Illustrating the effect of viscoelastic additives on cavitation and turbulence with X-ray imaging

The effect of viscoelastic additives on the topology and dynamics of the two-phase flow arising within an axisymmetric orifice with a flow path constriction along its main axis has been investigated employing high-flux synchrotron radiation. X-ray Phase Contrast Imaging (XPCI) has been conducted to visualise the cavitating flow of different types of diesel fuel within the orifice. An additised blend containing Quaternary Ammonium Salt (QAS) additives with a concentration of 500 ppm has been comparatively examined against a pure (base) diesel compound. A high-flux, 12 keV X-ray beam has been utilised to obtain time resolved radiographs depicting the vapour extent within the orifice from two views (side and top) with reference to its main axis. Different test cases have been examined for both fuel types and for a range of flow conditions characterised by Reynolds number of 35500 and cavitation numbers (CN) lying in the range 3.0–7.7. It has been established that the behaviour of viscoelastic micelles in the regions of shear flow is not consistent depending on the cavitation regimes encountered. Namely, viscoelastic effects enhance vortical (string) cavitation, whereas hinder cloud cavitation. Furthermore, the use of additised fuel has been demonstrated to suppress the level of turbulence within the orifice

Flow in the closure region of partial attached cavitation.

The flow near the closure region of partial attached cavitation was examined using qualitative and quantitative flow visualization techniques. The flows associated with closed and open attached cavitation were examined on nominally two- and three-dimensional test objects. The results of two-dimensional free-streamline theory were compared with the experimentally observed cavity flows. The phase-averaged and unsteady flow fields were examined using Particle Image Velocimetry (PIV). The inception and topology of attached cavitation were related to the non-cavitating flow. The cavities formed on three-dimensional geometries had both open and closed portions, whereas those formed on two-dimensional geometries were always open. The closed cavities on the three-dimensional geometries had laminar reattachment. Open cavities had either laminar or turbulent reattachment. The open cavities with laminar reattachment shed vortical cloud cavitation periodically, whereas open cavities with turbulent reattachment had irregular shedding of vortical structures. Cavity flows with laminar reattachment formed a re-entrant flow. A thin boundary layer on the cavity interface remained attached to the cavity interface. The cavity fared into the solid surface, and the flow was largely irrotational. The profiles of the closed cavities were qualitatively similar to those predicted by two-dimensional free-streamline theory with a re-entrant flow closure. In contrast, cavities that exhibited turbulent flow reattachment had recirculation within the cavity. The turbulent shear flow downstream of the open partial cavity had similar characteristics to those of a non-cavitating shear flow behind a rearward facing step. An adverse pressure gradient abruptly truncated the cavity in the case of the two-dimensional planar geometries. This resulted in the creation of a turbulent liquid shear flow in the wake of the cavity. The collapse of cloud cavitation was shown to introduce significant vorticity and turbulence into the liquid flow downstream of the cavity. The wall-bounded shear flow downstream of cavities with laminar reattachment was very thin with thickness on the order of the non-cavitating boundary layer. Open cavities with a turbulent reattachment produced a turbulent wake with a thickness on the order of the cavity thickness. This was substantially thicker than the non-cavitating boundary layer.Ph.D.Applied SciencesMechanical engineeringMechanicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/131460/2/9909921.pd

VANET- Vehicular Applications and Inter-Networking Technologies

This book provides an invaluable introduction to inter-vehicular communications, demonstrating the networking and communication technologies for reducing fatalities, improving transportation efficiency, and minimising environmental impact. This book addresses the applications and technical aspects of radio-based vehicle-to-vehicle and vehicle-to-infrastructure communication that can be established by short- and medium range communication based on wireless local area network technology (primarily IEEE 802.11). It contains a coherent treatment of the important topics and technologies contributed by leading experts in the field, covering the potential applications for and their requirements on the communications system. The authors cover physical and medium access control layer issues with focus on IEEE 802.11-based systems, and show how many of the applications benefit when information is efficiently disseminated, and the techniques that provide attractive data aggregation (also includes design of the corresponding middleware). The book also considers issues such as IT-security (means and fundamental trade-off between security and privacy), current standardization activities such as IEEE 802.11p, and the IEEE 1609 standard series

A Cluster Analysis Study of Opportune Adoption of Electric Drive Vehicles for Better Greenhouse Gas Reduction

Adoption of electric drive vehicles (EDVs) presents an opportunity for reduction of greenhouse gas (GHG) emissions. From an individual vehicle standpoint however, the GHG reduction can vary significantly depending on the type of driving that the vehicle is used for. This is primarily due to conventional vehicles (CVs) having poor energy efficiency in stop-and-go city-like driving compared to their performance in steady highway-like driving. This study attempts to examine the magnitude of the differential in GHG reduction benefit for real driving behaviors obtained from California Household Travel Survey (CHTS-2013). Recorded vehicles speed traces are analyzed via a fuel economy simulator then a hybrid support vector clustering (SVC) technique is applied to form groups of vehicle samples with similar driving behaviors. Unlike many clustering techniques, SVC does not impose a pre-dictated number of clusters, but has a number of parameters that must be tuned in order to obtain meaningful results. Tuning of the parameters is performed via a multi-objective evolutionary algorithm (SPEA2) after formulating the cluster tuning as a two-objective problem that seeks to maximize: i) differential benefit in GHG reduction, and ii) fraction of the population that groups of vehicles represent. Results show that replacing a CV with its equivalent hybrid (HEV) can reduce GHG emissions per mile of driving by 2 to 2.5 times more for a group of vehicles (best opportune for an EDV) compared to the less opportune group.</jats:p

A Direct Adaptive Controller for ATM ABR Congestion Control

One of the more challenging and yet unresolved issues which is paramount to the success of ATM networks is that of congestion control for Available Bit Rate (ABR) traffic. Unlike other ATM service categories, ABR provides a feedback mechanism, allowing interior nodes to dictate source rates. Previous work has demonstrated how linear control theory can be utilized to create a stable and efficient control system for the purposes of ATM ABR congestion control. This paper extends our previous contribution that assumed a minimum-phase plant, an assumption that is likely violated in practice. Presented here is a direct adaptive controller that uses a finite impulse response (FIR) filter to approximately invert the FIR plant. This controller is well suited for the ATM ABR non-minimum-phase plant. Other control architectures, which motivate the final proposed controller, are also discussed