TLK-215 Mekanika Fluida II

TLK-215 Mekanika Fluida II
The Flow of Fluid
Flow regimes
Basic equations of flow regime
(Darcy weisbach, Reynold number and
Froude number
Keadaan Aliran
Tinjauan berdasarkan:
1. Pengaruh viskositas
- laminar,
- turbulen dan
- transisi
2. Laminaritas:
 Persamaan Darcy Weisbach (Bil. Darcy: Stanton. Blasius,
Prandtl-vonKarman)
3. Turbulensi:
 Persamaan Reynold : bervariasi terhadap media saluran
4. Pengaruh gravitasi
 Persamaan Froude, menentukan sifat kritis suatu alian
berdasarkan perbandingan kecepatan dan kedalaman hidroulis
Rerfresh: Introduction
 It depends on whether the fluid is forced to flow over

Fluid flow is classified as
a surface or in a conduit.
• external
• internal
 Internal and external flows exhibit very different

characteristics.
Internal flow
• where the conduit is completely filled with the fluid,
• the flow is driven primarily by a pressure difference.
Open-channel flow
• partially filled by the fluid and
• the flow is partially bounded by solid surfaces
• the flow is driven by gravity alone
 Example: as in an irrigation ditch
Refresh: Introduction
• Liquid or gas flow through pipes or ducts
 commonly used in heating and cooling
applications and fluid
distribution networks.
• The fluid in such applications is usually forced

to flow by a fan or pump through a flow
section.
• Particular attention to friction during flow

through pipes and ducts.
 directly related to the pressure drop and
head loss
• The pressure drop is then used to determine

the pumping power requirement.
• A typical piping system involves pipes:

- different diameters connected to each other
- various fittings or elbows to route the fluid
- valves to control the flow rate
- pumps to pressurize the fluid
Refresh: Introduction
• The terms pipe, duct, and conduit are usually

used interchangeably for flow sections.
In general,
• flow sections of circular cross section  pipes
(especially when the fluid is a liquid)  circular
pipe
• flow sections of noncircular cross section 
ducts (especially when the fluid is a gas) 
rectangular duct
• Small diameter pipes  tubes.
STATE OF FLOW
The state or behaviour of open channel flow

is governed basically by
- the viscosity and gravity effects relative to
- the inertial forces of the flow
Pipe Flow
• For many engineering problems
there is no free surface: pipe flow
• The velocity profile in fully developed

pipe flow is parabolic in laminar flow,
but much fuller in turbulent flow.
• Note that u(r) in the turbulent case is

the time-averaged velocity component
in the axial direction (the overbar on u
has been dropped for simplicity).
• For Pipe Flow Hydraulic diameter, Dh is defined as
Dh = 4 Ac/P
so that the relation between hydraulic

radius and hydraulic diameter is:
• NRe < 2000, laminer

• 2000 < NRe < 4000, transisi
• 4000 < NRe, turbulen
For Open Channel Flow
 Reynold Number is constant for the entire uniform flow section of an open
channel flow
Kinematic viscosity
is the ratio of absolute (or dynamic) viscosity to density
- a quantity in which no force is involved.
Effect of Viscosity
Note:
Dalam dinamika fluida , dalam
kerangka mekanika
kontinum , parsel fluida adalah
sejumlah kecil fluida, yang
dapat diidentifikasi sepanjang
dinamisnya saat bergerak
dengan aliran fluida .
Beberapa References Kriteria turbulensi
Jika tinta jatuh di aliran:
Laminer
Turbulen
Turbulensi aliran
Hydraulic radius
relations for various
open-channel
geometries.
Typical Open Channel Shapes
Unsur-unsur geometris penampang saluran
Unsur-unsur geometris penampang saluran
Bilangan Froude
Bilangan Froude
Regim aliran
Bilangan Froude
Bilangan Froude
Bilangan Froude
Bilangan Froude
Subcritical flow and

supercritical flow in
terms of critical
depth.
Bilangan Froude
(a) Flow through a sluice gate.

(b) A hydraulic jump observed in a water channel.
Contoh
regim aliran
Reynold Number vs Froude Number
Regim of flow
Persamaan Darcy Weisbach
The Darcy-Weisbach equation
• is valid for fully developed, steady state and incompressible

flow.
• The friction factor or coefficient (λ) depends on
A. the flow (the Reynolds Number) , if it is:
- laminar,
- transient or
- turbulent - and
B. the roughness of the tube or duct.

Bilangan Darcy dan Reynold
Learning check!
Suatu aliran dalam saluran dengan penampang berbentuk
persegi panjang dengan lebar saluran 2 m melalui titik
pemantauan dan diketahui kedalaman aliran 1 m dengan
kecepatan aliran hasil pengukuran di 0,2 kedalaman 0,8
m/det dan di 0,8 kedalaman 1,2 m/det.
a. Berapakah kecepatan aliran bila di hilir saluran

kedalamannya 0,25 m?
b. Apa jenis aliran yang terjadi ?
Learning check!
Water is flowing steadily in a 0.4-m-wide rectangular
open channel at a rate of 0.2 m3/s (see the Fig.). If the
flow depth is 0.15 m, determine the flow velocity and
if the flow is subcritical or supercritical.
TO BE CONTINUED  !

TLK-215 Mekanika Fluida II

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TLK-215 Mekanika Fluida II

The Flow of Fluid

 It depends on whether the fluid is forced to flow over

 Internal and external flows exhibit very different

• The fluid in such applications is usually forced

• Particular attention to friction during flow

• The pressure drop is then used to determine

• A typical piping system involves pipes:

• The terms pipe, duct, and conduit are usually

The state or behaviour of open channel flow

• The velocity profile in fully developed

• Note that u(r) in the turbulent case is

so that the relation between hydraulic

• NRe < 2000, laminer

Subcritical flow and

(a) Flow through a sluice gate.

• is valid for fully developed, steady state and incompressible

B. the roughness of the tube or duct.

a. Berapakah kecepatan aliran bila di hilir saluran

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