Flow simulations are
widely used in engineering applications ranging from flow around airplane wings
and hydraulic turbines to flow in blood vessels and other circulatory systems. We may gain a better
understanding of the motion of fluid around objects as well as the fluid
behavior in complex circulatory systems by conducting fluid analysis.
Computational fluid dynamics
(CFD) simulation complements experimental testing, helps reduce cost and turnaround
time for design iterations, and has become an indispensable tool whenever practical
design involving fluids is required.
In
fluid dynamics, the motion of a fluid is mathematically described using
physical quantities such as the flow velocity u, flow pressure p, fluid density
ρ, and fluid viscosity ν. The flow velocity or flow pressure is different at a
different point in a fluid volume. The objective of fluid simulation is to track
the fluid velocity and pressure variations at different points in the fluid domain.
CFD
is useful in a wide variety of applications and here we note a few to give you
an idea of its use in industry. The
simulations shown below have been performed using the FLUENT software. CFD can be used to simulate the flow over a
vehicle. For instance, it can be used to study the interaction of propellers or
rotors with the aircraft fuselage. The
following figure shows the prediction of the pressure field induced by the
interaction of the rotor with a helicopter fuselage in forward flight. Rotors
and propellers can be represented with models of varying complexity.
The
temperature distribution obtained from a CFD analysis of a mixing manifold.
This mixing manifold is part of the passenger cabin ventilation system on the
Boeing 767. The CFD analysis showed the effectiveness of a simpler manifold design
without the need for field testing.
Bio-medical
engineering is a rapidly growing field and uses CFD to study the circulatory
and respiratory systems. The following figure shows pressure contours and a
cutaway view that reveals velocity vectors in a blood pump that assumes the
role of heart in open-heart surgery.
CFD
is attractive to industry since it is more cost-effective than physical
testing. However, one must note that complex flow simulations are challenging
and error-prone and it takes a lot of engineering expertise to obtain validated
solutions.
Aircraft
design was traditionally based on theoretical aerodynamics and wind tunnel
testing, with flight-testing used for final validation. CFD emerged in the late
1960's. Its role in aircraft design increased steadily as speed and memory of
computers increased. Today CFD is a principal aerodynamic technology for aircraft
configuration development, along with wind tunnel testing and flighttesting.
State-of-the-art
capabilities in each of these technologies are needed to achieve superior performance
with reduced risk and low cost.
The
application of CFD to reduce the drag of a wing by adjustment of pressure
gradient by shaping and by suction through slotted or perforated surfaces. The
drag of an aircraft can be reduced in a number of ways to provide increased
range, increased speed, decreased size and cost, and decreased fuel usage. The
adjustment of pressure gradient by shaping and using laminar boundary-layer
control with suction are two powerful and effective ways to reduce drag. This
is demonstrated with a calculation method for natural laminar flow (NLF) and
hybrid laminar flow control (HLFC) wings.
The
application of CFD to ground-based vehicles, in particular to automobile
aerodynamics development. The use of CFD in this area has been continuously
increasing because the aerodynamic characteristics have a significant influence
on the driving stability and fuel consumption on a highway. Since the aerodynamic
characteristics of automobiles are closely coupled with their styling, it is
impossible to improve them much once styling is fixed. Therefore, it is necessary
to consider aerodynamics in the early design stage.
CFD
also finds applications in internal flows and has been used to solve real
engineering problems such as subsonic, transonic and supersonic inlets, compressors
and turbines, as well as combustion chambers and rocket engines.
