Rotational Flow

3 Key excerpts on "Rotational Flow"

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  Handbook of Environmental Fluid Dynamics, Volume One

  Overview and Fundamentals

  • Harindra Joseph Fernando(Author)
  • 2012(Publication Date)
  • CRC Press

    (Publisher)

  389 29.1 Context For. the. present. purposes,. Environmental Fluid Mechanics . (and. the. role. of. rotation. in. environmental. flows). may. be. considered. conveniently.in.terms.of.fluid.motions.and.associated.mass.and. heat.transport.processes.that.occur.in.the.Earth’s.atmosphere.and. hydrosphere.on.local.or.regional.scales . .In.particular,.and.to.dis-tinguish.such.flows.from.those.within.the.larger.(global).domain. covered.by.geophysical.fluid.dynamics.(see,.e .g., .Cushman-Roisin. 2004;.McWilliams.2006;.Vallis.2006),.emphasis.is.placed.on.the. influence. of. the. flows. upon. (and. their. interaction. with). man-made.facilities.and.structures.and.their.responses.to.anthropo-genic.releases.of.mass.and.heat . .Though.the.effects.of.the.Earth’s. rotation. are. known. to. be. important. for. the. global. circulations. of.the.atmosphere.and.oceans.(see,.e .g., .Gill.1982),.smaller-scale. environmental.flows.may.also.be.affected.by.the.presence.of.the. Coriolis. acceleration. associated. with. the. background. rotation. of. the. Earth . . Examples. (Bowden. 1983;. Mann. and. Lazier. 1991;. Rubin. and. Atkinson. 2001). are. (a). tidal. flows. in. coastal. waters,. (b). estuarine. and. river. outflow. plumes,. (c). waves. and. currents. in.large.lakes.and.reservoirs,.(d).boundary.layer.flows.and.sedi-ment. transport. in. coastal. regions,. and. (e). coastal. upwelling,. though.there.are.many.others . .Many.important.global-scale.pro-cesses.(e .g., .the.oceanic.transport.of.pollutants.(Dahlgaard.1995;. Kershaw.and.Baxter.1995)).have.environmental.consequences.on. a.local.scale.(and. vice versa ),.but.they.are.not.included.herein . .For. hydrospheric.flows,.attention.is.limited.to.rotationally-influenced. processes.operating.inshore.of.the.continental.shelf.break.in.the. marine/estuarine.environment.or.within.the.interiors/boundary. layers.of.large.lakes.and.reservoirs.in.the.freshwater.environment . . Rotational. effects. associated. with. atmospheric.

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  Fluid Machinery

  Application, Selection, and Design, Second Edition

  • Terry Wright, Philip Gerhart(Authors)
  • 2009(Publication Date)
  • CRC Press

    (Publisher)

  6.4 Energy (Work) Transfer in a Rotor An expression to evaluate the work done on/by the fluid passing through the moving rotor of a turbomachine can be developed through application of the Reynolds Transport Theorem to the angular momentum principle (Newton’s second law of motion for systems with rotational motion). Recall from earlier study of fluid mechanics that the rate of change of an arbitrary extrinsic prop-erty of a system, B , as the system in question passes through a control volume, can be determined through the relation: d B sys d t = ∂ ∂ t cv ρ b d ∀ + cs b ρ ( C · n ) d A , (6.3) 196 Fluid Machinery: Application, Selection, and Design where b = d B / d m , CV is the control volume, and CS is the control surface. In this and the following equations, the symbol C is used for velocity because Newton’s second law only applies in absolute (i.e., “inertial”) reference frames while in this chapter, the more commonly used V can stand for either absolute or relative velocity. To obtain the form for the angular momentum principle, note that B sys = H = ( r × C ) d m ; b = r × C , and d H d t = M = ( r × F ) . (6.4) Combining Equations 6.3 and 6.4 and using the terms specific to angular momentum, one obtains M = ∂ ∂ t cv ρ ( r × C ) d ∀ + cs ρ ( r × C )( C · n ) d A . (6.5) Now consider the flow through the rotor of an arbitrary turbomachine, as shown in Figure 6.4. The following assumptions and restrictions are made: • Steady flow is assumed ( ∂/∂ t = 0) • There is no “leakage” so that ˙ m out = ˙ m in = ˙ m Rotor Control volume Shaft r 1 r 2 x , axial C q 1 C q 2 C x 1 C x 2 C r1 T o C r2 q w FIGURE 6.4 Control volume enclosing a turbomachine rotor.

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  Radial Flow Turbocompressors

  Design, Analysis, and Applications

  • Michael Casey, Chris Robinson(Authors)
  • 2021(Publication Date)
  • Cambridge University Press

    (Publisher)

  At times of low electrical demand, excess generation capacity is used to pump water into the higher reservoir. When there is higher demand, water is released into the lower reservoir through the same machine, which is now operating as a turbine and generating electricity. The design for pump operation takes priority; the machine will operate adequately as a turbine with accelerated flow when the water runs downhill, albeit nonoptimally. 1.3.4 Flow Direction Another important criterion for the classification of turbomachinery is the flow direc- tion relative to the axis of rotation. In purely axial rotors, the radius of the streamlines is approximately constant and the flow passes through the machine roughly parallel to the rotational axis. In purely radial machines, the radius changes significantly and the flow travels through the rotor perpendicular to the axis of rotation, as shown in Figure 1.5. In practice, axial machines tend to have some small radial velocity components as neither the inner nor the outer casing walls are perfectly cylindrical, and most radial machines have an axial component of velocity. Most radial flow compressors have axial flow at the inlet and are radial at the outlet (and vice versa for radial flow turbines), as shown in Figure 1.5. In some situations, these may qualify as mixed-flow machines because of the axial inlet and radial outlet. In the present text, the adjectives radial and centrifugal are used for all machines with a significant change of radius across the impeller and with a radial flow at exit. The name centrifugal impeller implies that the effect of centrifugal force (radius change) in generating a pressure rise across the impeller is significant. Defining the machine type based on the orientation of the leading and trailing edges can become confusing: for an axial inlet flow and radial outlet flow, the leading and trailing edges can also be designed with different sweeps with respect to the mean meridional flow.

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