International audienceBecause of the extreme complexity of physical phenomena at high pressure, only limited data are available for solver validation at device-relevant conditions such as liquid rocket engines, gas turbines, or diesel engines. In the present study, a two-dimensional direct numerical simulation is used to establish a benchmark for supercritical flow at a high Reynolds number and high-density ratio at conditions typically encountered in liquid rocket engines. Emphasis has been placed on maintaining the flow characteristics of actual systems with simple boundary conditions, grid spacing, and geometry. Results from two different state-of-the-art codes, with markedly different numerical formalisms, are compared using this benchmark. The strong similarity between the two numerical predictions lends confidence to the physical accuracy of the results. The established database can be used for solver benchmarking and model development at conditions relevant to many propulsion and power systems
The design and optimization of liquid-fuel rocket engines is a major scientific and technological challenge. One particularly critical issue is the heating of solid parts that are subjected to extremely high heat fluxes when exposed to the flame. This in turn changes the injector lip temperature, leading to possibly different flame behaviors and a fully coupled system. As the chamber pressure is usually much larger than the critical pressure of the mixture, supercritical flow behaviors add even more complexity to the thermal problem. When simulating such phenomena, these thermodynamic conditions raise both modeling and numerical specific issues. In this paper, both subcritical and supercritical hydrogen/oxygen one-dimensional, laminar flames interacting with solid walls are studied by use of conjugate heat transfer simulations, allowing to evaluate the wall heat flux and temperature, their impact on the flame as well as their sensitivity to high pressure and real gas thermodynamics up to 100 bar where real gas effects are important. At low pressure, results are found in good agreement with previous studies in terms of wall heat flux and quenching distance, and the wall stays close to isothermal. On the contrary, due to important changes of the fluid transport properties and the flame characteristics, the wall experiences significant heating at high pressure condition and the flame behavior is modified.
The heat transfer performances of capillary-driven evaporators are still improving while their pumping capacity remains drastically limited by the porous wick structure. The pump assistance allows this capillary limit to be overcome and more largely, gives the opportunity of an important enhancement of capillary two-phase loops operating range. An experimental device made of a Capillary Pumped Loop coupled with a controlled centrifugal pump located at the inlet of the evaporator was proposed. We have shown that the hybrid system acts as it would in a simple capillary-driven regime with an operating loop pressure drop far beyond the capillary limit (more than 60 kPa i.e. more than 6 times the evaporator capillary limit with methanol) while preserving the evaporator thermal efficiency due to vaporisation. Moreover, we have found that the pump assistance significantly increases the system robustness during large amplitude heat load step and startup by influencing the liquid subcooling and flow rate at the evaporator inlet.
A series hybrid mechanical/CPL system is a way to improve the performance characteristics over a plain CPL system, as demonstrated by Schweickart et al [1]. However, few hybrid loops actually operate because the control of the system remains difficult. An investigation of a controlled hybrid CPL is proposed based on a dynamic model, consisting of the coupling of a CPL model and a mechanical pump whose speed is controlled by a PID. We first theoretically determined the controller parameters versus the CPL characteristics in order to optimize the command for a given CPL. In a second part, some simulations of two different architectures were performed and analyzed. These results have confirmed that the hybrid system is very attractive to greatly improve the CPL performance.
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