Barbara Betti

Simulation of Gaseous Oxygen/Hydroxyl-Terminated Polybutadiene Hybrid Rocket Flowfields and Comparison with Experiments

Numerical simulations of the flowfield in a gaseous oxygen/hydroxyl-terminated polybutadiene hybrid rocket engine are carried out with a Reynolds-averaged Navier–Stokes solver including detailed gas/surface interaction modeling based on surface mass and energy balances. Fuel pyrolysis is modeled via finite-rate Arrhenius kinetics. A simplified two-step global reaction mechanism is considered for the gas-phase chemistry to model the combustion of 1,3-butadiene in oxygen. Results are compared with the firing test data obtained from a laboratory-scale hybrid rocket in which gaseous oxygen is fed into axisymmetric hydroxyl-terminated polybutadiene cylindrical grains through an axial conical subsonic nozzle. With the oxidizer fed by this injector, which generates nonuniform conditions at the entrance of the fuel port, the fuel regression rate is shown to increase several times with respect to the case of homogeneous injection of the oxidizer through all the grain port area, in agreement with the experimental f...

Numerical Evaluation of Heat Transfer Enhancement in Rocket Thrust Chambers by Wall Ribs

Heat transfer enhancement due to longitudinal wall ribs inserted in a rocket engine thrust chamber is analyzed by means of a Reynolds-Averaged Navier-Stokes equations solver. A ribbed wall experiment is numerically reproduced to assess the capability of the simplified approach to properly capture the heat transfer enhancement. Then, a parametric analysis on the role of the longitudinal rib height on heat transfer enhancement is made on a sample thrust chamber. Results show the expected heat increase related to the surface increase, and highlight the reduction of efficiency for increasing rib height due to the thermal stratification between ribs.

Coupled Heat Transfer Analysis in Regeneratively Cooled Thrust Chambers

The coupled hot gas–wall–coolant environment that occurs in regeneratively cooled liquid rocket engines is studied by a computational procedure able to provide a quick and reliable prediction of thrust chamber wall temperature and heat flux as well as coolant flow characteristics, like pressure drop and temperature gain in the regenerative circuit. The coupled analysis is performed by means of a computational fluid dynamics solver of the Reynolds-averaged Navier–Stokes equations for the hot gas flow and by a simplified quasi-two-dimensional approach, which widely relies on semiempirical relations, for the coolant flow and wall structure heat transfer in the cooling channels. Coupled computations of the space shuttle main engine main combustion chamber are performed and compared with available literature data. Results show a reasonable agreement in terms of coolant pressure drop and temperature gain with nominal data, whereas the computed wall temperature peak is closer to hot-firing test data than to the ...

Chemical reaction effects on heat loads of CH4/O2 and H2/O2 rockets

Cooling of liquid rocket thrust chamber walls to allowable solid material temperatures induces near-wall chemical reactions, which are known to have an important role on the heat transfer from the hot gas to the wall. In this study, the contribution of near-wall chemical reactions to heat flux is investigated and quantified by suitable numerical analyses. Numerical results are first compared to literature experimental data of wall heat flux in subscale calorimetric thrust chambers for both oxygen/methane and oxygen/hydrogen propellant combination. Then, a parametric analysis is carried out varying chamber pressure, wall temperature, and propellant combination. This study highlights that oxygen/methane combustion products are more subject to near-wall recombination phenomena. They provide an increase of wall heat flux between 20 and 30% with respect to the frozen flow model evaluation, whereas in the case of oxygen/hydrogen, the wall heat flux increase due to recombination reactions is between 7 and 14%.

Numerical Study of Heat Transfer in Film Cooled Thrust Chambers

Film cooling as a thermal protection for the walls of liquid rocket engines is studied numerically for hydrogen and methane thrust chamber tests. The aim is to verify the capability of the Reynolds Average Navier-Stokes model to capture the basic characteristics of film-cooled thrust chambers, considering a simplified approach, named pseudo-injector approach, which does not model propellant injection and combustion. This assumption allows a great saving in computational time, in particular when considering 3D simulations. The present study takes its origin from the European Community In-Space Propulsion 1 (ISP-1) program where, among various projects, an experimental campaign has been designed to study the film cooling technique in an oxygen/methane thrust chamber and to provide a database for computational fluid dynamics validation. The results show that the present approach gives good results in terms of heat flux characterization, in particular when dealing with test cases of high chamber pressure.

Heat Flux Evaluation in Oxygen/Methane Thrust Chambers by RANS Approach

The demand of a more comprehensive engineering tool for parametric investigations of rocket thrust chambers thermal environment is pushing the improvement of hot-gas side heat transfer prediction tools. In this work, the capability of predicting the heat transfer characteristics of a literature test case for a liquid oxygen / gaseous methane single element combustion chamber is assessed by means of 2D axis-symmetric Reynolds-Averaged NavierStokes simulations. A simplied approach is proposed, where combustion is not simulated, but combustion products enter the chamber through a pseudo-injector. The numerical results show a good agreement with the experimental data, except in the near injection region.

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.

Cooling channel analysis of a LOX/LCH4 rocket engine demonstrator

A computational procedure able to describe the coupled hot-gas/wall/coolant environment that occurs in most liquid rocket engines is presented and demonstrated. The coupled analysis is performed by loose coupling of the two-dimensional axisymmetric ReynoldsAveraged Navier-Stokes equations for the hot-gas flow and the conjugate three-dimensional model for the coolant flow and solid material heat transfer in the regenerative cooling circuit. The latter model is in turn based on the coupled Reynolds-Averaged Navier-Stokes equations for the coolant flow and Fourier equation for the thermal conduction in the solid material. In this study, the thermal behavior of a regeneratively cooled oxygen/methane engine demonstrator is analyzed in detail. Starting from a nominal operative condition of the engine, different levels of channel surface roughness and coolant mass flow rate are considered in order to understand their influence on the heat transfer capability of the cooling system. Results show that the heat transfer can be markedly impaired if the operating parameters undergo rather minor changes with respect to the nominal condition.

Numerical Simulation of Hot-Gas Side Heat Transfer Enhancement in Thrust Chambers by Wall Ribs

uxes. Heat transfer accurate prediction is one of the key features for the development of these engines, especially in the case of expander cycle feed system. In the present study, hot-gas side heat transfer enhancement due to ribbed walls in an expander cycle engine thrust chamber is analyzed by means of a Reynolds-Averaged Navier-Stokes (RANS) equations solver. As a validation of the solver, a ribbed wall experimental test case is reproduced to assess the capability of the solver to properly capture thermal boundary layer and heat transfer enhancement. In this test case, heat enhancement is quantied by measuring water coolant temperature increase along the duct. Then a simplied coupling procedure is adopted to compare numerical simulation against experimental data. Finally an expander cycle engine thrust chamber is studied focusing on heat transfer enhancement due to ribbed walls, compared to the smooth wall case. In this study the capability of the solver to be employed as a design tool for wall ribbed thrust chambers is shown. The adequate understanding and accurate prediction of heat transfer characteristics, heat pick-up and wall temperature distribution in the thrust chamber are considered key features for the development of high performance engines, especially in the case of expander cycle. In fact, in these cycles the driving power for the turbo-pumps comes from the fuel used as a coolant in the regenerative cooling circuit. Expander cycle engines are an attractive solution for upper stage and in-space propulsion because of their capability for multiple restarts and throttling. They have the simplest conguration among the pump-fed cycles because

Convective and Radiative Wall Heat Transfer in Liquid Rocket Thrust Chambers

The relative weight of convective and radiative wall heat transfer in liquid rocket engine thrust chambers is estimated by means of dedicated computational fluid dynamics tools. In particular, alth...