fluid mechanic final paper

7/28/2019 fluid mechanic final paper

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CONFIDENTAL

UNIVERSITI INDUSTRI SELANGOR

APRIL 2007 SEMESTER EXAMINATION

2/2006/2007 SESSION

SUBJECT : FLUID MECHANICS II

SUBJECT CODE : KMS 2333

DURATION : 3 HOURS

FACULTY : ENGINEERING INDUSTRY

GROUP : DEGREE IN ENGINEERING

LECTURER : ONG LEONGTECK

INSTRUCTIONS TO CANDIDATES

Answer ALL FOUR (4) questions.

Do Not Open The Question Paper Until Instructed

This Question Paper Consists of Eight (8) Printed Pages


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KMS 2333 Fluid Mechanics II

1 Air flows from a reservoir maintained at 250C and 500 kPa absolute,

as shown in Fig 1. It flows through a nozzle with throat and exit

diameters of 5 cm and 10 cm respectively. The back pressure pb inthe receiver tank is adjusted until a normal shock forms at a location

where the diameter is 8 cm. Assume the air behaves as an ideal gaswith R = 287 J.kg-1K-1 and k = 1.4. A set of tables for compressible

flow is attached at the end of this paper.

25 marks

(i) calculate the velocity and pressure at the throat

(ii) find the mach no before and after the shock

(iii) determine the pressure before and after the shock

(iv) calculate the velocity just before and after the shock

(v) what is the back pressure?

(vi) find the mass flow rate.

Shock

P01T01

Pb

D = 5 cm

D = 8 cm

D = 10 cm

Receiver

Reservoir

Fig 1


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2 (a) State the continuity and momentum equations for control volume

flows in one dimension.

25 marks

(b) Apply the equations in part (a) to the fully developed viscous flow in

a circular pipe, as illustrated Fig 2, and show that:

x

r)(p

-

r

r)(

= 0

(c) For a Newtonian fluid, the shear stress is related to the velocitygradient. Integrate the equation in part (b) to obtain the velocity

profile:

u =4

R2

dx

dp

R

r1

2

2

(d) Find the pressure difference required to drive a flow of 0.6 liters/min

of water through a pipe 1.5 cm diameter and 10.5 m long. Take the

density and viscosity of water to be 1000 kg.m-3 and 0.001 kg.m-1s-1respectively.

(e) What will be the maximum velocity in the pipe in part (d)?

Px

Px+x

r+r

r

r

xx

r

Fig 2

R


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3 Air with a uniform free stream velocity of 0.9m/s flows over a flatplate 1 m long and 0.5 m wide. Take the density and viscosity of air

to be 1.2 kg.m-3 and 1.8x10-5 kg.m-1s-1 respectively. The velocityprofile in the boundary layer can be assumed to be

U

u

=2

3

y

-

2

12

y

Determine

25 marks

(i) Boundary layer thickness at the distance x from the leading

edge of the plate

(ii) The momentum thickness at 0.5 m from the leading edge.

(iii) The wall shear stress at the distance x

(iv) The skin friction coefficient

(v) The force required to hold the plate stationary, assuming only

one side is exposed to the air flow.

(vi) If the plate is oriented with the short side in the direction offlow, would you expect the drag to increase, decrease orremain the same?

x

U

Fig 3


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4 (a) Define lift and drag 25 marks

(b) In the case of an airfoil, how does flow separation affect lift and drag

respectively?

(c) A commercial plane has a total mass of 80,000 kg and a wing

platform area of 200 m2. The plane has a cruising speed of 750 km/h

and a cruising altitude of 12,000 m where the air density is 0.031

kg.m-3

. The plane has double slotted flaps for use during takeoff andlanding, but it cruises with all flaps retracted. The lift and dragcharacteristics of the wings can be approximated by NACA 23012,

data for which is shown in Fig 4. Take the air density at ground to

be 1.2 kg/m3. Determine

(i) The takeoff speed at an angle of attack of 50

.

(ii) The stall speed with flaps

(iii) The required power to maintain the cruising speed

Fig 4

fluid mechanic final paper

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