Browsing by Issue Date, starting with "2022-05-15"
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- On The Stratification Of Density At Supercritical Liquid-Like ConditionsPublication . Magalhães, Leandro; Silva, A. R. R.; Barata, Jorge M MEfficiency optimization of power systems such as diesel and liquid propelled rocket engines leads to mixture behavior to enter transcritical and supercritical regimes, where distinct coupling mechanisms from those at subcritical conditions govern the thermophysical processes. In the present manuscript, we numerically evaluate the effect of pseudo-boiling at supercritical liquid- and gas-like conditions (reminiscent to liquid and gas phases) and compare the results against experimental nitrogen injection data, which serves as a surrogate for the oxygen-hydrogen propellant combination encountered in most liquid rocket engines. Thus, we can evaluate supercritical fluid behavior using nitrogen without including combustion and finite-rate kinetics into the computational model. We can show the occurrence of density stratification at both liquid- and gas-like conditions, directly connected to the event of the pseudo-phase change inside the injector, meaning that in certain situations, we can have the same fluid behavior for both pseudo-phases. However, density stratification at liquid-like conditions has not been demonstrated in the literature. Therefore, it is an argument in favor of the importance of injector heat transfer in the computational modeling of such flows.
- Numerical Modeling Of Freezing Water DropletsPublication . Magalhães, Leandro; Meireles, Rúben D. S. O.; Silva, A. R. R.; Barata, Jorge M MThis work enhances the understanding of droplet dynamics under cryogenics conditions through an in-house developed analytical tool used to predict the supercooling of water droplets. The physical process is based on a full-scale four-stage supercooling process in which the recalescence stage is assumed instantaneous and the crystallization kinematics of the droplet neglected. The transition temperature of each stage is obtained, resorting to a theoretical balance for the droplets internal energy against the heat loss to the environment. In this way, the representation for the droplets temperature curves alongside the time. The droplets are considered spherical, and the internal motion is so vigorous that complete mixing occurs. The droplets convective effects are accounted for using the Ranz-Marshall classical formulation.
- The Influence Of Liquid Film Thickness On Crown Development: Crown Sheet AnglePublication . Ribeiro, Daniela; Barata, Jorge M M; Silva, A. R. R.Droplet impact upon a liquid film is a phenomenon widely observed in nature but also extensively reported in the literature for a variety of different applications [5]. Fuel injection in internal combustion engines is one of the many applications of studying this type of impact. Among all possible outcomes of a single droplet impinging on a liquid wall, crown splash is one of the most studied phenomena. Yet, it is not completely understood and several researchers seek to understand all physical mechanisms involved and their features. In previous works, [6] focused their work on a specific phenomenon that follows crown splash. Bubble encapsulation happens when the crown liquid sheet bends inwards and eventually the jets on top of the crown merge creating an empty bubble above the horizontal liquid film as shown in Fig. 1. The formation mechanism of this phenomenon is not completely understood, but the crown sheet angle α certainly plays a significant role in its formation. In this way, crown development was investigated for a range of different impact parameters to understand how the crown sheet angle evolves after impact and until the crown collapse.