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- 1. PRESENTATION ON FLUID FLOW PHENOMENA
- 2. FLUID FLOW PHENOMENA Fluid:In physics a fluid is a substance that continuously deforms under an applied shear force. A fluid is a substance that doesn’t permanently resist distortion. An attempt to change the shape of mass of a fluid results in sliding of the layer of the fluid over one another. Fluid Flow:Potential Flow: - The flow of incompressible fluid with no shear is known as Potential flow It has some important characteristics1. Neither circulation nor eddies forms within the stream. Hence the potential flow is known as irrotational flow. 2. Friction cannot develop since there is no existence of shear stress & hence there is no dissipation of mechanical energy into heat energy. Boundary layer:The effect of solid boundary on the flow is confined to the layer of the fluid immediately adjacent to the solid boundary. This layer is called Boundary Layer & also the shear stress are confirm to this part of the fluid only. Parts of fluid:(1)Boundary Layer (2)Remaining fluid
- 3. RHEOLOGICAL PROPERITIES OF FLUIDS Newtonian & Non-Newtonian fluid:Newtonian fluid – Fluid flow in simple linearity are called Newtonian fluid. In a Newtonian fluid the shear stress is proportional to the shear rate , and the proportionality constant is called the viscosity. du g c dy where μ = co-efficient of viscosity Exmp- Water , Gasses etc Non-Newtonian fluid1. The curve starts from origin & concave downwards represents Pseudoplastic fluid & this type of fluid is said to be shear rate –thinning. Exmp – Polymer solutions , starach suspensions etc. FIGURE : Shear stress vs shear rate 2. The curve starts from origin & concave upwards represents Dilatant fluid & this type of for fluid is said to be shear rate –thickening. Newtonian & Non-Newtonian fluid Exmp – Wet beach sand , starch in water etc 3. The straight line having some intercepts in y – axis represents Bingham plastic . This type of fluid do not flow at all until a threshold shear stress attained & then flow linearly at shear stress 0 0 greater than Exmp – Sludge
- 4. Reynolds stresses :- The stress is much larger in turbulent flow than the laminar flow . Since the shear stress is higher in turbulent flow Turbulent shear stress are called Reynolds stresses Eddy viscosity :- By analogy , he relationship between shear stress and velocity gradient in a turbulent stream is used to define an eddy viscosity EV . where E v = eddy viscosity du t g c Ev dy Also we know , du μ = co-efficient of viscosity g c dy The above two expression is almost similar .Hence eddy viscosity is analogous to μ . We know, And also, Where m N RE N RE DV DV DV where ν=kinematic viscosity DV DV DV Ev Ev m E v =Eddy diffusivity of momentum = Here kinematic viscosity is analogous to eddy diffusivity.
- 5. BOUNDARY LAYERS Here the flow of fluid is parallel to a thin plate LM . A boundary is define as the part of a moving fluid in which a fluid is influence by a solid boundary . The velocity of the fluid as solid-liquid interface is zero. The velocity increases with distance from the plate as shown in figure. Each of the curve represents the velocity profile for definite value of x , the distance from the leading edge of the of the plate. The curves changes slope rapidly near the plate . Line OL represents an imaginary surface , which separates the fluid stream into two parts , one in which fluid velocity is constant and the other where the velocity varies from zero to a velocity substantially equal to that of un disturbed fluid.
- 6. LAMINAR & TURBULANT FLOW IN BOUNDARY LAYER Flow near the boundary layer is laminar flow. Since velocity is very low as we move further from the solid boundary the velocity is fairly large and hence the floe become turbulance. There are three layers:1. Viscous sublayer 2. Buffer layer 3. Turbulent zone
- 7. BOUNDARY LAYER FORMATION IN STRAIGHT TUBUES Considering a straight, thin-walled tube with fluid entering it at a uniform velocity. As shown in the above fig. A boundary layer begins to form at the entrance to the tube and as the fluid move to the first part of the channel , the boundary layer thickens. During this stage the boundary layer occupies only a part of the tube & total stream consists of a core of fluid moves like a road like manner . But the velocity of fluid is constant. In the boundary layer , the velocity varies from zero to constant velocity existing in the core . As we further move down to the tube , the boundary layer occupies an increasing portion of the cross-section of the tube. At this point , the velocity distribution in the tube reaches its final point & remains unchanged for the remaining part of the fluid . Such flow with an unchanging velocity distribution is called ‘Fully Developed Flow' .
- 8. TRANSITION LENGTH The length of the entrance region of the tube necessary for the boundary layer to reach the centre of the tube & for the fully developed flow to be established is called ‘TRANSITION LENGTH’. We can express it by (Xt / D)=0.05*NRe Xt = Transition Length D= Diameter of the tube
- 9. THANK YOU PREPARED & PRESENTED BY:1.SRIJITA PODDER 2. KUNAL SANKAR DEY 3.RUPAK BHOWMIK 4.DEBOSREE DATTA 5.SONALI 6.SUGAM BHOWMIK

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