# Lab Report - Turbulence

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13-Jan-2016

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Fluid Dynamics Lab Report about Reynolds number at different velocities with ANSYS simulation

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Faurecia souscrit au principe d'quit en matire d'emploi

Lab ReportNilesh Dhondo

Idea Background The Light Bulb Moment3

The Company and Its Environment3

The Company and Its Product5

Subjects5

Course Modes5

Interaction5

Website Structure6

The Company and Its Price7

Subscrption Plans7

Member Categories8

The Company and Its Promotion9

Theoretical background

Reynolds Number

Reynolds Number is a non dimensional number expressed as the ratio between inertia forces and frictional viscous forces.

Laminar Flow versus Turbulent flow: Differentiated by the Reynolds numbers (characteristic Reynolds critical numbers are different for different fluids). Laminar flow is immiscible flow, turbulent flow is miscible flow.Flow Around a Cylinder

Impact Point and Detachment Point

Pictures

A. Reynolds Number is 20.

Velocity Magnitude Contour LinesWe notice that strata do not mix, but the current lines are asymetrical. There is an impact (stagnation point) and a detachment point. Behind the detachment point, vortices start to form. Reynolds number is between 1 and a Reynolds Critical 1 Number.

Static Pressure Distribution

For the pressure distribution we can calculate the pressure coefficient Cp.

Cp is defined as being . Cp depends on the angle of attack. At the impact point Cp is 1, then it becomes negative, leading to a depression area (to the right) with Cp negative (p < p inf). Wall Shear Stress

The wall shear stress is proportional to the rate of change of velocity with respect to the y axis. In the boundary layer, velocity increases very fast, from 0 at the contact with the surface of the cylinder to 0.98 of v inf. Hence wall shear stress is high in the boundary layer, being 0 outside (according to Prandtl, outside the boundary layer velocity is constant, almost equal to v inf, hence the rate of increase is 0 hence the shear stress is 0, the fluid can be considered to be ideal). Behind the dettachment point, shear stress is low.Vorticity Magnitude

We can see at Reynolds number 20, there are 2 symmetrical vortices being formed to the right, after the detachment point, where the velocity changes direction.Velocity Magnitude versus Position This graph represents the distance against the magnitude of the velocity. We can see the velocity is approximately 0 at the contact with the walls of the cylinder, then a logarithmic distribution of the velocity from 0 m to 0.2 m and from 0.3 m to 0.5 m.Static Pressure Along y axisThis graph shows pressure on the y axis. We can see the area of depression (low pressure)Static Pressure Along x axisThis graph shows pressure on the x axis, again we can see the area of depression.B. Reynolds Number is 300

Velocity Magnitude Contour LinesReynolds number is between a Reynolds Critical 1 Number and a Reynolds Critical 2 Number. Von Karman vortices start to form.

Static Pressure Distribution

For the pressure distribution we can calculate the pressure coefficient Cp.

Cp is defined as being . Cp depends on the angle of attack. At the impact point Cp is 1, then it becomes negative, leading to a depression area (to the right) with Cp negative (p < p inf). Wall Shear Stress

The wall shear stress is proportional to the rate of change of velocity with respect to the y axis. In the boundary layer, velocity increases very fast, from 0 at the contact with the surface of the cylinder to 0.98 of v inf. Hence wall shear stress is high in the boundary layer, being 0 outside (according to Prandtl, outside the boundary layer velocity is constant, almost equal to v inf, hence the rate of increase is 0 hence the shear stress is 0, the fluid can be considered to be ideal). Behind the dettachment point, shear stress is low.Vorticity Magnitude

We can see at Reynolds number 20, there are 2 symmetrical vortices being formed to the right, after the detachment point, where the velocity changes direction.Static Pressure Along y axisThis graph shows pressure on the y axis. We can see the area of depression (low pressure)Static Pressure Along x axisThis graph shows pressure on the x axis, again we can see the area of depression.C. Reynolds Number is 1000

Velocity Magnitude Contour LinesWe notice that strata do not mix, but the current lines are asymetrical. There is an impact (stagnation point) and a detachment point. Behind the detachment point, vortices start to form. Reynolds number is between 1 and a Reynolds Critical 1 Number.

Static Pressure Distribution

For the pressure distribution we can calculate the pressure coefficient Cp.

Cp is defined as being . Cp depends on the angle of attack. At the impact point Cp is 1, then it becomes negative, leading to a depression area (to the right) with Cp negative (p < p inf). Wall Shear Stress

The wall shear stress is proportional to the rate of change of velocity with respect to the y axis. In the boundary layer, velocity increases very fast, from 0 at the contact with the surface of the cylinder to 0.98 of v inf. Hence wall shear stress is high in the boundary layer, being 0 outside (according to Prandtl, outside the boundary layer velocity is constant, almost equal to v inf, hence the rate of increase is 0 hence the shear stress is 0, the fluid can be considered to be ideal). Behind the dettachment point, shear stress is low.Velocity Magnitude versus Position This graph represents the distance against the magnitude of the velocity. We can see the velocity is approximately 0 at the contact with the walls of the cylinder, then a logarithmic distribution of the velocity from 0 m to 0.2 m and from 0.3 m to 0.5 m.Static Pressure Along x axisThis graph shows pressure on the x axis. We can see the area of depression (low pressure)