ME 2204 Fluid Mechanics

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ME 2204 Fluid Mechanics Machinery.
Dr.V.RAMJEEDean Rajalakshmi engineering
college

• Notes on lesson-

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UNIT-1

• Introduction-
• Basic conceptsproperties of fluids-
• Fluid- solid- density- sp.wt- sp.gr-.temp
• Viscosity- vapour pressure-surface
  tension-compressibility-pressure measurements-
  control volume-flow characteristics-
• Continuity equation- energy equation-
• Momentum equation-

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UNIT-2

• Flow through conduits-circular annuli-
• Boundary layer-concepts-
• Darcy-weisbach equation-
• Friction factor-Moody diagram-
• Minor losses-
• Pipes in series-
• Pipes in parallel-

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UNIT-3

• Dimensional analysis-
• Buckinghams theorem-
• Dimensionless parameters-
• Models and similitude-
• Application of dimensionless parameters-

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UNIT-4

• Rotodynamic machines-Theory-
• Velocity diagram- energy transfer-
• Eulers equation-cascade theory-
• turbines-pumps-
• Work done specific speed-
• Efficiencies- centrifugal pumps-
• Performance curves- for pumps turbines-

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Unit- 5

• Positive displacement machines-
• Reciprocating pumps-air vessels-
• Rotary pumps-
• Velocity triangle- specific speed-
• Efficiency- -
• Performance curves-

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CLOSED CIRCUIT WIND TUNNEL
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CLOSED CIRCUIT OVER VIEW
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Flow visualisation tank-
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DRAG OF BODIES

• Smooth corners- less drag-streamlining

Cd2.2
Cd0.6
Cd1.6
Cd0.4
Cd1.0
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Flow past a cylinder-
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DRAG COEFFICIENT
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Vortex shedding
Cross-flow oscillating force
V
Characteristic frequency
fS frequency (Hz) S Strouhal number 0.1850.2
(depending on Re) v flow velocity (m/s) d
cylinder dimeter (m)
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Potential Flow
U(q) 2U? sinq
P(q) 1/2 r U(q)2 P? 1/2 r U?2
Cp P(q) - P ?/1/2 r U?2 1 - 4sin2q
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STROUHAL NUMBER
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TIME EFFECT
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Add-on devices for suppression of
vortex-inducedvibration of cylinders
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Typical structures interested on VIV
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Wind flow on/around buildings
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ALONG ACROSS
Von Karman vortex street
gt 100 m tall Buildings (Holmes)
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View of the CT model inside the tunnel
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HELICAL STRAKE
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A GROUP OF CHIMNEYS
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AERODYNAMIC EXCITATIONS

• PRIMARY SOURCES
• Incoming turbulence, FT
• Vortex shedding, FW
• Motion-induced forces, FM
• F(t) Fturb(t) Fwake(t) FM
• Equation of motion
• MX CX KX FG

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Wind Effects on Bridges
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Length 850 m 2 side span each 335 m
width 12 m Bridge deck plate girder type
07.11.40 Bridge failed (4 months after
construction)Designed to with stand 45m/s
Failed at 19m/sFrequency of vibration changed
from 37 to 14 cycles/minOscillation half an
hour13.7 m sag183 m span broke
Computation of natural frequencies-Necessary
Before failure after failure
reconstructed
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Aerodynamic Coefficients
Aerodynamic Forces and Moments
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Blade Planform - Solidity

• Blade planform is the shape of the flatwise blade
  surface
• Solidity is the ratio of total rotor planform
  area to total swept area
• Low solidity (0.10) high speed, low torque
• High solidity (gt0.80) low speed, high torque

R
a
A
Solidity 3a/A
Slide Courtesy NREL USA
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Airfoil Nomenclaturewind turbines use the same
aerodynamic principals as aircraft
OR
Or
a
V
V
VR Relative Wind
a angle of attack angle between the chord
line and the direction of the relative wind, VR
. VR wind speed seen by the airfoil vector
sum of V (free stream wind) and OR (tip speed).
Slide Courtesy NREL USA
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Wind sensitive structures
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How Wind Effects are quantified?

• WIND TUNNELS 90
• FULL SCALE FIELD EXPERIMENTS 9
• COMPUTATIONAL WIND ENGINEERING
• ( Complex flow
  visualisation )

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Venturimeter-
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a200 , Re 4104
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Variation of wind velocity with time and height
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Wind speed terrain topography
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Design classification
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Features of wind speed

• Increase in mean wind speed with height
• Turbulence intensity
• Wide range of frequencies in the fluctuations

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Wind Effects on Buildings
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• MODE SHAPES AMPLITUDE
• Stretched strings attached on both ends are
  actually simpler
• Notice that each end remains fixed in place
• You are looking at different modes of oscillation
• The relative frequencies are in the ratio 1234

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Drag of cars-

• Trucks- buses- trains-
• Aerodynamic drag-
• Add-on device-
• Different shapes of cars-
• Trailer- trucks-

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Rotating cylinder-

• Applications-
• 1. Flettner rotors. Sailing ships-1924-
• 2. Drag reduction of trucks-
• 3. Magnus effect- balls- spin- cricket- tennis-
• 4. Wings to increase lift- less separation-

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TURBINES AND PUMPS

• 1. PELTON TURBINE
• 2. FRANCIS TURBINE
• 3. KAPLAN TURBINE
• 4. PUMPS-reciprocating and centrifugal
  pump-single stage and multi stage pumps-
• ( Gear pump- )

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Specific speed of turbines-
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Gear pump-
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Velocity triangle-Turbine
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Velocity Triangle-Pump
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CONCLUSIONS

• BUILDING AERO DYNAMICS
• CHIMNEYS,TOWERS,TALL BUILDINGS.
• BRIDGES- buffeting- flutter-
• TRANSMISSION LINES.
• CABLES(MARINE).
• Drag of vehicles- POLLUTION CONTROL.
• Wind mills- power generation- turbines-
• Pumps- (reciprocating centrifugal pump)
• Airplanes- helicopter- hovercraft-

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REFERENCE

• Dr.V.Ramjee Fluid Mechanics Machinery
  .Eswar press 2005
• Kumar.k.l.engineering fluid mechanics. 1995.
• Hoerner.S.F.(1965) Fluid dynamic drag.
• B.Barlow,H.Rae and A.Pope(1999) Low speed wind
  tunnel testing.
• Streeter- Bansal- som biswas- white-

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Pelton wheel bucket-
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Gear wheel-pump-