Fluid Flow Concepts Flow Classification Ideal fluid flow Frictionless(zero viscosity) ● Incompressible Can be solved mathematically Real fluid flow Shear stress develops where there is velocity gradient Fluid in contact with wall has zero velocity Pipe wall Ideal fluid Real fluid Non-uniform velocity Shear stress niform velocity eXIstS Zero shear stress Fluid close to wall has zero velocity
Fluid Flow Concepts Flow Classification : Ideal Fluid Flow • Frictionless (zero viscosity) • Incompressible • Can be solved mathematically Real Fluid Flow • Shear stress develops where there is velocity gradient • Fluid in contact with wall has zero velocity Pipe Wall Ideal Fluid : Uniform velocity Zero shear stress Real Fluid : Non-uniform velocity Shear stress exists Fluid close to wall has zero velocity
Flow Classification Laminar flow Occurs at low reynolds number Fluid moves along smooth layers Motion governed by newton's law of viscosity Turbulent flow e Occurs at high reynolds number e Fluid moves along irregular. fluctuating and random paths
Flow Classification Laminar Flow • Occurs at low Reynolds number • Fluid moves along smooth layers • Motion governed by Newton’s law of viscosity Turbulent Flow • Occurs at high Reynolds number • Fluid moves along irregular, fluctuating and random paths
Flow Classification Rotational (vortex) flow Fluid undergoes net rotation about some axis Irrotational flow Fluid has no net rotation, only linear translation e All ideal fluid flows are irrotational flows Variation of fluid properties(velocity, pressure, density, temperature etc) Temporal variation Steady flow -Properties at a point not changing with flow Unsteady flow-changing with time Spatial variation Uniform flow- Properties at an instant do not change with space Non-uniform flow-changing from point to point Four possible flow types · Steady uniform flow Steady non-uniform flow Unsteady uniform flow Unsteady non-uniform flow
Flow Classification Rotational (vortex) flow • Fluid undergoes net rotation about some axis Irrotational flow • Fluid has no net rotation, only linear translation • All ideal fluid flows are irrotational flows Variation of fluid properties (velocity, pressure, density, temperature etc) Temporal Variation : • Steady flow –Properties at a point not changing with flow • Unsteady flow – changing with time Spatial Variation : • Uniform flow – Properties at an instant do not change with space • Non-uniform flow – changing from point to point Four possible flow types : • Steady uniform flow • Steady non-uniform flow • Unsteady uniform flow • Unsteady non-uniform flow
Flow Classification One-dimensional flow Flow properties are function of time(t) and one space coordinate(e.g x) Two-dimensional flow Flow properties are function of time(t) and two space coordinates(e.g. x, y) TThree-dimensional flow Flow properties are function of time(t)and three space coordinates (x, y, z
Flow Classification One-dimensional flow • Flow properties are function of time (t) and one space coordinate (e.g. x) Two-dimensional flow • Flow properties are function of time (t) and two space coordinates (e.g. x, y) Three-dimensional flow • Flow properties are function of time (t) and three space coordinates (x, y, z) x x y
Engineering Simplification Many engineering problems are simplified as one dimensional problems Pipe flow Actual Assumed 1-D VdA= av Vm=o/A Open Channel Actua A ssumed Vm=Q/A
Engineering Simplification Many engineering problems are simplified as onedimensional problems Pipe Flow : Open Channel : Vm = Q/A v Vm Actual Assumed 1-D Actual Assumed 1-D V Vm V Q A VdA AV m A m = / =