Boundary Layer Lab Report Full
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Description
Boundary Layer
TITLE : FLAT PLATE BOUNDARY LAYER
OBJECTIVES The objective of this experiment are as follows:
•
To measure the boundary layer velocity profiles and observes the growth of the boundary layer for flat plate with smooth and rough surfaces.
•
To measure the boundary layer properties for the measured velocity profiles.
•
To study the effect of surface roughness on the development of boundary layer.
INTRODUCTION The conce concept pt of boun bounda dary ry laye layerr was was first first introd introduc uced ed by Ludw Ludwig ig Prand Prandtl, tl, a Germa German n aerodynamicist in !"#. The boundary layer concept provided the lin$ that had been missin missing g betw betwee een n theo theory ry and and practi practice ce.. %urth %urtherm ermore ore,, the the boun bounda dary ry layer layer conce concept pt permitted the solution of viscous flow problems that would have been impossible through application the &avier'(to$es e)uation to the complete flow field.
*s for flow in a duct, flow in a boundary layer may be laminar or turbulent. There is no uni)ue value of the +eynolds number at which transition from laminar to turbulent flow occur in a boundary layer. *mong the factors that affect boundary'layer transition are pressure pressure gradient gradient,, surface surface roughne roughness, ss, heat heat transfe transfer, r, body forces forces and free stream stream disturbances. n many real flow situations, a boundary layer develops over a long, essentially flat surface. * )ualitative picture of the boundary layer growth over a flat plate is shown in figure below.
%igure .: -oundary layer on a flat plate /ertical thic$ness exaggerate greatly0
Boundary Layer
THEORY
(ome measures of boundary layers are described in figure .1 below.
%igure .1 : -oundary Layer thic$ness definitions
The boundary layer thic$ness, δ, is defined as the distance from the surface to the point where the velocity is within percent of the stream velocity. The displacement thic$ness,
δ2, is the the dista distance nce by which which the solid solid bounda boundary ry would would have to be displa displaced ced in a frictionless flow to give the same mass deficit as exists in the boundary layer.
The momentum thic$ness, θ, is define as the thic$ness of a layer of fluid of velocity, 3 free stream velocity0, for which the momentum flux is e)ual to the deficit of momentum flux through the boundary layer. The -lasius4s exact solutions to the laminar boundary yield the following e)uations for the above properties. δ =
5.0 x Re x
∗
δ
1.72 x =
Re x
θ =
0.664 x Re x
Boundary Layer
5ue to the complexity of the flow, there is no exact solution to the turbulent boundary layer. The velocity profile within the boundary layer commonly approximated using the 67 power law. u U
1
y 7 = δ
The properties of boundary layer are approximated using the momentum integral e)uation, which result in the following expression.
δ =
0.370 x 1
Re x 5
δ ∗
=
0.0463 x 1
Re x 5
θ =
0.036 x 1
Re x 5 *nother measure of the boundary layer is the shape factor, 8, which is the ratio of the displacement thic$ness to the momentum thic$ness, 8 9 δ26θ. %or laminar flow, 8 increases from 1. to ;.< at separation. %or turbulent boundary layer, 8 increases from .; to approximately 1.< at separation.
EXPERIMENT APPARATUS
Boundary Layer
The experiment set up consists of: .
*irflow -ench
1.
Test *pparatus
;.
Total and static tube pressure probes and multi tube manometer.
Plenm otlet On-off switch
Damper control rod
PROCEDURES
Boundary Layer
. The apparatus has been set up on the bench as shown on figure # uses the flat plate with the smooth surface for the first part of the experiment. 1. (et the pitot tube about .#;m6s
+eynolds number, +e x 9
Ux ν
9
1!.43 × 40 × 10 −3 1.30 × 10
−5
9 .1
#. +ough surface with distance from the leading edge, x 9
>."; x " '# ;.;;; x " '# .1>7 x " '# 1. x " '; 1.";> x " '# .# x " '# .1>7
%or smooth surface:
%or rough surface:
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