Fluid Mechanics Primer

Fluids mechanics deals with the Navier-Stokes equations and in this blog, we will discuss the beauty of these equations that describe fluid flow and how fluid mechanics impact our everyday world.

Fluid mechanics has a historical legacy that goes back to Prandtl’s original ideas of simple control volume theory. It was built around rigorous physical intuition and a theoretical foundation. Understanding Fluid Mechanics gives a deeper appreciation of our beautiful world and solving fluid mechanics problems makes one creative and critical thinker.

In nature, matter exists in three phases – solids, liquids, and gases. Broadly speaking, both liquid and gases can be regarded as fluids. Fluid dynamics is the study of such fluids in motion.

Understanding the principles of fluid dynamics is critical in many engineering applications. The engineers in the aerospace and automotive industries rely on these fundamental concepts to design and optimize the shapes of these means of transportation. The design of space shuttles and rockets used to carry humans and terrestrial technologies, such as the Hubble Space Telescope, into space requires a deep understanding of fluid dynamics.

Fluid Statics: Fluid at rest

Fluid Kinematics: Fluid in motion (Neglecting the forces causing the motion).

Fluid Dynamics: Fluid in motion (Considering the forces causing the motion).

 

Bird Flight – Extreme Aerodynamics

Downwash & Induced Drag

The flow pattern at the tip of the finite wing generates a vortical flow field. The trailing vortices create a ‘downwash’ at the wing that rotates the freestream velocity downwards vectorially. These vortices make the resultant lift force vector rotate backward, which gives rise to a force that is in the direction of the flow. This is in addition to the ‘lift force’ (an upward force at right angles to the flow direction). This ‘drag force‘ is called the ‘induced drag’ as it is accompanied by the production of lift.

Linearized Theory

The above discussion regarding forces generated due to uniform motion of aerodynamic elements(airfoils/wings) does not necessarily apply to bird flights.
Birds generate both lift and thrust forces using the same aerodynamic surfaces, contrary to the mechanism of aerospace vehicles where the lift and thrust generation are decoupled.

Lift and thrust generation in flapping flight (Lighthill 1974)

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