Onset Of Turbulence Quiz: Test Fluid Flow Transition Physics

Grade 9th

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| Attempts: 11 | Questions: 20 | Updated: Mar 13, 2026

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1. At low Reynolds number, flow is usually:

Laminar

Always turbulent

Always compressible

Always supersonic

Concept: low Re regime. When viscosity dominates, it smooths out fluctuations quickly. This supports steady, layered laminar motion.

Explanation

Concept: low Re regime. When viscosity dominates, it smooths out fluctuations quickly. This supports steady, layered laminar motion.

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About This Quiz

Onset Of Turbulence Quiz: Test Fluid Flow Transition Physics - Quiz

This assessment explores the concept of turbulence, focusing on its triggers and implications in aerospace contexts. It evaluates knowledge of key principles such as airflow dynamics, pressure variations, and their effects on aircraft performance. Understanding turbulence is crucial for pilots, engineers, and aviation professionals to enhance safety and efficiency in... see moreflight operations. see less

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2. Transition to turbulence can happen at different speeds depending on the pipe roughness and inlet disturbances.

True

False

Concept: sensitivity of transition. Real transition thresholds depend on how disturbed the flow is and the surface condition. Roughness and upstream disturbances can cause earlier turbulence.

Explanation

Concept: sensitivity of transition. Real transition thresholds depend on how disturbed the flow is and the surface condition. Roughness and upstream disturbances can cause earlier turbulence.

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3. Which situation is most likely to stay laminar?

High-speed air around a racing car

Whitewater rapids

Very slow flow of oil in a thin capillary

A fast jet from a nozzle

Concept: low Re conditions. Small length scales and low speeds reduce Reynolds number. Higher viscosity also helps keep the flow laminar.

Explanation

Concept: low Re conditions. Small length scales and low speeds reduce Reynolds number. Higher viscosity also helps keep the flow laminar.

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4. Reynolds number is often written as Re and is ______ (has no units).

Concept: dimensionless ratio. Reynolds number is a pure ratio comparing effects, so units cancel. That makes it useful for comparing different flows.

Explanation

Concept: dimensionless ratio. Reynolds number is a pure ratio comparing effects, so units cancel. That makes it useful for comparing different flows.

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5. A key outcome of turbulence in pipelines is often:

Zero pressure drop

Increased frictional pressure loss

No mixing

Constant velocity everywhere

Concept: turbulent losses. Turbulence enhances momentum exchange, increasing effective friction. This often raises pressure drop compared with laminar flow for similar conditions.

Explanation

Concept: turbulent losses. Turbulence enhances momentum exchange, increasing effective friction. This often raises pressure drop compared with laminar flow for similar conditions.

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6. Turbulence can occur at many different scales, from small eddies to large swirls.

True

False

Concept: multiscale structure. Turbulence includes a range of eddy sizes. Larger eddies break into smaller ones, transferring energy across scales.

Explanation

Concept: multiscale structure. Turbulence includes a range of eddy sizes. Larger eddies break into smaller ones, transferring energy across scales.

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7. Which change tends to make flow more laminar?

Increasing speed

Increasing pipe diameter

Increasing viscosity

Adding obstacles

Concept: stabilising factors. Higher viscosity damps disturbances and lowers Reynolds number. Obstacles and high speed generally promote turbulence instead.

Explanation

Concept: stabilising factors. Higher viscosity damps disturbances and lowers Reynolds number. Obstacles and high speed generally promote turbulence instead.

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8. Turbulence is often strongest near ______ where velocity gradients are large.

Concept: near-wall turbulence. The no-slip condition creates steep velocity gradients near walls. These gradients generate shear and can sustain turbulence.

Explanation

Concept: near-wall turbulence. The no-slip condition creates steep velocity gradients near walls. These gradients generate shear and can sustain turbulence.

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9. If you double the flow speed in the same pipe with the same fluid, Reynolds number:

Halves

Doubles

Stays the same

Becomes zero

Concept: proportionality to speed. Reynolds number is proportional to speed when other factors are fixed. Increasing speed increases the inertia-to-viscosity ratio.

Explanation

Concept: proportionality to speed. Reynolds number is proportional to speed when other factors are fixed. Increasing speed increases the inertia-to-viscosity ratio.

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10. Reynolds number depends on speed, a length scale, and fluid properties.

True

False

Concept: inputs to Re. Re increases with speed and characteristic length and decreases with viscosity (or increases with lower kinematic viscosity). That’s why both geometry and fluid type matter.

Explanation

Concept: inputs to Re. Re increases with speed and characteristic length and decreases with viscosity (or increases with lower kinematic viscosity). That’s why both geometry and fluid type matter.

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11. Turbulence becomes more likely when:

Speed decreases a lot

Speed increases

The fluid stops moving

The container becomes lighter

Concept: inertia vs stability. Higher speed strengthens inertial effects that can amplify disturbances. This can destabilise smooth flow and promote turbulence.

Explanation

Concept: inertia vs stability. Higher speed strengthens inertial effects that can amplify disturbances. This can destabilise smooth flow and promote turbulence.

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12. In pipe flow, turbulence often starts because of:

Perfect symmetry forever

Small disturbances that get amplified

Zero viscosity

No shear near walls

Concept: instability growth. Real flows always have small disturbances from vibrations, roughness, or inlet conditions. If conditions favour growth, these disturbances lead to turbulence.

Explanation

Concept: instability growth. Real flows always have small disturbances from vibrations, roughness, or inlet conditions. If conditions favour growth, these disturbances lead to turbulence.

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13. Surface roughness can encourage turbulence by disturbing near-wall flow.

True

False

Concept: roughness effects. Roughness creates small perturbations and increases shear near the wall. This can trigger earlier transition and increase turbulence intensity.

Explanation

Concept: roughness effects. Roughness creates small perturbations and increases shear near the wall. This can trigger earlier transition and increase turbulence intensity.

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14. The change from laminar to turbulent flow is called the ______ to turbulence.

Concept: transition. Transition is when disturbances grow enough that the flow becomes chaotic and eddy-filled. It often depends on speed, geometry, and surface roughness.

Explanation

Concept: transition. Transition is when disturbances grow enough that the flow becomes chaotic and eddy-filled. It often depends on speed, geometry, and surface roughness.

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15. Which situation is most likely turbulent?

Slow glycerine flow in a thin tube

Fast water flow in a large pipe

Slow air in a sealed box

A still pond

Concept: Re and conditions. Fast flow and large size both raise Reynolds number, making turbulence more likely. Slow, viscous, small-scale flows are often laminar.

Explanation

Concept: Re and conditions. Fast flow and large size both raise Reynolds number, making turbulence more likely. Slow, viscous, small-scale flows are often laminar.

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16. A smooth, straight pipe can still have turbulence if the flow rate is high enough.

True

False

Concept: turbulence without obstacles. Even without obstacles, high-speed flow can become unstable due to shear and small disturbances. Beyond a certain regime, turbulence can sustain itself.

Explanation

Concept: turbulence without obstacles. Even without obstacles, high-speed flow can become unstable due to shear and small disturbances. Beyond a certain regime, turbulence can sustain itself.

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17. Which change would most likely increase Reynolds number (all else equal)?

Increasing viscosity

Decreasing speed

Increasing pipe diameter

Decreasing density

Concept: Re increases with size and speed. Reynolds number grows with characteristic length and speed and decreases with viscosity. A bigger pipe diameter tends to raise Re.

Explanation

Concept: Re increases with size and speed. Reynolds number grows with characteristic length and speed and decreases with viscosity. A bigger pipe diameter tends to raise Re.

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18. If Reynolds number increases, flow is generally more likely to become ______.

Concept: flow regime trend. Higher Reynolds number means inertia is relatively stronger. That makes disturbances more likely to grow into turbulence.

Explanation

Concept: flow regime trend. Higher Reynolds number means inertia is relatively stronger. That makes disturbances more likely to grow into turbulence.

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19. Reynolds number is mainly a comparison between:

Heat and temperature

Inertial effects and viscous effects

Mass and volume

Pressure and density only

Concept: Reynolds number meaning. Reynolds number estimates whether inertia (which can create instability) dominates over viscosity (which damps motion). Higher Reynolds number often corresponds to more turbulent behaviour.

Explanation

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