Fluid

This article presents a preparation methodology for making clear yield pseudoplastic fluids so that repetitive and consistent rheological measurements can be made using two types of Carbopol 980 and Carbopol Ultrez-10. The methodology calls for gentle agitation while dispersing the polymer, leaving it static for 30 minutes for air bubble removal and neutralization while agitating with NaOH followed by 1 hour for the 980 type and 5 hours for the Ultrez-10. Results are presented for the change of rheological parameters with polymer type, polymer concentration, with hydration time, and temperature. Almost all samples exhibited rheological behavior which could be very well described by the Herschel-Bulkley rheological model. Carbopol 980 solutions appear to be very suitable as model clear yield pseudoplastic fluids while Ultrez-10 solutions present some peculiarities rendering them not so suitable as model fluids.

A conceptual framework for analysing the energetics of density-stratified Boussinesq fluid flows is discussed. The concept of gravitational available potential energy is used to formulate an energy budget in which the evolution of the background potential energy, i.e. the minimum potential energy attainable through adiabatic motions, can be explicitly examined. For closed systems, the background potential energy can change only due to diabatic processes. The rate of change of background potential energy is proportional to the molecular diffusivity. Changes in the background potential energy provide a direct measure of the potential energy changes due to irreversible diapycnal mixing. For open systems, background potential energy can also change due to boundary fluxes, which can be explicitly measured. The analysis is particularly appropriate for evaluation of diabatic mixing rates in numerical simulations of turbulent flows. The energetics of a shear driven mixing layer is used to i...

This is a study of the interactions of solitary waves climbing up a circular island. A series of large-scale laboratory experiments with waves of different incident height-to-depth ratios and different crest lengths is described. Detailed two-dimensional run-up height measurements and time histories of surface elevations around the island are presented. A numerical model based on the two-dimensional shallow-water wave equations including runup calculations was developed. Numerical model predictions agreed very well with the laboratory data and the model was used to study wave trapping and the effect of slope. Under certain conditions, enhanced runup and wave trapping on the lee side of the island were observed, suggesting a possible explanation for the devastation reported by field surveys in Babi Island off Flores, Indonesia, and in Okushiri Island, Japan.

Polymer drag reduction, diffusion and degradation in a high-Reynolds-number turbulent boundary layer (TBL) flow were investigated. The TBL developed on a flat plate at free-stream speeds up to 20m s(-1). Measurements were acquired up to 10.7 m downstream of the leading edge, yielding downstream-distance-based Reynolds numbers up to 220 million. The test model surface was hydraulically smooth or fully rough. Flow diagnostics included local skin friction, near-wall polymer concentration, boundary layer sampling and rheological analysis of polymer solution samples. Skin-friction data revealed that the presence of surface roughness can produce a local increase in drag reduction near the injection location (compared with the flow over a smooth surface) because of enhanced mixing. However, the roughness ultimately led to a significant decrease in drag reduction with increasing speed and downstream distance. At the highest speed tested (20m s(-1)) no drag reduction was discernible at the first measurement location (0.56 m downstream of injection), even at the highest polymer injection flux (10 times the flux of fluid in the near-wall region). Increased polymer degradation rates and polymer mixing were shown to be the contributing factors to the loss of drag reduction. Rheological analysis of liquid drawn from the TBL revealed that flow-induced polymer degradation by chain scission was often substantial. The inferred polymer molecular weight was successfully scaled with the local wall shear rate and residence time in the TBL. This scaling revealed an exponential decay that asymptotes to a finite (steady-state) molecular weight. The importance of the residence time to the scaling indicates that while individual polymer chains are stretched and ruptured on a relatively short time scale (similar to 10-3 s), because of the low percentage of individual chains stretched at any instant in time, a relatively long time period (similar to 0.1 s) is required to observe changes in the mean molecular weight. This scaling also indicates that most previous TBL studies would have observed minimal influence from degradation due to insufficient residence times.

In this work, a Drag Reducing Agent (DRA) has been employed to reduce the drag of Iraqi crude oil using Poly Vinyl Pyridine (PVP) at different concentrations (0, 500, 750, 1000, 1250 and 1500 ppm). Results show that a significant decrease in flow index values has been achieved at a concentration range of (750-1500 ppm) in which the lowest value is obtained at a PVP concentration of 1000 ppm. This has been clarified by obtaining flow indexes of less than unity indicating the sample shear thinning. Thus, using a DRA concentration of 1500 ppm for a pipeline decreases the pressure drop by 35.7 % capacity, pipe diameter and length of 0.02 3/s, 0.0508 m and 10 m, respectively. In addition, a maximum drag reduction of 35.1 % has been achieved at the highest concentration (1500 ppm). Therefore, the DRA addition saves the pumping power and increases the produced flow by 35.1 % and 27.5 %, respectively.

The approach of combining computational fluid dynamics (CFD) for continuum fluid and the discrete element method (DEM) for discrete particles has been increasingly used to study the fundamentals of coupled particle–fluid flows. Different CFD–DEM models have been used. However, the origin and the applicability of these models are not clearly understood. In this paper, the origin of different model formulations is discussed first. It shows that, in connection with the continuum approach, three sets of formulations exist in the CFD–DEM approach: an original format set I, and subsequent derivations of set II and set III, respectively, corresponding to the so-called model A and model B in the literature. A comparison and the applicability of the three models are assessed theoretically and then verified from the study of three representative particle–fluid flow systems: fluidization, pneumatic conveying and hydrocyclones. It is demonstrated that sets I and II are essentially the same, wit...

The dielectric constants (relative permittivities) of water, methanol, ethanol, butanol and acetone were measured at 91.3 kPa and (283.15 and 293.15) K and are reported here. The dielectric constants were determined by using a new setup based on a low-pass filter. The obtained dielectric constant values are compared with those reported in the literature, and are consistent with those reported in the literature. The obtained dielectric constant data were also compared with those calculated by the Kirkwood model. The comparisons indicated that Kirkwood model can be successfully used for calculation of dielectric constants of the pure fluids.

The paper investigates the idle operating condition of a current production turbocharged Gasoline Direct Injected (GDI) high performance engine both from an experimental and a numerical perspective. Due to the low engine speed, to the low injection pressure and to the null contribution of the turbocharger, the engine condition is far from the standard points of investigation. According to the low heat flux due to combustion, temperature levels are low and reduced fuel evaporation is expected. Consequently, fuel spray evolution within the combustion chamber and spray/wall interaction are key points for the understanding of the combustion process.
In order to properly investigate and understand the many complex phenomena, a wide set of engine speeds was experimentally investigated and, as far as the understanding of the physics of spray/wall interaction is concerned, many different injection strategies are tested. Among the wide set of experiments, the present paper focuses on a restricted portion which is then numerically reproduced and further investigated.
UV-visible imaging and spectral measurements are carried out in the engine to investigate the spray characteristics and flame propagation. Measurements are performed in the optically accessible combustion chamber realized by modifying the actual engine. The cylinder head is modified in order to allow the visualization of the fuel injection and the combustion process in the fourth cylinder using a high spatial and temporal resolution ICCD detector.
The complete engine cycle is reproduced by means of 3D-CFD simulations using a commercial code; due to the many physical sub-models an ad hoc numerical methodology is validated and implemented. The CFD models are validated against experiments and particular care is devoted to the spray and wall film simulations. A lagrangian approach is implemented in order to simulate the GDI multihole spray. The experimental and numerical comparisons, in terms fuel mixing and flame front propagation, give a good understanding of the idle condition.
CFD analyses prove to be a very useful tool to investigate and understand the effects generated by the direct injection into the combustion chamber and they integrate the information provided by the optical investigations.

Magneto Rheological (MR) fluid is the type of smart fluid whose flow properties can be varied by applying magnetic field which can be used to enhance the properties related to stress. MR fluids are basically non-colloidal suspensions of polarizable particles having a size on the order of a few microns. MR fluids are used in various applications including dampers, brakes, clutches, polishing devices and hydraulic valves and have a very promising potential future; some of them have been used commercially in engineering applications such as automobiles, polishing machines, exercise equipment due to quick response and no effect of temperature. Latest up to date literatures on the applications and challenges in terms of PhD and Master thesis, journal articles, conference proceedings, reports and web materials have been reviewed and reported. This review provides an overview of MR fluids along with its properties, preparation, components and applications.

Turbulent drag reduction by polymer additives in a channel is investigated using direct numerical simulation. The dilute polymer solution is expressed with an Oldroyd-B model that shows a linear elastic behaviour. Simulations are carried out by changing the ...