Annafederica Urbano

Numerical Analysis of Deterioration in Heat Transfer to Near-Critical Rocket Propellants

Liquid propellants, which are typically used for regenerative cooling of rocket thrust chambers, can flow in channels at supercritical pressures and in the neighborhood of pseudocritical temperature (near-critical fluid). This could be for instance the case for the envisioned liquid-oxygen/liquid-methane engines with chamber pressures larger than about 50 bar. When the fluid is in such a near-critical condition, deterioration in heat transfer can occur if the heat transfer level is higher than a threshold value. Aiming to improve flow prediction capabilities for the design of such systems, the present study is devoted to numerical simulations of near-critical fluids flowing in uniformly heated straight tubes. After code validation against experimental data of near-critical-hydrogen flow, numerical simulations of near-critical-methane flow in heated tubes are carried out, each characterized by a different wall heat flux. Results are discussed in detail and the near-critical-methane flow condition that exhibits the heat transfer deterioration is identified and emphasized.

Onset of Heat Transfer Deterioration in Supercritical Methane Flow Channels

The deterioration of forced convection heat transfer can affect channel flows of supercritical fluids and therefore has to be taken into consideration when dealing with regenerative cooling of liquid rocket engines. A threshold value of the ratio between the heat flux and the specific mass flow rate is identified as the main parameter controlling the heat transfer deterioration onset. The threshold parameter depends on the specific thermodynamic conditions of the coolant and in particular on its pressure level. In the present study, a parametric numerical analysis has been carried out on the flow of supercritical methane in heated channels, for an assigned inlet temperature level and varying the inlet pressure. A correlation for the threshold parameter as a function of pressure is then proposed on the basis of the obtained results.

Parametric Analysis of Heat Transfer to Supercritical-Pressure Methane

Methane is an interesting propellant to be used together with oxygen in a liquid rocket engine and has the required features to be used as a coolant in a regenerative cooling system also in the case of an expander cycle engine: in this context its behavior as a coolant ow must be controlled and this is complicated by the fact that methane could be in a near critical condition in the cooling channels and thus be subjected to high thermophysical properties variations. The present study investigates the heat transfer to methane looking at the inuence of the thermodynamic and transport properties variations on the methane heat transfer capabilities. In particular the heat transfer deterioration that could aect methane is deeply investigated. To carry out the necessary parametric studies a parabolized Navier Stokes solver developed by the authors has been used together with accurate equation of state and transport properties models able to describe methane in all the thermodynamic conditions of interest.

Numerical Analysis of Heated Channel Flows by a Space-Marching Finite Volume Technique

7; fully-three-dimensional flow; near-critical thermodynamic conditions of the fluid; fluid decomposition reactions; and coupling between flow and wall temperature evolution. The proposed approximation is to use parabolized Navier–Stokes equations. Parabolization is obtained by neglecting viscous derivatives in the space-marching direction and by considering the streamwise pressure gradient as a source term evaluated on the basis of the overall momentum balance. The algorithm is based on a finite volume approach, which uses a modified Roe’s approximate Riemann solver for a fluid governed by a generic equation of state. Validation of the approach is presented by comparison of the channel-flow results with full Navier–Stokes solutions and experimental data. Results show that the present approach is a practicable one for the study of cooling properties of real fluids in channels.

Parametric Analysis of Cooling Properties of Candidate Expander-Cycle Fuels

Flow evolution and heat transfer capability in the cooling system of liquid rocket engines heavily depend on propellant thermophysical properties. Coolant thermophysical property analysis and modeling is therefore important to study the possibility of relying on a regenerative cooling system, whose performance is crucial to determine feasibility and convenience of pump-fed liquid rocket cycles of the expander type. The aim of the present study is to compare the behavior of different liquid fuels for expander-cycle engines. They are light hydrocarbons, binary mixtures of them, and liquefied natural gas, which is a mixture made basically of methane and minor fractions of other light hydrocarbons and nitrogen. A parametric analysis is carried out by a validated numerical solver to compare temperature increase, pressure loss, and heat transfer evolution for the different fuels along the same straight tube and subjected to assigned heat fluxes. Results show that similar engine performance can be obtained by th...

CFD analysis of hybrid rocket Flowfields including fuel pyrolysis and nozzle erosion

Numerical simulations of the flow in a GOX/HTPB hybrid rocket engine are carried out with a Reynolds averaged Navier-Stokes solver including detailed gas surface interaction modeling based on mass and energy balances. Fuel pyrolysis and heterogeneous reactions at the nozzle wall are modeled via finite-rate Arrhenius kinetics. Global mechanisms are considered for the gas-phase chemistry for the combustion of 1,3-butadiene in oxygen. Results show the role of the gas-phase chemistry modeling and surface boundary condition modeling on the solution. The coupling between the mixing and combustion processes in the flowfield and the thermochemical erosion of a graphite nozzle is finally discussed, showing the effect of the temperature and chemical species distributions in the wall region.

An approximate Riemann solver for real gas parabolized Navier-Stokes equations

Under specific assumptions, parabolized Navier-Stokes equations are a suitable mean to study channel flows. A special case is that of high pressure flow of real gases in cooling channels where large crosswise gradients of thermophysical properties occur. To solve the parabolized Navier-Stokes equations by a space marching approach, the hyperbolicity of the system of governing equations is obtained, even for very low Mach number flow, by recasting equations such that the streamwise pressure gradient is considered as a source term. For this system of equations an approximate Roes Riemann solver is developed as the core of a Godunov type finite volume algorithm. The properties of the approximated Riemann solver, which is a modification of Roes Riemann solver for the parabolized Navier-Stokes equations, are presented and discussed with emphasis given to its original features introduced to handle fluids governed by a generic real gas EoS. Sample solutions are obtained for low Mach number high compressible flows of transcritical methane, heated in straight long channels, to prove the solver ability to describe flows dominated by complex thermodynamic phenomena.

Numerical study of liquefied natural gas as a coolant in liquid rocket engines

Liquefied natural gas is a suitable propellant to be used, together with liquid oxygen as oxidizer, in a liquid rocket engine, because of possible advantages with respect to hydrogen in specific applications. Often approximated as pure methane, liquefied natural gas is a mixture of methane, other heavier hydrocarbons and nitrogen. If is to be used in a regeneratively cooled liquid rocket engine, the knowledge of the thermodynamic and heat transfer characteristics when it flows in the cooling channels is of primary importance. The present study is carried out to understand how the composition can influence the flow in cooling channels. Results show that increasing ethane and propane content in a mixture, the pressure drop decreases but the coolant capability worsens. On the other hand increasing nitrogen content causes both poorer coolant capability and larger pressure drop.