What is the non-Newtonian concept introduced when applying Newton’s equations to fluids?
The stress, representing internal forces where one fluid parcel pushes on another.
What are Euler’s equations, and when do they apply?
Euler’s equations describe inviscid fluids where dissipation is ignored, and stress reduces to pressure.
What conditions justify using the inviscid model?
High Reynolds number flows where kinematic viscosity is small and aerodynamic objects have very low drag.
Why is Boundary Layer Theory needed despite inviscid models predicting lift accurately?
Because inviscid models predict zero drag, but real fluids have small, non-zero drag that requires accounting for viscous effects.
When can air be treated as incompressible?
At low speeds where its volume remains nearly constant.
What happens if incompressibility is not assumed?
The Euler equations must account for compressibility effects, especially at high speeds.
What four main flow models result from the inviscid/viscous and compressible/incompressible dichotomies?
- Inviscid incompressible
- Viscous incompressible (Boundary Layer Theory)
- Inviscid compressible
- Viscous compressible
What distinguishes aerodynamic from non-aerodynamic objects?
Their shape and orientation (e.g., angle of attack).
What does vorticity (ω) represent, and what is its condition far upstream of an aircraft?
Vorticity ω=∇×u represents local fluid rotation; it is zero far upstream.
What is persistence of irrotationality?
A condition where ω=0 remains throughout the flow in inviscid incompressible fluids due to angular momentum conservation.
How does irrotationality simplify Euler’s equations?
The velocity field can be described by a scalar potential instead of a vector field.
What is Bernoulli’s equation analogous to in mechanics?
The energy conservation equation.
Why study 2D flows before 3D flows?
2D problems (like airfoils) are simpler and use tools like complex variables, enabling easier generalization to 3D wing flows.
Why does inviscid flow predict zero lift around an airfoil, and how is this overcome?
Zero lift occurs unless circulation is introduced via a shed vortex, establishing net fluid rotation around the airfoil.
What happens in transonic regions?
Flow velocity approaches the local speed of sound, making analysis more complex and often involving shock formation
Why is lift and drag analysis simpler in supersonic flows?
Once shocks and expansion waves are understood, lift and drag become more straightforward, especially in 2D inviscid supersonic flows.
Why is turbulence important in boundary layers?
It’s essential for accurately predicting drag on flying objects.
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Midterm Prep - Ch 217
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Midterm Prep - Ch323
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Midterm Prep - Ch430
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Midterm Prep - Ch513
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Midterm Prep - Ch640
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Exam 2 - Chapter 724
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Exam 2 - Chapter 834
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Exam 2 - Chapter 933
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Exercises Ch88
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Exercises Ch98
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Chapter 11 - Shocks12
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Exercises Ch115
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Exercises Ch125
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Chapter 1316
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Chapter 1045
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Exercises 17
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Exercises 26
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Exercises 36
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Exercises 42
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Exercises 67
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Midterm 1 theory4
