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Title: Analysis of Heat Transfer Characteristics of Supercritical Fuels in Rocket Cooling Systems by a Space Marching Numerical Technique
Tutor: Nasuti, Francesco
Keywords: Transcritical propellants
Parabolized Navier Stokes equations
Heat transfer deterioration
LNG used as a coolant in LRE
Low Mach number compressible flows
Issue Date: 12-Mar-2012
Abstract: Methane and Liquefied Natural Gas (LNG) have been recently considered both for launch and for in-space applications because of several advantages they present if compared with other commonly used fuels. In particular, several studies are dedicated at the use of methane in liquid rocket engines with turbopumb fed systems. In this framework, the present study focuses on the use of methane or LNG as coolant in regenerative cooling systems. The study has two main purposes. The first is to understand what are the differences between using pure methane or LNG in a cooling system. The second purpose is to investigate on the heat transfer deterioration which is a thermodynamic phenomenon that could affect methane or LNG in cooling channels. The idea is to fulfill these objectives by numerical studies. The test cases that have to be analyzed are straight channels with circular cross section, a length of the order of the meter and a diameter of the order of the millimeter. The Reynolds number is of the order of 10^5 − 10^6 , which implies that the flow is turbulent. The coolant enters the channels with a supercritical pressure (∼10 MPa) and a subcritical temperature (∼ 110 K), which correspond to a very low compressibility. As a consequence, the inlet Mach number are very low (∼ 0.01). High heat fluxes up to 10 MW/m^2 are enforced along the channel. The temperature variations along the channel cause a change in all the thermophysical properties that strongly nfluence the coolant behavior. Thermophysical properties of real fluids and mixtures of real fluids are used to carry out the present investigations. An equation of state based on the Helmholtz free energy is used for the thermodynamic properties. Transport property models are based on the extended corresponding states approach used in combination with accurate models for the transport properties of each considered species. A numerical code is developed pecifically to deal with the test cases of interest. It is based on parabolized Navier Stokes equations which can be solved with a space marching approach. The numerical model, used together with the selected thermophysical models, is validated against experimental data. Finally the developed code is used to obtain the desired results. First a comparison between LNG and pure methane behavior is carried out which permits to emphasize their different properties. In particular, the influence of the LNG composition on the coolant flow is analyzed. Subsequently, study of the deterioration of the heat transfer is addressed both with methane and LNG. Parametric studies permit to understand what are the main parameters involved in the phenomenon and how it can be handled.
Research interests: LRE cooling system: numerical analysis of supercritical fluids in cooling channels. Numerical study of thermodynamic phenomena that could affect supercritical propellants: heat transfer deterioration. Study of real fluid mixtures, equations of state and transport property models and their application in the study of LNG as a LRE fuel. Study of computational fluid dynamics marching techniques, for the description of low Mach number flows with a high comprimibility. Parabolized Navier Stokes equations.Hybrid rocket engines: numerical simulations of the flow in the combustion chamber.Semi-analytical approaches for the study of high frequency combustion instabilities in LRE.

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