A computational study is performed to predict the drag reduction for a base bleed projectile. 2-D and 3-D simulations are conducted to describe the flow past a projectile with base bleed. The calculated computational results are compared with measurements of total drag coefficients based on published results for 155mm K307 projectiles with live/dummy base bleed grain. In addition, the mean drag coefficient measurements based on live firing tests for a five K307 projectiles with live BB grain at different Mach numbers are used to validate results obtained from the computational results. Differences between the drag coefficient calculated from computational and published live firing measurements of the drag coefficient for K307 are less than 5.2% and 6.8% for projectile with dummy and live BB, respectively. On the other hand, the maximum deviation between computational results and real measurements from the live firing tests of live BB projectiles is 2.75%.

Multi-fidelity drag prediction for base bleed projectile

This paper intends to estimate the possible range of a 155 mm artillery shell propelled using a ramjet in a fuel-rich propellant configuration. It also intends to obtain an optimum design of ramjet to maximize the range. A six degree of freedom trajectory simulation was developed to obtain the trajectories of the shell with a ramjet, which dynamically evaluates the off-design performance of the ramjet during the flight. A fuel-rich propellant was taken from literature for evaluating the performance of the ramjet. Various trajectories of shell were obtained at different initial thrusts and A/F ratios and with a constant combustion efficiency of 0.95. Results showed that with a 39-calibre gun, the range enhancement of around 105% compared to the current range of 24 km was obtained with a 155 mm artillery shell without any base bleed unit. This was achieved for the ramjet providing thrust equal to 1.2 times the drag at sea level with an initial A/F ratio of 11.

Trajectory Analysis of a Solid Fuel Ramjet Propelling an Artillery Shell

Evolution characteristics of under-expanded accompanying jet under extreme heat condition

Base bleed, along with boattailing, is widely confirmed to be an efficient technique for drag reduction of projectiles. It is believed that the flow pattern at the projectile base, hence the level of drag reduction, is dependent on the base-bleed exit configuration design. It was also shown that bleeding from annular slots overperformed that from a single central orifice. However, central orifices are required for practical issues and may not be completely eliminated. The effect of simultaneous bleeding from the central orifice and annular slots was not adequately explored before. In addition, the impact of annular slot design on level of drag reduction was not thoroughly clarified in the available open literature. The objective of the present study was to systematically address these two gaps. Following parameterization of the bleed exit configuration, a set of three-dimensional computational simulations are conducted to find the design that yields the maximum drag reduction. A set of live firing experiments are conducted to assess the validity of simulation results. Based on parametric study results, the impact of bleed exit configuration on base flow pattern, base pressure, and total drag coefficient is explained. The optimized bleed configuration was found to yield a further drag reduction up to 5% compared to the baseline configuration, including a single central orifice. 

Computational Parametric Study and Live Firing Validation of Base-Bleed Exit Configuration

Base bleed, in which gases are discharged at the base of projectile, is confirmed to be an effective drag reduction technique. Itis believed that the design of base exit can impact the pattern of gas bleeding and, hence, the level of drag reduction. The present study is aimed to address this dependence that was not clarified in previous studies by examining the reduction in drag acting on a projectile with two different base bleed exit configurations. The first configuration includes a central circular orifice while the other is modified to include a smaller central circular orifice and four annular slots with equivalent total area. Numerical simulations on 3‑D computational domain have been conducted to estimate drag and to explore the base flowfield for each configuration. The computational results at different Mach numbers have been compared with the mean drag based on range shooting for projectiles with both base configurations. In addition, different simulations have been performed to predict the real pattern of bleeding through the modified configuration based on the comparison with firing data at different Mach numbers.

Live Firing and 3D Numerical Investigation of Base Bleed Exit Configuration Impact on Projectile Drag

Numerical simulation of base flow with hot base bleed for two jet models

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Numerical simulation of base flow with hot base bleed for two jet models