![]() ![]() If you press the water nozzle on the bottom of the bucket, the nozzle literally sucks itself to the bottom. The Venturi effect can also be experienced when filling a bucket with a water nozzle. Very high flow velocities therefore are present directly behind the ridge. In this case, the house serves as a constriction for the flow, so that the airflow is accelerated as it flows over the house. Paradoxically, the lee side of the building facing away from the wind is usually exposed to greater danger, as the wind speeds are higher and the pressure is lower (greater suction effect). Figure: Blowing off a roof on the lee side by a storm The higher pressure inside the building pushes the roof up, so that the wind gets under the roof and finally rips it off. Inside the building, the air is usually at rest and has a higher pressure. Due to the high wind speeds, the pressure in the surrounding area and thus also above the roof decreases very strongly. This is also a consequence of the decreasing pressure with increasing flow speeds. During extreme storms, entire roofs are often ripped off. The Venturi effect can also be seen in storms. The higher pressure on the door leaf compared to the air pressure in the gap, therefore slams the door with great force, even if the air stream flows with the opening direction of the door! Figure: Slamming a door by the wind Animation: Slamming a door by the wind Ripping off roofs by storms Around the door leaf, the air usually flows at a much lower speed. The air pressure in the gap between the door and the frame drops. The door gap is a constricted cross-section through which the air flows very quickly. The slamming of doors due to a draft, is also due to the Venturi effect. The streamline density is a measure of the velocity of the flow! Figure: Venturi effect for generating lift on aircraft wings Slamming of doors by a draft That the air above the airfoil flows faster than below can be seen graphically by the fact that the streamlines above the wing are closer together. ![]() This principle ultimately produces lift at airfoils, because air upside of the wing flows faster than the air below. Figure: Demonstration of the Venturi effect on a sheet of paper Animation: Demonstration of the Venturi effect on a sheet of paper Due to the fast flowing air on the top side of the sheet, the pressure decreases and the higher pressure on the bottom side (resting air) pushes the sheet of paper upwards. The paper sheet is not pushed down, but lifted up. Now blow with your mouth over the top of the sheet. To do this, hold a sheet of paper at the corners with two fingers and bring it to the lower lip. The decrease in pressure in flowing fluids can be verified relatively easily with a sheet of paper. The present article therefore deals with examples and technical applications of the Venturi effect. In the article Venturi effect, this phenomenon have already been discussed in detail. The Venturi effect ( Bernoulli effect) refers to the decrease in pressure in flowing gases or liquids with increasing flow velocity. ![]()
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