Introduction to Fluid Analysis

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.