigation on the Formation and Penetration Behavior of Explosively Formed Projectile (EFP) with Variable Thickness Liner

Explosively formed projectiles (EFPs) are widely used in civil applications and the military field for their excellent impact performance. How to give full play to the energy accumulation effect of explosives and improve the penetration performance has become the main problem of EFP design. The aim of the present study was to investigate the effect of liner structure on EFP formation and its penetration behavior. In order to achieve this, a finite element (FE) model was first established on the basis of the Lagrange and ALE method. Then, formation and penetration performance tests of EFP were performed to verify the validity and feasibility of the proposed FE model, where the configuration, velocity of EFP, and penetration diameter left on the target plate were compared. Finally, by using the proposed FE model, the entire process of the formation and penetration behavior of EFP with axial symmetrical variable thickness liners were analyzed, where spherical-segment liners with uniform and non-uniform thickness were developed. The results were drawn as follows: the numerical simulation error of EFP velocity was less than 5%, and the simulated penetration diameter was compared to the 8.6% error obtained from the experimental method. It demonstrated that the proposed FE model had higher prediction precision. After the explosive was detonated, a forward-folding EFP was formed by the liner with a thin edge thickness, while the EFP formed by the liner with uniform thickness had a backward-folded configuration. It was also found that the liner with a thin edge thickness gave the largest steady velocity of EFP, and it was the lowest by using the liner with uniform thickness. There were two types of loads generated after the formation of an EFP, those were shock wave loading and an EFP, both causing damage in the target plate during the process of an EFP’s penetration into it. The shock wave induced by liners with non-uniform thickness caused higher damage in the target plate, the maximum value of stress was reached at about 4.0 GPa. The forward-folding EFP formed by the liner with the thinnest edge thickness had the largest penetration ability. The backward-folded EFP, owing to the hollow structure, had the worst penetration ability, which failed to penetrate the target plate.