Branislav Basara

Three phase cavitating flows in high-pressure swirl injectors

The internal combustion engine remains to be one of the most important sources of energy. The direct gasoline injection (DGI) is a new technology that promises considerable improvement of internal combustion engine efficiency. The key component in the DGI engine is its injection system. A three-phase flow simulation of the flow in the high-pressure swirl injector, typical for DGI engines, is presented here. The model is based on the multiphase extension of the two-fluid model. The most important characteristics of the flow were predicted. The results show the formation of a thin conical fuel sheet with an air core. Cavitation was also predicted in the pressure depression initiated in the air core. The presented approach seems to be very promising for the simulation of flows in DGI injectors.

PANS Methodology Applied to Elliptic-Relaxation Based Eddy Viscosity Transport Model

The Partially-Averaged Navier-Stokes (PANS) approach is a recently proposed method which changes seamlessly from the Reynolds-Averaged Navier-Stokes (RANS) model equations to the direct numerical solution (DNS) of the Navier-Stokes equations as the unresolved-to-total ratios of kinetic energy and dissipation are varied. Two variants of the PANS model are derived up to now, one based on the k-e formulation and the other based on the k-ω formulation.We introduce here another variant which is based on four equation eddy viscosity transport model, namely ζ-f turbulence model. Benefits of using such near wall model inside the PANS concept are clearly presented in this paper.

Large Eddy Simulation Investigation of the Hysteresis Effects in the Flow Around an Oscillating Ground Vehicle

This paper presents large eddy simulations (LES) of flow around a simplified vehicle model oscillating around its vertical axis. The frequency of the Strouhal number St = 0.068 and a relatively small amplitude of the oscillation are chosen to be representative for the crosswind conditions of vehicles on the road. The results were found to agree well with data from previous experimental investigations. Furthermore, the differences in LES flows between quasi-steady and dynamic flow conditions are presented and underlying flow mechanisms are explored. The cause of the phenomena of hysteresis and phase shift was found in the inertia of the flow to adjust to sudden changes in the direction of the oscillation of the body.

LES study of breakdown control of A-pillar vortex

Active flow control of the longitudinal vortices that developed near and around simplified A-pillar of a generic vehicle was studied using large eddy simulation (LES). The LES results were validated against existing Particle Image Velocimetry (PIV) and aerodynamic drag data. The LES results were further used to study the flow physics responsible for the development of longitudinal vortices, in particular the vortex breakdown process. Tangential blowing and suction into the shear layer rolling into the longitudinal vortices was found to be a sensitive process that can cause instabilities in the flow. The resulting LES flows also show that actuation influences not only the longitudinal vortex nearest to the actuation slot but also the overall flow. Thus, the influence of the flow control actuation on the entire flow must be considered in order to be able to find the appropriate level of control for optimal aerodynamic performance.

PANS of Rudimentary Landing Gear

The paper presents results of simulations of the flow around rudimentary landing gear using an improved version of the Partially-Averaged Navier Stokes model (PANS z- f). The results are validated against time-averaged flow data such as pressure field and oil-film visualizations as well as quantities such as sound pressure level and surface pressure spectra that are relevant for aero acoustic noise generation. The results of PANS z- f are found to be in good agreement with the experimental data and observations. The PANS z- f presented here shows a clear advantage in the prediction of the flow compared with the reference LES simulation on an identical grid.

Numerical Simulation of the Flow Around a Tall Finite Cylinder Using LES and PANS

Two unsteady numerical techniques, LES and PANS, with difference computer requirements, were used for prediction of the flow around a tall finite cylinder. The well resolved LES was found to predict the flow in agreement with previous experimental observations, while PANS was found to suffer from the combination of k - epsilon model in conjuction with wall function close to the wall of the cylinder and too coarse resolution.

Numerical Investigation of Active Flow Control Around a Generic Truck A-Pillar

Large Eddy Simulations (LES) are conducted to study the actuated flow field around a bluff body. The model is a simplified section of a truck. The aim of the work is to model the separation of the flow acting at the front rounded corners, the so called A-pillars, and to minimize the separation of the flow by means of Zero Net Mass Flux synthetic jets. LES data show the interaction of the flow main structures, the separation mechanism and the effects of the actuation on the flow field. The flow is post processed using modal and frequency decompositions. Relevant results in terms of drag reduction were observed for the actuated flow. The principle flow mechanisms are discussed and an optimal actuation frequency, in terms of induced fluctuations and drag reduction, is identified.

Comparison of Partially Averaged Navier–Stokes and Large-Eddy Simulations of the Flow Around a Cuboid Influenced by Crosswind

The paper presents a partially averaged Navier–Stokes (PANS) simulation of the flow around a cuboid influenced by crosswind. The results of the PANS prediction are validated against experimental data and results of a large-eddy simulation (LES) made using the same numerical conditions as PANS. The PANS shows good agreement with the experimental data. The prediction of PANS was found to be better than that of the LES in flow regions where simulations suffered from poor near-wall resolution.

Numerical Investigation of the Flow Around a Simplified Wheel in a Wheelhouse

The flow around generic wheels in wheel housings used in previous experimental investigations is studied using large eddy simulations (LES). A comparison is given here of the results of the simulations with existing experimental data and previous results of RANS simulations. Both instantaneous and time-averaged flows are described, showing agreement with previous knowledge and adding new insight in flow physics. Two different widths of the wheel housing are used in the simulations, and their influence on the flows is studied. The present work shows that the width of the wheel housing has an influence on flows on both the inside and the outside of the wheelhouse.

LES of the Flow around Ahmed Body with Active Flow Control

Three different activation strategies for active flow control around an Ahmed body are investigated using large eddy simulations. Both the separation region on the slanted surface and the cone-like trailing vortices were influenced using different actuation strategies. However, only one of the flow regions was influenced at a time. The actuation of the separation slant region was done using either constant blowing or periodic blowing and suction through the spanwise slot near the edge between the slant and the top of the body. Another actuation strategy used blowing of constant jets into the cone-like vortices with the objective to weaken them. The latter strategy was found to produce an increased drag in agreement with previous experimental data. Only the actuation strategy using constant blowing along the spanwise slot was found to decrease the overall drag on the body.