A new generation launch vehicle developed by ISRO consists of solid, liquid, and cryogenic stages. Cryogenic stage uses liquid oxygen and liquid hydrogen as oxidizer and fuel, respectively, for propulsion. Fuel and oxidizer are stored in cylindrical tanks with tori-spherical end domes. When the above fluids get depleted from the tanks, dip formation in the liquid surface and subsequent ullage gas entry into the outlet occurs. Formation of surface dip and subsequent gas entry into the outlet is governed by either sink potential phenomenon or vortex phenomenon or combination of both. This could lead to malfunction of the liquid rocket engine. Critical height of propellant from the tank bottom is defined as the elevation at which surface dip forms. Hence, the estimation of critical height is very important in order to quantify unused propellant toward the end of the thrusting phase. Two-phase flow due to vortex can be eliminated by providing either anti-vortex baffle or wire mesh/filter. But it cannot be eliminated due to sink phenomenon unless the outlet is properly designed. Oxidizer tank is provided with a siphoning feed line with wire mesh on the upstream of the inlet to supply contaminant-free liquid oxygen to engine. Published literature on siphoning feed line for the estimation of critical height is very limited. In addition to the above, information on effect of pressure drop due to the presence of wire mesh in the flow path on critical height is also not available. Numerical analysis is carried out using ANSYS CFD software to estimate the critical height for the above siphoning feed line with wire mesh. In order to verify the modeling of wire mesh, two different fluid models (without wire mesh and with wire mesh having zero pressure drop) are used. Oxidizer and gas contained in the tank are idealized as incompressible viscous fluids. Time-dependent Reynolds Averaged Navier Stokes (RANS) equations with continuity and volume fraction equations are solved to estimate the height at which surface dip forms. Numerical simulations are repeated using the fluid model with wire mesh for different pressure drops across it in order to find its effect on critical height. Pressure drop across a wire mesh is due to reduced flow area and is dependent on wire mesh size, density, viscosity, and velocity of fluid. From the numerical investigations, it is found that the presence of wire mesh in the flow path at the upstream of siphoning feed line results in higher critical height due to pressure drop across it. Hence, it is recommended to relocate the wire mesh to the inlet of the siphoning feed line. Another important conclusion is that radial velocity at the inlet of siphoning feed line should be low so that the liquid till its inlet can be utilized. This can be achieved by increasing the bell mouth diameter of the siphoning feed line.

Suresh Mathew Thomas

Papers

Numerical Study of Effect of a Wire Mesh on Fluid Depletion Characteristics of a Cryogenic Propellant Tank