Aishvarya Kumar - Academia.edu (original) (raw)

Uploads

Papers by Aishvarya Kumar

arXiv (Cornell University), Dec 21, 2023

In the present study, RANS-based turbulence models are assessed to simulate the isothermal flow i... more In the present study, RANS-based turbulence models are assessed to simulate the isothermal flow in a combustor representing a constituent can combustor of the can-annular configuration used in jet engines. The models assessed are two equation models: standard k-epsilon, realizable k-epsilon, standard k-omega, SST k-omega and Linear Pressure Strain Reynolds Stress Model. The models were assessed by comparing their predictions of mean axial velocity, mean transverse velocity, turbulent kinetic energy and shear stress to experimental data at two different positions in the combustor: the primary holes plane and the dilution holes plane. The comparison showed that the two-equation models failed to predict the confined swirling flow accurately at both positions. The realizable k-epsilon model was the least accurate, followed by the standard k-epsilon model. The standard K-omega performed slightly better, while the SST K-omega model was the most accurate among the two-equation models. The discrepancies between the predicted and experimental results could be attributed to the isotropic turbulence assumptions which are invalid for confined swirling flows and two-equation models also lack formulations to capture the intricacies of vortex flow and its interaction with the surrounding flows in confined swirling flows. The Linear Pressure Strain RSM model, which considers turbulence anisotropy, showed some promise, although overpredicted, results were in trend with experimental values at the primary holes plane. However, at the dilution holes plane, the model overpredicted the velocity field i.e. mean axial velocity and underestimated the turbulence field including turbulent kinetic energy and shear stress. These observed discrepancies can be ascribed to the pressure-strain correlation in the Linear Pressure Strain RMS model which assumes the pressure-strain correlation is a linear function of the strain-rate tensor. However, for complex flows, this linear assumption is too simplistic. Hence, the results of this study suggest that more advanced turbulence models are needed to accurately predict the confined swirling flow in combustors.

An expert is a person who has made all the mistakes that can be made in a very narrow field

Journal of computational science, Jun 1, 2024

Fluids, 2021

Fluids, 2020

This study assessed two cavitation models for compressible cavitating flows within a single hole ... more This study assessed two cavitation models for compressible cavitating flows within a single hole nozzle. The models evaluated were SS (Schnerr and Sauer) and ZGB (Zwart-Gerber-Belamri) using realizable k-epsilon turbulent model, which was found to be the most appropriate model to use for this flow. The liquid compressibility was modeled using the Tait equation, and the vapor compressibility was modeled using the ideal gas law. Compressible flow simulation results showed that the SS model failed to capture the flow physics with a weak agreement with experimental data, while the ZGB model predicted the flow much better. Modeling vapor compressibility improved the distribution of the cavitating vapor across the nozzle with an increase in vapor volume compared to that of the incompressible assumption, particularly in the core region which resulted in a much better quantitative and qualitative agreement with the experimental data. The results also showed the prediction of a normal shockw...

Fluids

International Journal of Engine Research

This study assesses the predictive capability of the ZGB (Zwart-Gerber-Belamri) cavitation model ... more This study assesses the predictive capability of the ZGB (Zwart-Gerber-Belamri) cavitation model with the RANS (Reynolds Averaged Navier-Stokes), the realizable k-epsilon turbulence model, and compressibility of gas/liquid models for cavitation simulation in a multi-hole fuel injector at different cavitation numbers (CN) for diesel and biodiesel fuels. The prediction results were assessed quantitatively by comparison of predicted velocity profiles with those of measured LDV (Laser Doppler Velocimetry) data. Subsequently, predictions were assessed qualitatively by visual comparison of the predicted void fraction with experimental CCD (Charged Couple Device) recorded images. Both comparisons showed that the model could predict fluid behavior in such a condition with a high level of confidence. Additionally, flow field analysis of numerical results showed the formation of vortices in the injector sac volume. The analysis showed two main types of vortex structures formed. The first kind...

The occurrence of vortices in the sac volume of automotive multi-hole fuel injectors plays an imp... more The occurrence of vortices in the sac volume of automotive multi-hole fuel injectors plays
an important role in the development of vortex cavitation, which directly influences the flow structure
and emerging sprays that, in turn, influence the engine performance and emissions. In this study,
the RANS-based turbulence modelling approach was used to predict the internal flow in a vertical
axis-symmetrical multi-hole (6) diesel fuel injector under non-cavitating conditions. The project
aimed to predict the aforementioned vortical structures accurately at two different needle lifts in
order to form a correct opinion about their occurrence. The accuracy of the simulations was assessed
by comparing the predicted mean axial velocity and RMS velocity of LDV measurements, which
showed good agreement. The flow field analysis predicted a complex, 3D, vortical flow structure
with the presence of different types of vortices in the sac volume and the nozzle hole. Two main
types of vortex were detected: the “hole-to-hole” connecting vortex, and double “counter-rotating”
vortices emerging from the needle wall and entering the injector hole facing it. Different flow patterns
in the rotational direction of the “hole-to-hole” vortices have been observed at the low needle lift
(anticlockwise) and full needle lift (clockwise), due to their different flow passages in the sac, causing
a much higher momentum inflow at the lower lift with its much narrower flow passage.

MDPI Fluids, 2020