THERMODYNAMICS AND FLUID MECHANIC 20

THERMODYNAMICS AND FLUID
MECHANIC 1
THERMODYNAMICS AND FLUID MECHANICS
By Name
Course
Instructor
Institution
Location
Date

THERMODYNAMICS AND FLUID
MECHANIC 2
TABLE OF CONTENT
TABLE OF CONTENT..................................................................................................... 2
TITLE.......................................................................................................................... 3
INTRODUCTION........................................................................................................... 3
AIM OF EXPERIMENT................................................................................................ 5
METHOD...................................................................................................................... 5
EXPERIMENTAL PROCEDURE.................................................................................... 6
RESULTS..................................................................................................................... 7
Presentation of results.................................................................................................. 10
Calculation of coefficient of lift...................................................................................10
Discussion................................................................................................................... 20
Conclusion................................................................................................................... 21
Bibliography................................................................................................................ 22

THERMODYNAMICS AND FLUID
MECHANIC 3
TITLE: LIFT ON AN AEROFOIL
INTRODUCTION
In case a body or a particle is put in a flow, the particle will experience some forces from
its environment fluid (liquid or gas). This force exerted in the same direction of the flow of the
fluid is referred to as a drag. While there is another force that is orthogonal to the direction of the
fluid flow is referred to as downforce or a lift. The lift and the drag forces are generated from the
two effects which are viscosity skin friction and difference in pressure acting of the particle or
the body in a fluid. For the Airfoils which have a streamlined body, the flow will remain attached
over the surfaces of the body. This implies that drag is obtained from skin friction while the lift
is from a difference of pressure between the lower and upper surfaces of the body.
In a bluff object like a chimney or a car, the layer boundary is isolated at the same point
which forms a turbulent wake hence drag force dominates. The airfoil’s lift determined by the
angle between the direction of fluid flow and the angle between the airfoil, this angle is better
referred to as the angle of attack (Weber, 2010). When the angle of attack increases from zero to
maximum it will result in increase of lift also from zero to maximum (critical angle of attack) of
which the lift will abruptly decrease. This critical angle of attack (maximum lift) is referred to as
a stall. The drag, lift and angle of attack in aerofoil is illustrated in the following diagram;

THERMODYNAMICS AND FLUID
MECHANIC 4
Figure 1: Showing drag, lift, and angle of attack in aerofoil (Tang, 2010).
From figure 1 above it is possible to relate the drag and the lift to the kinetic of flow ½ ρ μ2 that
has a unit of pressure. Through defining the coefficient of drag and lift CD and CL respectively
such that
L=CL A ρ μ2
2 .................................................................................................1
Where A is a measure of the area of the body in fluid, L is the lift force, ρ is the fluid density and
μ the velocity of the fluid.
If the fluid is air then velocity is obtained from the Bernoulli's equation as below;
u= √ 0.9895× 2× ρw
ρa × g × H
1000 ...........................................................2
Where
u isthe velocity of air , ρa isthe air density , ρw id the water density , H is the difference ∈ pressure

THERMODYNAMICS AND FLUID
MECHANIC 5
and g is the gravitational acceleration. The pressure and of the fluid a affects the density of the
air and this is supported by the following equation
ρatm=mRT ..................................................................................................3
Where ρatmatmospheric pressure and T is absolute room temperature and R is the gas constant
(287).
AIM OF EXPERIMENT
This experiment is aimed at measuring the effect of the angle of attack on the airfoil’s lift and to
obtain the angle of stall.
METHOD
There were only three equipment which was employed in conducting this experiment, the first
equipment is a wind tunnel which has an aerofoil section (Cao, 2011). This tunnel has 23 holes
along the aerofoil centerline, 11 holes are along the top of the aerofoil while 12 holes are along
the aerofoil bottom. The second equipment used in conducting the experiment is a manometer
which was employed to measure the pressure at the openings of the holes. The third equipment
is the protractor which is employed to measure the angle of attack (α ¿ as it is adjusted (Kweon,
2010). The wind tunnel is illustrated in the following diagram;

THERMODYNAMICS AND FLUID
MECHANIC 6
Figure 2: Showing a wind tunnel
EXPERIMENTAL PROCEDURE
The wind tunnel was made to run at lower than the tunnel ́s maximum capacity, this was
very significant so that the velocity can be adjusted bit by bit. The small velocity adjustments
are made to ensure that the air velocity is constant. It is also advisable to tale the readings of the
speed gauge at the maximum speed and then reduce the speed till the manometer records a
reduced speed by about 15 %. The aerofoil was fixed to the required angle of attack, the initial
values of the angle of attack were set to be -50 , 00,50, 100 , 130, 150 and -100. The two further
angles of attack were selected, where one is before the stalls of aerofoil while the other one is
just after the aerofoil ́s stall. The wind tunnel was started and then the speed was adjusted to be
equal for all the angle of attack, the speeds were adjusted to about 85% maximum. The pressure
was recorded for every point of the aerofoil.