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MECH 5304- Computational Fluid Dynamics

Dr. Brian R. McAuliffe

Student # 100878010

Praveen Jose

February 26, 2013

Abstract

In this project numerical investigation of the flow over a given airfoil NACA 2412 is

conducted with the help of computational fluid dynamics. The aim is to examine the

 boundary layer distribution and the separation of flow over the airfoil. This solved

using commercial CFX .14.

Introduction

An airfoil is anybody which when set at a suitable angle to a given airflow produces

aerodynamic forces. The efficiency of the airfoil depends on the geometry of the

airfoil .Each airfoil is designed to obtain maximum lift with minimum drag .Anefficient aircraft requires an efficient wing with minimum thickness for

aerodynamic quality and adequate thickness to accommodate fuel .All these design

restriction rely much on the design and selection of the airfoil. The selection of

airfoil becomes complex for supersonic aircraft as the thickness should be kept

minimum but it restricts the volume of fuel that can accommodate in wing.

Moreover the shape of the airfoil determines the flow over the airfoil at various

angle of attack. The boundary layer thicknesses and the flow separation largely

depends on the chamber of the airfoil. The stall of the aircraft arises due to

separation of the flow over the wing at high angle of attack where there is no more

flow passing over the wing. So it necessary to consider an airfoil parameters before

using it in an aircraft.

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Boundary layer distribution is one of the main aspects we are considering in our

 project. The concept of a boundary layer is crucial to the understanding of the flow

around an obstacle at large Reynolds numbers. The boundary layer thickness, δ, is

the distance across a boundary layer from the wall to a point where the flow velocity

has essentially reached the 'free stream' velocity. The boundary layer thickness isarbitrarily defined as the point at which the velocity reaches 99% of the undisturbed

free stream velocity.

For a smooth airfoil at low Mach number transition of the boundary layer usually

occurs as a result of the development of Toll Mein Schlichting (TS) waves [1].

These linear waves breakdown into nonlinear three-dimensional instabilities and

finally form turbulent spots that coalesce to form a turbulent boundary layer. This

 process takes a finite distance to develop from the initial growth of the TS waves to

a fully developed turbulent boundary layer. The introduction of surface roughness

into the preceding processes can greatly enhance certain growth regimes or bypass

others altogether.

The displacement thickness, δ* is the distance by which a surface would have to be

moved in the direction perpendicular to its normal vector away from the reference

 plane in an inviscid fluid stream of velocity to give the same flow rate as occurs

 between the surface and the reference plane in a real fluid

The definition of the displacement thickness for  compressible flow is based on mass

flow rate:

The definition for  incompressible flow can be based on volumetric flow rate, as the

density is constant:

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