Numerical study of CFD simulations for compact counter-recoil design of EOD water cannon
Explosive Ordnance Disposal (EOD) robots armed with a water cannon are deployed to disarm the improvised explosive devices. It is critical that the water cannon produces as little recoil force as possible when fired. Otherwise, the robot may be rendered immobile or damaged. In a previous work, a recoilless water cannon was designed through a specific combination of firing experiments and Computational Fluid Dynamics (CFD) simulations. The final design was conceived, prototyped and tested with real bullets. The testing results were found to be satisfactory. In this work, the CFD simulations of the final design was carried out and closely investigated. Numerical study and error analysis were performed in an attempt to find the most suitable and efficient CFD setups for this problem. Two different CFD programs, three different flow domains, and various mesh resolutions were tested.
Compact counter-recoil design of water cannon using a single nozzle with backward spray
A novel design of water cannons using off-the-shelf bullet and barrel was conceptualized, analyzed, prototyped and field-tested. The cannon was designed to be mounted on a remotely controlled carrier robot and its main propose was to utilize water impact to defuse explosives usually placed in metal or wooden containers. In the previous design, the firing created a large recoil force, which was likely to damage and/or immobilize the robot. In the new design presented here, the primary objective was to significantly reduce the recoil force by using backward spray near the muzzle, which allowed the cannon to maintain its destructive power without increasing the robot's payload. In this paper, the design process using a combination of Computational Fluid Dynamics simulations and experiments were presented. The combination was nontrivial but essential due to the limited prior knowledge of the employed bullet (for simulations) as well as firing safety regulation and high prototyping cost (for experiments). The final prototype of the cannon was field-tested and shown to be capable of reducing the recoil force to such an extent that the robot was visibly stationary.
HYPERGOLIC REACTION MECHANISMS OF CATALYTICALLY PROMOTED FUELS WITH ROCKET GRADE HYDROGEN PEROXIDE
Abstract The coupling of the physical and chemical processes controlling the ignition delays (τ ign ) of hypergolic propellants complicates the direct analysis of the transient ignition processes. The transport properties of both the propellants and the ambient gas, and the heat of vaporization and reaction affect τ ign and must be considered experimentally. Furthermore, since hypergolic ignition occurs, by definition, on contact, the mechanics of initial contact and subsequent mixing can affect τ ign and must also be considered. Experimental results from a study of the hypergolic ignition of a catalytically promoted fuel with rocket grade hydrogen peroxide (RGHP) are presented. Statistical analysis of the experimental data was conducted to evaluate the relative effects of RGHP concentration, initial ambient pressure, and the ambient gas on τ ign . At RGHP concentrations of less than 92% in water, stable ignition was difficult to achieve. At sufficiently high Lewis number, an oscillatory ignition process is observed. A phenomenological model comprising mixing, RGHP decomposition, fuel heating and vaporization, and auto-ignition is presented and compared to the experimental results.