Richard J. Perkins

Hydraulic Models of the Flow Distribution in a Four Branch Open Channel Junction with Supercritical Flow

Intense rainfall on urban areas can generate severe flooding in the city, and if the conditions are right, the flow in the streets can be supercritical. The redistribution of the flow in street intersections determines the flow rates and water levels in the street network. We have investigated the flow that occurs when two supercritical flows collide in a 90° junction formed by streets of identical cross section. Several flow configurations within the intersection are possible, depending on the position of the hydraulic jumps that form in and upstream of the intersection. Previous work has identified three flow types, with Type II flows being further classified into three subregimes. Hydraulic models have been developed, based on the principles of the conservation of flow and momentum flux in the intersection, which predict the angles at which the jumps will form. These models can be used to determine the flow type that will occur. Moreover, additional models have been developed for computing the outflow discharge distribution. For Type I flows, it has not been possible to develop such a hydraulic model for the discharge distribution, but some data are provided for one configuration to indicate the influence of different parameters. For Type II and Type III flows, such models are developed, and their predictions agree with data obtained from the channel intersection facility at the Laboratory of Fluid Mechanics and Acoustics in Lyon.

Numerical study of bubble and particle motion in a turbulent boundary layer using proper orthogonal decomposition

We have studied the motion of bubbles and particles in the near-wall region of a turbulent boundary layer, to investigate the influence of the unsteady turbulent structure. The velocity field was computed using Proper Orthogonal Decomposition (POD), and the trajectories of bubbles and particle have been computed by integrating their equation of motion. We have used this to investigate the roles, and the relative importance, of the different forces acting on bubbles and particles, We find that the unsteady turbulent structure plays an important role in the preferential accumulation of bubbles and particles. The accumulation of bubbles depends on a rather complicated interaction between the pressure gradient and the lift force; neither is sufficient, acting on its own, to explain the strong accumulation observed when they act together.

A New Model for Flow and Dispersion in a Street-Canyon

It is necessary to understand the transport and dispersion of pollutants in city streets, for many reasons. Vehicle emissions form a large proportion of the atmospheric pollutants in urban environments, and these emissions occur within streets, at street level; we need to know how these pollutants are transported between streets, and into the overlying urban canopy. Pollution monitors are usually located within streets, often at street level (see fig. 1), and in order to exploit their measurements fully, we need to understand the relationship between what is measured at a particular location, in very specific circumstances, and the more general state of atmospheric pollution in different areas of the city. Most of the urban population will be exposed to atmospheric pollution within city streets at street level, or within the buildings that border and define the streets. We need to know how this exposure depends on the emissions, the flow and the dispersion within the street.

Transcritical Flows in Three and Four Branch Open-Channel Intersections

AbstractTranscritical flows in three and four branch channel intersections have been studied experimentally, and an empirical relationship is derived from the data to express the flow distribution as a function of the Froude number of the flow in the main channel downstream of the intersection, and in the case of the four-branch intersection, the ratio of the incoming flows in the two inlet channels. The empirical relationship agrees closely with the data from this study, and with data from other studies in comparable conditions. The results illustrate an important point which has been overlooked in some previous studies—the existence of a critical section in the lateral outflow channel is not sufficient to isolate flow in the intersection from the downstream control in the lateral channel. It is shown that if drowned flow occurs in the lateral channel, then the downstream control can affect the flow in the intersection.

Wind Tunnel Study of the Exchange Between a Street Canyon and the External Flow

In the last three decades, in order to model pollutant dispersion inside a street canyon, several models have been proposed to describe mean concentration and retention time of pollutant inside the canyon, in function of the flow dynamics of the external flow (Berkowicz, 2000, Soulhac, 2000, De Paul and Sheih, 1986, Caton et al., 2003). Some of these models take account just of the mean velocity at the roof height Uh, some other do also consider the turbulence intensity of the incoming flow. The aim of this study is to evaluate how different conditions of the external flow induce different velocity field inside the canyon, and to find an appropriate velocity and length scale to characterize the mass exchange between the recirculating region and the external flow.

An experimental investigation of the laminar horseshoe vortex around an emerging obstacle

An emerging long obstacle placed in a boundary layer developing under a free surface generates a complex horseshoe vortex (HSV) system, which is composed of a set of vortices exhibiting a rich variety of dynamics. The present experimental study examines such flow structure and characterizes precisely, using particle image velocimetry (PIV) measurements, the evolution of the HSV geometrical and dynamical properties over a wide range of dimensionless parameters (Reynolds number

Shape oscillations of rising bubbles

Re_{h}\in [750,8300]

Turbulent Transfer Between Street Canyons and the Overlying Atmospheric Boundary Layer

, boundary layer development ratio

Flow Patterns in a Four-Branch Junction with Supercritical Flow

h/\unicode[STIX]{x1D6FF}\in [1.25,4.25]

Closure to “Flow Patterns in a Four-Branch Junction with Supercritical Flow” by Emmanuel Mignot, Nicolas Rivière, Richard Perkins, and André Paquier

and obstacle aspect ratio