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Questions and Answers
What characterizes a laminar boundary layer?
What characterizes a laminar boundary layer?
- Smooth and parallel flow of fluid particles. (correct)
- Presence of eddies and vortices.
- Chaotic flow with high skin friction drag.
- Stability against separation.
What effect does surface roughness have on flow characteristics?
What effect does surface roughness have on flow characteristics?
- It promotes turbulence. (correct)
- It decreases turbulence.
- It enhances laminar flow stability.
- It has no effect on flow.
Which statement about turbulent flow is true?
Which statement about turbulent flow is true?
- It has lower skin friction drag than laminar flow.
- It is characterized by smooth and orderly flow.
- It occurs at lower Reynolds numbers.
- It involves chaotic and irregular flow. (correct)
How does boundary layer thickness change with distance from the leading edge?
How does boundary layer thickness change with distance from the leading edge?
What role does Reynolds number play in fluid flow?
What role does Reynolds number play in fluid flow?
What happens to the velocity of fluid in the boundary layer as it flows over a solid body?
What happens to the velocity of fluid in the boundary layer as it flows over a solid body?
What is the primary consequence of boundary layer separation?
What is the primary consequence of boundary layer separation?
At what point on a solid body does the boundary layer begin to separate?
At what point on a solid body does the boundary layer begin to separate?
Which method is NOT mentioned as a way to prevent boundary layer separation?
Which method is NOT mentioned as a way to prevent boundary layer separation?
What is one effect of the loss of kinetic energy in the boundary layer?
What is one effect of the loss of kinetic energy in the boundary layer?
Which action is effective for energizing the boundary layer to prevent separation?
Which action is effective for energizing the boundary layer to prevent separation?
What characterizes the boundary layer when it separates?
What characterizes the boundary layer when it separates?
Which of the following is a correct definition for the term 'boundary layer'?
Which of the following is a correct definition for the term 'boundary layer'?
Which characteristic distinguishes a turbulent boundary layer from a laminar boundary layer?
Which characteristic distinguishes a turbulent boundary layer from a laminar boundary layer?
What happens to boundary layer thickness as the distance from the leading edge increases?
What happens to boundary layer thickness as the distance from the leading edge increases?
How does surface roughness influence the flow characteristics within a boundary layer?
How does surface roughness influence the flow characteristics within a boundary layer?
In which scenario is a laminar boundary layer more likely to occur?
In which scenario is a laminar boundary layer more likely to occur?
What is the relationship between Reynolds number and the stability of the boundary layer?
What is the relationship between Reynolds number and the stability of the boundary layer?
Flashcards
No-slip condition
No-slip condition
Fluid particles at a solid surface have zero velocity.
Laminar Boundary Layer
Laminar Boundary Layer
Smooth, parallel fluid flow with low skin friction.
Turbulent Boundary Layer
Turbulent Boundary Layer
Chaotic flow with eddies and high skin friction.
Reynolds number
Reynolds number
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Boundary Layer Thickness
Boundary Layer Thickness
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Boundary Layer
Boundary Layer
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Boundary Layer Separation
Boundary Layer Separation
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Point of Separation
Point of Separation
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Suction slot method
Suction slot method
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Additional energy method
Additional energy method
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Divergence method
Divergence method
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Guide blades
Guide blades
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Trip wires
Trip wires
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Study Notes
Boundary Layer Separation
- A boundary layer forms adjacent to a solid body immersed in a fluid flow
- Velocity within the layer varies from zero at the surface to free-stream velocity
- Boundary layer thickness increases along the body
- Fluid near surface loses kinetic energy due to friction, recovered via momentum exchange from adjacent layers
- Velocity decreases as one moves along the body
- Boundary layer separation occurs when it can't overcome surface resistance
- Separation point is the point where separation is imminent
Preventing Boundary Layer Separation
- Separation leads to backflow and energy loss
- Techniques to prevent separation:
- Suction of slow-moving fluid
- Energy addition from a blower
- Bypassing in slotted wings
- Rotating the boundary layer in the flow direction
- Providing slight divergence in diffusers
- Using guide blades in bends
- Using trip wires in laminar flow regions (e.g., over a sphere)
What is a Boundary Layer?
- Fluid particles at a solid surface adhere due to viscosity
- Boundary layer velocity increases from zero at surface to free-stream velocity
Key Boundary Layer Characteristics
- No-slip condition: Fluid velocity is zero at surface
- Velocity gradient: Velocity increases rapidly within boundary layer
- Thickness: Layer thickness increases along the body
Types of Boundary Layers
- Laminar Boundary Layer:
- Smooth, parallel fluid flow
- Lower Reynolds numbers
- Lower skin friction drag
- Less stable (prone to transition to turbulent)
- Turbulent Boundary Layer:
- Chaotic and irregular flow
- Higher Reynolds numbers
- Higher skin friction drag
- More stable (less prone to separation)
Transition from Laminar to Turbulent
- Transition depends on factors:
- Reynolds number: Ratio of inertial forces to viscous forces
- Surface roughness: Roughness promotes turbulence
- Pressure gradient: Adverse pressure gradients trigger transition
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