Solid-Fuel Ramjet Assisted Gun-Launched Projectiles

The principles of construction and operation of a solid-fuel ramjet assisted gun- launched projectile are briefly explained. A concise global-survey of the projects on solid-fuel ramjet powered missiles is presented. Pseudovacuum trajectory is a ballistic trajectory in air of a powered projectile where the thrust always balances the drag. Easy and accurate predictability and insensitiveness to external disturbances are the two major advantages of the pseudovacuum trajectory. This trajectory can be easily achieved for gun-launched projectiles by the use of solid fuel ramjets. A preliminary-sizing procedure for solid fuel ramjet powered gun launched projectile is presented. Supersonic spillage and its momentum, bypass-air momentum, real time variations of stagnation pressure losses at the two rearward steps (one at the inlet to and the other at the exit of the combustion chamber), heat addition losses, and combustion efficiency are included in the procedure. Also, presented are the ramjet-control requirements for a typical 155-mm gun launched projectile. The control requirements are minimal, demonstrating the "self throttling characteristics" of solid fuel ramjets. For the typical 155-mm gun launched projectiles, following pseudovacuum trajectories using solid fuel ramjets, the maximum range is found to be in excess of 40 km

LES Study of Influence of Obstacles on Turbulent Premixed Flames in a Small Scale Vented Chambers

The LES study reported in this paper presents the influence of number and position of the obstacles on turbulent premixed flames. LES simulations have been carried out for a stagnant, stoichiometric propane/air mixture, ignited from rest in a small laboratory scale, vented chamber, capable of rearranging into various configurations based on number and position of baffle plates. The novelty of the present study is two folded. First is the application of novel dynamic flame surface density (DFSD) model to account the sub-grid scale (SGS) chemical reaction rate in LES. Second is the arrangement of these configurations into four families, which facilitate a qualitative comparison with available experimental measurements. The concept of families also offers to understand the flame-flow interactions and the impact of number and position of the baffles with respect to ignition origin

LES study of influence of obstacles on turbulent premixed flames in a small scale vented chamber

The LES study reported in this paper presents the influence of number and position of the obstacles on turbulent premixed flames. LES simulations have been carried out for a stagnant, stoichiometric propane/air mixture, ignited from rest in a small laboratory scale, vented chamber, capable of rearranging into various configurations based on number and position of baffle plates. The novelty of the present study is two folded. First is the application of novel dynamic flame surface density (DFSD) model to account the sub-grid scale (SGS) chemical reaction rate in LES. Second is the arrangement of these configurations into four families, which facilitate a qualitative comparison with available experimental measurements. The concept of families also offers to understand the flame-flow interactions and the impact of number and position of the baffles with respect to ignition origin

Measurements and LES calculations of turbulent premixed flame propagation past repeated obstacles

This article was published in the journal, Combustion and Flame [© The Combustion Institute. Published by Elsevier Inc.] and the definitive version is available at: http://dx.doi.org/10.1016/j.combustflame.2011.05.008Measurements and large eddy simulations (LES) have been carried out for a turbulent premixed flame propagating past solid obstacles in a laboratory scale combustion chamber. The mixture used is a stoichiometric propane/air mixture, ignited from rest. A wide range of flow configurations are studied. The configurations vary in terms of the number and position of the built-in solid obstructions. The main aim of the present study is two folded. First, to validate a newly developed dynamic flame surface density (DFSD) model over a wide range of flow conditions. Second, to provide repeatable measurements of the flow and combustion in a well-controlled combustion chamber. A total of four groups are derived for qualitative and quantitative comparisons between predicted results and experimental measurements. The concept of groups offers better understanding of the flame-flow interactions and the impact of number and position of the solid baffle plates with respect to the ignition source. Results are presented and discussed for the flame structure, position, speed and accelerations at different times after ignitions. The pressure-time histories are also presented together with the regimes of combustion for all flow configurations during the course of flame propagation

LES modelling of explosion propagating flame inside vented chambers with various built-in solid obstructions

This paper presents large eddy simulations (LES) of the transient interaction between propagating turbulent premixed flames and solid obstructions mounted inside a laboratory scale combustion chamber. Interactions between the flame movement and the obstacles found to create both turbulence by vortex shedding and local wake/recirculation whereby the flame is wrapped in on itself, increasing the surface area available for combustion and the rate of local reaction rate. Accounting the influence of such local events in order to predict overall flame spreading speed, flame behaviour and the generated overpressure as a measure of reaction rate are extremely useful in combustion analysis in order to develop new models. The rise in the reaction rate due to the local nature of the flow and the increase in overall pressure due to the enhanced turbulence flame interactions as the flame travels through the unburned fuel air mixture are presented and discussed. The main focus of the current work is to establish the LES technique as a good numerical tool to calculate turbulent premixed propagating flames of propane/air mixture having equivalence ratio of 1.0, which is of practical importance in analysing explosion hazards and gas turbine combustors