Introduction

When a viscous fluid flows along a fixed impermeable wall, or past the rigid surface
Of an immersed body, an essential condition is that the velocity at any point on the
Wall or other fixed surface is zero. The extent to which this condition modifies the
General character of the flow depends upon the value of the viscosity. If the body is of
Streamlined shape and if the viscosity is small without being negligible, the modifying
Effect appears to be confined within narrow regions adjacent to the solid surfaces; these
Are called boundary layers. Within such layers the fluid velocity changes rapidly from
Zero to its main-stream value, and this may imply a steep gradient of shearing stress;
As a consequence, not all the viscous terms in the equation of motion will be negligible,
Even though the viscosity, which they contain as a factor, is itself very small.
A more precise criterion for the existence of a well-defined laminar boundary layer is
That the Reynolds number should be large, though not so large as to imply a
breakdown
Of the laminar ow.
Objective
 To become familiar with a boundary layer and its parameters.
 Investigation of the boundary layer on the flat plate.
 Influence of surface roughness on the formation of a boundary layer.
 Internal friction of the glass.

Device description
The accessory unit HM 225.02 boundary layer apparatus is intended to be installed in the HM
225 air flow Bench.

1) micrometer screw
2) Pitot tube, horizontally adjusted
3) Static tube
4) Plate, vertically arranged
5) Base cabinet
6) Clamp fastener seat
7) Side body
8) Scale
9) Knurled screw for plate

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The accessory unit inserted in the measurement section with clamp fastener. A plate is available
to study the boundary layer, which has one smooth and rough surface. The plate is pushed into
the unit and is vertically adjustable to vary the distance to the Pitot tube.

The unit compromises two measuring points:

 A pitot tube to measure the total pressure. Adjusted horizontally using micrometer
screw.
 A static tube to measure the static pressure.
By varying the vertical position of the plate and the horizontal position of the pitot tube,
it is possible to record velocity profiles transverse and longitudinally to the flow.
Side bodies used to measure section. Thus the boundary layer phenomena can be superimposed
using a progressive or digressive pressure curve.

Procedures
1) Measure ambient temperature and air pressure and use these to determine the
current air density.
2) Push the plate to the vertical position (distance from the leading age of the plate)
and secure with knurled screw.
3) Turn on the bench.
4) Read the atmospheric pressure off a manometer tube not connected to a measuring
point.
5) Read the measure values for p(total) and p(stat) off the manometer tubes.
6) Use the micrometer screw to increase the horizontal position y (horizontal distance
from the plate) and read measured values for p(total) and p(stat) off the manometer
tubes.
 Repeat this step several times to obtain a series of measurements.

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 Analysis of the experiment

Horizont Vertical position x in mm

al
position
10 30 60 100
y in mm Pt Ps Pt Ps Pt Ps Pt Ps

0 60 120 70 12 68.5 120 71 120

0
0.5 62 120 67 12 68 120 68 120
0
1 61 120 66 12 67 120 67 120
0
3 63 120 63 12 64 120 65 120
0
5 62.5 120 62 12 63 120 63 120
0

Table: - measured values for experimental setup with smooth plate.

Pt- The total pressure

Ps- the stat pressure
Pdyn- the dynamic pressure

v- Velocity

Calculation
for calculating the dynamic pressure.at x=10 and y=1

Pt=61
Ps=120

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 Pdyn= Pt- Pt = 61-120 =59

for calculating the flow velocity.

Pdyn= Pt- Pt
ρ=1.2041 kg/m^3 in kg/m^3
v=√ 2 P dyn /¿ ¿ ρ
V= √ 2∗ 59/¿ ¿1.2041
V=69 m/s

Chart Title
25

20

15

10

0
0 1 2 3 4 5 6 7 8

horizontal position x in mm Series4

Series6 Series8
Series10

The graph is drawn by using Microsoft excel software using the data.

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Result

It can clearly see that the flow velocity v

 Decrease with increasing vertical distance x to the loading edge of the plate.
 Increase with the increasing horizontal distance y to the plate.
The unaffected flow velocity v`(ambient velocity according to the table is 19.96.
The velocity at the end of the boundary is calculated using
V (δ) =0.999*v`
=0.999*19.96
=19.94 m/s
The boundary layer thickness δ the horizontal distance y to the plane in which V (δ) is
reached is determined by interpolation and extrapolation of th55TFCCY7 e velocity.
Flow velocity in m/s boundary layer thickness
19.5 9
19.94 15

After interpolating this value we get δ=14.7313.

Vertical position x in mm
10 30 60 100
Boundary 1.1 2.6 3.5 4.3
layer
thickness δ
in mm

5
 Boundary layer thickness δ in
mm
12

10

0
0 2 4 6 8 10 12

The boundary layer thickness δ increase with increasing vertical distance x to the
leading edge of the plate. At a distance to the leading edge of the plate of about the
boundary layer thickness reaches about 6,8mm.the boundary layer thickness does
not change with further increasing distance to the leading edge of the plate.

Conclusion
It can be concluded that this experiment achieved its objectives. The
boundary layer velocities for the flat plate with smooth and rough surface have
been obtained where the data can be seen from the table. The velocity profiles of
the flat plate have been obtained through data read and the graphs have been
plotted. The roughness of the flat plate gives the variety of the velocity profile. It
can be concluded that the surface roughness of the flat plate influence the velocity
profiles where the smooth surface will delay the transition while the rough surface
will make the transition become faster.

REFERENCE

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- Dr. Hamid Rahai, MAE 440 Aerodynamics Laboratory Experiments, California
State University Long Beach, spring 2007

-John J. Bertin, Aerodynamics for Engineers, 4th edition, 2002

-Schlichting H. 1979. Boundary-layer theory. 7th Ed. New York: McGraw-

Hill.