Engineering topics

Trinh, H. P.

Publications and source records attributed to Trinh, H. P..

6 records

NASA NTRS2007

Modeling of Turbulence Effect on Liquid Jet Atomization

Recent studies indicate that turbulence behaviors within a liquid jet have considerable effect on the atomization process. Such turbulent flow phenomena are encountered in most practical applications of common liquid spray devices. This research aims to model the effects of turbulence occurring inside a cylindrical liquid jet to its atomization process. The two widely used atomization models Kelvin-Helmholtz (KH) instability of Reitz and the Taylor analogy breakup (TAB) of O'Rourke and Amsden portraying primary liquid jet disintegration and secondary droplet breakup, respectively, are examined. Additional terms are formulated and appropriately implemented into these two models to account for the turbulence effect. Results for the flow conditions examined in this study indicate that the turbulence terms are significant in comparison with other terms in the models. In the primary breakup regime, the turbulent liquid jet tends to break up into large drops while its intact core is slightly shorter than those without turbulence. In contrast, the secondary droplet breakup with the inside liquid turbulence consideration produces smaller drops. Computational results indicate that the proposed models provide predictions that agree reasonably well with available measured data.

Trinh, H. P.↗

NASA NTRS2006

Numerical Modeling of Turbulence Effects within an Evaporating Droplet in Atomizing Sprays

A new approach to account for finite thermal conductivity and turbulence effects within atomizing liquid sprays is presented in this paper. The model is an extension of the T-blob and T-TAB atomization/spray model of Trinh and Chen (2005). This finite conductivity model is based on the two-temperature film theory, where the turbulence characteristics of the droplet are used to estimate the effective thermal diffhsivity within the droplet phase. Both one-way and two-way coupled calculations were performed to investigate the performance of this model. The current evaporation model is incorporated into the T-blob atomization model of Trinh and Chen (2005) and implemented in an existing CFD Eulerian-Lagrangian two-way coupling numerical scheme. Validation studies were carried out by comparing with available evaporating atomization spray experimental data in terms of jet penetration, temperature field, and droplet SMD distribution within the spray. Validation results indicate the superiority of the finite-conductivity model in low speed parallel flow evaporating spray.

Balasubramanyam, M. S.↗

NASA NTRS2006

A New Finite-Conductivity Droplet Evaporation Model Including Liquid Turbulence Effect

A new approach to account for finite thermal conductivity and turbulence effects within atomizing droplets of an evaporating spray is presented in this paper. The model is an extension of the T-blob and T-TAB atomization/spray model of Trinh and Chen [9]. This finite conductivity model is based on the two-temperature film theory in which the turbulence characteristics of the droplet are used to estimate the effective thermal diffusivity for the liquid-side film thickness. Both one-way and two-way coupled calculations were performed to investigate the performance cf this model against the published experimental data.

Balasubramanyam, M. S.↗

NASA NTRS1993

Design study of an advanced gas generator

A gas generator which can be ignited reliably during the initial start-up period and offers fairly uniform gas temperature at the exit was studied numerically. Various sizes and shapes of the mixing enhancement devices and their positions were examined to evaluate the uniformity of the exit gas temperature and the change of internal pressure drop incurred by introducing the mixing enhancement devices. By introducing a turbulence ring and a splash plate with an appropriate size and position, it was possible to obtain fairly uniform gas temperature distributions and a maximum gas temperature that is within the design limit temperature of 1600 R at the generator exit. However, with the geometry studied, the pressure drop across the generator was great, approximately 1150 psi, to satisfy the assigned design limit temperature. If the design limit temperature is increased to 1650 R, the pressure drop across the generator could be lowered by as much as 350 psi.

Kim, S.↗

NASA NTRS1992

Performance effects resulting from plugged liquid oxygen posts of the Space Shuttle Main Engine Injector

The paper discusses the performance effects resulting from plugged LOX posts of the Space Shuttle Main Engine Injector. The simulation was performed with the REFLEQS 2-D code. Analysis was performed axisymmetrically and injector surface was divided into several regions to account for the mixture ratio variation on the injector surface. The reduction of vaccum specific impulse was approximately 0.01 second per plugged LOX post. This reduction is an order of magnitude higher than the result of Space Shuttle flight reconstruction data. It is presumed that this overprediction is due to the axisymmetric simulation that smears local effects.

Kim, S.↗

NASA NTRS1989

Interaction of external conditions with the internal flowfield in liquid rocket engines - A computational study

Computational studies have been conducted to examine the capability of a CFD code by simulating the steady state thrust chamber internal flow. The SSME served as the sample case, and significant parameter profiles are presented and discussed. Performance predictions from TDK, the recommended JANNAF reference computer program, are compared with those from PHOENICS to establish the credibility of its results. The investigation of an overexpanded nozzle flow is particularly addressed since it plays an important role in the area ratio selection of future rocket engines. Experience gained during this uncompleted flow separation study and future steps are outlined.

Trinh, H. P.↗