Skip to main content

Turbulent Flow | Velocity and shear stress in turbulent flow

  Turbulent Flow in Circular Pipe


• In laminar flow ( <2000) any disturbance produced is quickly damped out by the viscous resistance.

• At higher Re (Re>4000), the fluid motion is irregular and random. There is complete mixing of fluid due to collision of fluid masses with each other. The resulting flow is known as turbulent flow. The phenomenon of turbulent motion is known as turbulence.

• In turbulent flow, velocity fluctuation causes a continuous interchange of fluid masses between neighboring layers, which is accompanied by a transfer of momentum. This momentum transfers results in developing additional shear stress besides viscous shear stress. The additional shear stress is known as turbulent shear stress.


Ad:


https://happyshirtsnp.com/


 Velocity in turbulent flow

In turbulent flow, velocity does not remain constant with time. The velocity at any instant is considered to be made up of a mean value and a fluctuating component.

Fig: Velocity variation in turbulent flow


Over large time 'T', mean of fluctuating component = 0 & the mean value is taken for computation purpose.

Similarly, in other directions,

v(t) = v + v' and w(t) = w + w'

Fluctuating component = mean velocity of layer 1- mean velocity of layer 2

  •  Features of Turbulent Flow in Pipe

Fig: Comparison of velocity profile for laminar and turbulent flow

•Flatter velocity (more uniform) profile due to mixing of fluid layers and exchange of momentum
•Large velocity gradient (du/dy) near the wall resulting in more shear
•Additional shear stresses due to turbulence
•Higher frictional loss due to the formation of eddies, mixing and curving of path lines.

Shear stress in turbulent flow







Ad:




Also read:


Labels:
Location: Kathmandu 44600, Nepal

Comments

Post a Comment

Popular posts from this blog

Nikuradse experiment | variation of frictional factor (f) for laminar and turbulent flow

  Nikuradse', a German Engineer, He by gluing uniform sand grains on the inner side of the pipe wall to artifically roughened the pipe conducted a series of well- planned experiments on pipes. Here we choose the pipe of different diameter (D) and by changing the size of sand grain which gives (Roughness height= k), We can observe from his experiment that value of (k/D) varies from about "1/1014 to 1/30"  Since from dimensional analysis 'f is the function of Reynold's no VD/ ν  and ratio of 'k/D' Where, k =Average roughness height of pipe wall, D= Diameter of pipe,   ν = Kinematic viscosity of flowing fluid, Re =VD/ ν  = Reynold's no, k/D = Relative roughness.  Sometimes, "k/D" is also replaced by "R/k" Where, R= Radius of pipe and (R/k)= Relative smoothness whose value varies from "15 to 507''. Ad: Change(Variation) of friction factor for laminar flow (Re<2000) Head loss in laminar flow (i.e. Hagen-Poisseullie equati...
Post a Comment
Read more

Reynold's Experiment | Laminar flow's in circular pipe | Shear stress distribution

  Reynold's Experiment • Osborne Reynolds (Mathematician & Physicist, UK) • In 1883, he developed a laboratory set up in which he injected Dye (i.e. a fine, threadlike stream  of colored liquid having the same density as water) at the entrance to a large glass tube through  which water was flowing from a tank .    Fig: Reynold's experiment Ad: https://happyshirtsnp.com/ • Procedure: ✓ The water from the tank was allowed to flow through glass tube into atmosphere. ✓ The velocity of flow was varied by the valve. ✓ Dye was injected into the flow through a small tube. • Observation: ✓ At the initial stage of flow, dye filament in the glass tube was in the form of straight line. This was  a laminar flow. ✓ When increasing the velocity of flow, the dye filament was no longer a straight line. The dye  filament starts to become wavy. This was a transitional flow. ✓ While further increase in velocity of flow, the wavy dye filament broke up and finally diffu...
Post a Comment
Read more

Use of double mass curve analysis | Test for the consistency of records (Double mass curve)

Use of double mass curve analysis The double mass curve is used to check the consistency of many kinds of hydrological data by comparing data for a single station with that of pattern composed of the data from the several other station in the area. The double mass curve can be used to adjust inconsistent precipitation data. The theory of double mass curve is based upon the fact that a plot of the two cumulative quantities during the same period exhibit a straight line so long as the proportionality between the two remains unchanged and the slope of the line represent the proportionality. This method can be smooth at a time series and suppress random elements in the series. In recent 30 yrs, Chinese scholars analyzed the effects of soil and water conservation measures and land use/cover changes on runoff and sediments using double mass curve method and have achieved the good results. In this study, double-mass curves of precipitation vs sediments are plotted for the two contrastive peri...
Post a Comment
Read more