Session ME: General Fluid Dynamics III

Upstream Drafting of a Flexible Body by its Downstream Neighbor

It is common knowledge that an upstream body influences its downstream neighbors in an open flow. This is often referred to as flow drafting or slipstreaming (either in the air or in water). In this talk, we present an experimental study on how the motion of a flapping flag is strongly affected by a downstream neighbor. In a flowing soap film tunnel we introduce, in turn, passive as well as kinematically driven bodies in the wake of an otherwise freely flapping flag. We show how the flapping frequency and drag on the leading flag can be significantly manipulated by the downstream neighbor.   

Cluster formation in traffic models

In this work we study macroscopic traffic models in a lineraly unstable region. It is found that in this case, some clusters appear in the dynamical description. At a first order calculation, an iterative method allows us to construct the Korteweg de Vries equation, which describes a soliton structure. In traffic flow dynamics this fact means that a cluster appears and it travels along the highway with constant speed. The cluster porperties are determined by the experimental information introduced in the model. Some numerical simulations are done to illustrate our results.   

Adaptive Control of the Generalized Korteweg-de Vries Burgers Equation

The adaptive boundary control problem of the generalized Korteweg-de Vries-Burgers (GKdVB) equation when the spatial domain is [0,1] is considered. Three adaptive control laws are designed for the GKdVB equation when either the kinematic viscosity $\nu$ or the dynamic viscosity $\mu$ is unknown, or when both viscosities $\nu$ and $\mu$ are unknowns. Using the Lyapunov theory, the $L^2$-global exponential stability of the solutions of this equation is shown for each of the proposed control laws. Also, numerical simulations based on the Finite Element method (FEM) are given to illustrate the analytical results.   

Effect of orifice eccentricity on the Vortex size downstream orifice cascade in laminar duct flow

Vortex formation and shedding downstream obstructions may be assumed to be one of the main sources of induced vibration and noise in pipes. The vortex size may be estimated from its reattachment length downstream these obstructions. Here, vortex formation downstream orifice cascade in a laminar duct flow has been investigated numerically. The vortex reattachment length downstream the second orifice and the circulation have been studied for different geometry parameters; orifice eccentricity, orifice to duct height ratio and orifice cascade interdistance. The results showed an optimum value (minimum vortex size) is a function of duct geometry and orifice to duct height, a correlation function has been deduced to illustrate this relation. The results showed that the control of these parameters may be of special interest, to reduce the generated vortex size.   

On the increased decay of swirl after vortex breakdown

In this study, vortex breakdown in swirling flows and critical swirl rate for its occurrence was experimentally and numerically investigated. In order to understand and control this interesting phenomenon, a special pipe flow test facility with a rotating honeycomb type swirl generator was constructed. Measurements of all velocity components were carried out by using LDV combined with refractive index matching technique. The maximum Reynolds number and swirl intensity (ratio of angular momentum flux to axial momentum flux) of the flow were Re$_{D}$ = 30,000 and $S_{o}$ = 11, respectively. Measurements at a few diameters downstream of the honeycomb revealed that, beyond a critical swirl intensity setting, the swirl component decayed faster as the swirl intensity was further increased. It is also measured that the axial flow attained reduced or even negative velocities around the centreline after this critical swirl intensity was exceeded. It is argued that rapid decay of swirl component due to vortex breakdown causes the change of tendencies in the flow. Critical swirl intensity was hereby proposed to be $S_{o} \quad \approx $ 0.95, which is important for design and prediction of swirling flows. In order to complement these experimental results CFD analyses were carried out.   

Physical Gelation of a Nano-Composite Soft Glass

Materials in Nature often gain their functionality from being composite on the smallest scale. This is mimicked in manmade nano-composites which profit from the large specific surface area of thin solid enclosures (examples: clay leafs or graphene). Here we use rheology to examine the slow ripening of an out-of-equilibrium model system (``soft glass") that consists of clay particles that swell, break up, and eventually exfoliate into randomly oriented clay leafs through the action of end-functionalized (``sticky") polymer molecules. The nano-composite serves as model soft glass in search of regular patterns in the non-equilibrium dynamics in the approach of equilibrium. Experiments on the model system suggest a scaling relation for the time-resolved viscoelasticity of physical gelation (Macromolecules 43:1901, 2010). Experiments on a wider group of soft glasses is in progress with the objective of confirming or rejecting universality of the novel findings. The experimental protocol includes time-resolved rheometry (Rheol Acta 33:385-397, 1994) and rescaling of data.   

Lonely GPFUTV----the movement of water under the action of an unknown vacuum energy

In this paper, firstly, the experiment on the flow resistance of the aerated pipe flow is introduced. And some experimental research on comparison between different volumes of air entrained is presented. Secondly, the technical characteristics of GPFUTV are dissertated, including creative and functional design, fundamental principle, etc. Under the joint action of an unknown vacuum energy and the formation of non-aerated flow the water flow is full-pipe and continuous, colorless and non-aerated, high-speed and non-rotational as distinguished from laminar flow. Thirdly, an appeal in relation to the experimental research, the applied studies and basic theory research is given. For instance, the well-known Reynolds' experiment under GPFUTV condition, the study of the removal of entrained air in hydraulic fluids, the potential for GPFUTV to be developed for deep seawater suction technology, seawater intake pipe of OTEC and lifting technology for deep ocean mining in Fe-Mn concretions, flow stability and flow resistance under GPFUTV condition, etc.   

Modifying intake flow to increase EGR tolerance in an Internal Combustion Engine

The worldwide effort to reduce vehicle emissions and increase fuel efficiencies has continuously intensified as the need to improve air quality and reduce fuel consumption becomes more acute. Exhaust gas recirculation (EGR) is a method that has long been employed to reduce combustion temperatures and therefore reduce thermal NOx formation and accommodate higher compression ratios and more optimum combustion phasing for improved efficiency. Generally the effective EGR level as a percent of trapped charge is limited by its affect on combustion stability. Inducing flow structures such as swirl, squish and tumble in the trapped charge have proven to extend this EGR limit in homogeneous charge spark-ignited engines at part load, but this enhancement has not been significantly studied at full loads in such engines. This research explored modifying the intake flow into an engine to create tumble and evaluate its effect at high loads in such engines. This exploration included characterizing the flow on a steady flow bench and quantifying the results using engine dynamometer tests.