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Ideal Fluids in Motion. Ideal Fluid:. Steady Flow, Incompressible Flow, Non viscous Flow, Irrotational Flow. The Equation of Continuity:.
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Ideal Fluids in Motion • Ideal Fluid: Steady Flow, Incompressible Flow, Non viscous Flow, Irrotational Flow. • The Equation of Continuity: If a fluid is incompressible, its density r is constant throughout. Thus the volume of fluid entering a tube at one end per unit of time must be equal to the volume of fluid leaving the other end per unit time. In the time Dt we have A1v1Dt = A2v2Dt. A1v1 = A2v2 (continuity equation) RV = Av = volume flow rate = constant Rm = rRV = rAv = mass flow rate = constant • Bernoulli’s Equation: Application of W = DKE + DU: F2 = P2A2 M Dx2 = v2Dt F1 = P1A1 M Dx1 = v1Dt PHY 2053
Bernoulli’s Equation: Applications • Bernoulli’s Equation: P + ½rv2 + rgy = constant (conservation of energy for a fluid) • Constant Height (y1 = y2): P + ½rv2 = constant If the speed of a fluid element increases as the element travels along a horizontal streamline, the pressure of the fluid must decrease, and conversely. • Example (velocity of efflux): We can use Bernoulli’s equation to calculate the speed of efflux, v2, from a horizontal orifice (and area A2) located a depth h below the water level of a large talk (with area A1). (1) (1↔2) (2) v1 = v2A2/A1 P1 = P2 = Patm (Torricelli’s Law) PHY 2053
Bernoulli’s Equation: Application • Venturi Meter: A Venturi meter is used to measure the flow of a fluid in a pipe. The meter is constructed between two sections of a pipe, the cross-sectional area A of the entrance and exit of the meter matches the pipe’s cross-sectional area. Between the entrance and exit, the fluid (with density r) flows from the pipe with speed V and then through a narrow “throat” of cross-sectional area a with speed v. A manometer (with fluid of density rM) connects the wider portion of the meter to the narrow portion. What is V in terms of r, rM, h, a, and A? d C (1↔2) (C↔C) PHY 2053
Bernoulli’s Equation: Application • Siphon: The figure shows a siphon, which is a device for removing liquid from a container. Tube ABC must initially be filled, but once this is done, liquid will flow until the liquid surface of the container is level with the tube opening A. With what speed does the liquid emerge from the tube at C? What is the greatest possible height h1 that a siphon can lift water? (S↔A) A = Area of container a = area of tube S y=0 V (A↔C) v (B↔A) v PHY 2053