FYFD

Tag: Venturi effect

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    How Gas Pump Nozzles Work

    Ever wonder how a gas pump shuts off when the tank is full? You might guess that there’s a sophisticated electronic sensor hidden in there. But there isn’t! Gas pumps use an entirely mechanical technique to sense a full tank and shut off flow, as Steve Mould demonstrates in this video.

    There are two key components — one fluid mechanical and one based on mechanical linkages — inside the handle. The part that senses a full tank is a Venturi tube, shown in Image 2. The top section of the Venturi tube contains a constriction, where (incompressible) flow is forced to speed up. That increase in speed creates a drop in pressure, which is reflected by the movement of the water in the curved tube below the constriction.

    Notice that when there’s no flow through the top tube, the water level is equal on either side of the lower, curved tube. That means that the outside air pressure (connected to the short arm) equals the pressure in the constriction (connected to the long arm). When air is flowing through the constriction, the water level shifts. The water in the short arm gets pushed down while the water in the long arm gets sucked up. That change means that the air pressure outside the tube is now higher than pressure in the constriction.

    I’ll let Steve explain what that means for the gas pump! (Image and video credit: S. Mould)

  • The Shape of Splashes

    The Shape of Splashes

    When a wedge falls into a pool, it creates a distinctive, doubly-curved splash. Here’s how it works. When the front of the wedge first enters the water, it creates a thin sheet of fluid that gets ejected diagonally upward. As the wedge sinks further, the sheet thickens and ejects at a more vertical angle. That creates a low pressure zone in the air beside the splash, which causes outside air to flow inward, generating a sort of Venturi effect under the splash. Because the outer part of the splash sheet is thinner, it’s more strongly affected by the air flow beneath it, and it gets pulled downward, enhancing the splash’s curvature.

    This doubly-curved splash is particular to wedges of the right angle. To see what kind of splashes other shapes make, check out the video below. (Image and video credit: Z. Sakr et al.; for more, see L. Vincent et al.)

  • Venturi Splashes

    Venturi Splashes

    Diving can generate some remarkable splashes. Here researchers explore the splashes from a wedge-shaped impactor. At high speeds, they found that the splash sheet pushed out by the wedge curls back on itself and accelerates sharply downward to “slap” the water surface (top). Studying the air flow around the splash sheet reveals some of the dynamics driving the slap (bottom). The splash sheet quickly develops a kink that grows as the sheet expands. This creates a constriction that accelerates flow on the underside of the sheet. That higher velocity flow means a low pressure inside the constriction, which pulls the thin sheet down rapidly, making it slap the surface. For more, check out the full video. (Image and research credit: T. Xiao et al., source)

  • Windy Urban Corridors (*)

    Windy Urban Corridors (*)

    For pedestrians, windy conditions can be uncomfortable or even downright dangerous. And while you might expect the buildings of an urban environment to protect people from the wind, that’s not always the case. The image above shows a simulation of ground-level wind conditions in Venice on a breezy day. While many areas, shown in blue and green, have lower wind speeds, there are a few areas, shown in red, where wind speeds are well above the day’s average. This enhancement often occurs in areas where buildings constrict airflow and funnel it together. The buildings create a form of the Venturi effect, where narrowing passages cause local pressure to drop, driving an increase in wind speed. Architects and urban designers are increasingly turning to numerical simulations and CFD to study these effects in urban environments and to search for ways to mitigate problems and keep pedestrians safe. (Image credits: CFD analysis – SimScale; pedestrians – Saltysalt, skolnv)

    (*) This post was sponsored by SimScale, the cloud-based simulation platform. SimScale offers a free Community plan for anyone interested in trying CFD, FEA and thermal simulations in their browser. Sign up for a free account here. 

    For information on FYFD’s sponsored post policy, click here.