Turbulent Flow is MORE Awesome Than Laminar Flow

Veritasium
11 Jun 202018:32
EducationalLearning
32 Likes 10 Comments

TLDRThe video script explores the contrasting characteristics of laminar and turbulent flow, highlighting the unpredictability and complexity of turbulent flow. It delves into the Reynolds number as a determinant of flow type and the practical implications of turbulence in various real-world scenarios, such as airplane flight and golf ball aerodynamics. The script also touches on the environmental impact of turbulent wakes and the potential for harnessing their energy, emphasizing the ubiquity and significance of turbulence in our world.

Takeaways
  • 🌀 Laminar flow is characterized by fluid particles moving in parallel layers, while turbulent flow is unpredictable and chaotic.
  • 🔍 There is no universally agreed-upon definition of turbulent flow, but it is recognized by its complex, swirling motion.
  • 📈 Turbulent flow is sensitive to initial conditions, making it difficult to predict and often described statistically.
  • 🌟 Turbulence is diffusive, leading to the mixing of substances like dye, heat, or momentum throughout a fluid.
  • 🚀 High Reynolds numbers, which account for fluid velocity, characteristic length, and kinematic viscosity, result in turbulent flow.
  • 💨 Turbulent flow is common in everyday life, including the air we breathe and the blood pumping through our bodies.
  • 🛫 Aircraft design often incorporates elements to induce turbulence to delay stall and improve flight efficiency.
  • 🏌️ Golf balls utilize dimples to create a turbulent boundary layer, reducing drag and allowing them to travel further.
  • 🌪️ Vortex shedding, like the von Karman Vortex Street, is a phenomenon where vortices are shed alternately from opposite sides of an object, contributing to turbulence.
  • 🧪 Experiments with flushable wipes demonstrate their ability to break down after use, emphasizing the importance of proper disposal to prevent sewer blockages.
Q & A

  • What is the main difference between laminar and turbulent flow?

    -Laminar flow is characterized by fluid particles moving in parallel layers, while turbulent flow involves chaotic and unpredictable motion with many interacting swirls or eddies of fluid.

  • How does Chris Hadfield describe the flow in the space station?

    -Chris Hadfield describes the flow in the space station as largely laminar, not turbulent, indicating an organized and smooth movement of fluids.

  • What is a defining characteristic of turbulent flow?

    -A defining characteristic of turbulent flow is its unpredictability. It is sensitively dependent on initial conditions, making it difficult to predict and often requiring statistical analysis.

  • What is the significance of the Reynolds number in fluid dynamics?

    -The Reynolds number is a dimensionless quantity that predicts the onset of turbulence. It is calculated based on the fluid's velocity, a characteristic length (like pipe diameter), and its kinematic viscosity. High Reynolds numbers result in turbulent flow.

  • How does turbulent flow affect objects moving through a fluid?

    -Turbulent flow increases skin friction and drag on objects moving through a fluid due to the chaotic and swirling motion of the fluid. This can be mitigated by maintaining a laminar boundary layer, which is more efficient.

  • What is the role of turbulence in the formation of raindrops?

    -Turbulence plays an essential role in the formation of raindrops. It helps mix things together, including water vapor and heat, which contributes to the condensation and coalescence of droplets that form rain.

  • How do vortex generators on an airplane wing contribute to preventing stall?

    -Vortex generators induce turbulence on the wing's surface, which energizes the airflow and helps it follow the wing's curve even at higher angles of attack. This delays flow separation and stall, maintaining lift and allowing the plane to fly efficiently.

  • What is the impact of a golf ball's dimples on its flight?

    -Dimples on a golf ball create a turbulent boundary layer, which reduces pressure drag by delaying the separation of airflow from the ball's surface. This allows the ball to travel further with less drag.

  • How do fish utilize turbulent water to swim more efficiently?

    -Fish can take advantage of the energy in turbulent water to swim more efficiently. Experiments have shown that fish can use the vortices created by turbulent flow to swim upstream without expending much energy.

  • What is the von Karman Vortex Street and where can it be observed?

    -The von Karman Vortex Street is a pattern of alternating vortices shed by an object in a fluid, creating a regular, predictable pattern. It can be observed in large-scale phenomena like the swirling cloud patterns around an island and even in small-scale experiments in a laboratory.

  • What is the main issue with flushing baby wipes down the toilet?

    -Baby wipes do not break down as easily as flushable wipes, leading to blockages in the sewer system. Flushing baby wipes is a common cause of sewer backups and is discouraged to prevent plumbing issues.

Outlines
00:00
🌀 The Debate of Laminar vs Turbulent Flow

This paragraph introduces the contrast between laminar and turbulent flow, highlighting a debate between the narrator and Destin from Smarter Every Day. The discussion revolves around the characteristics of laminar flow, which is orderly and parallel, versus turbulent flow, which is chaotic and unpredictable. The narrator argues that while laminar flow is visually appealing, turbulent flow is more fascinating and complex, despite its lack of a universally accepted definition. The paragraph sets the stage for a deeper exploration of turbulent flow and its significance in various phenomena, from the microscale to the cosmic scale.

05:01
💨 Understanding Turbulent Flow: Characteristics and Examples

The second paragraph delves into the properties of turbulent flow, emphasizing its unpredictability and diffusivity. It explains how turbulent flow is sensitive to initial conditions and how this leads to a lack of predictability, with the Navier-Stokes equations being difficult to solve due to this complexity. The paragraph also discusses the Reynolds number, which is a measure used to predict the onset of turbulence. It provides examples of turbulence in everyday life, such as the air flowing in and out of lungs and the formation of raindrops, and contrasts this with laminar flow, which is limited to low speeds, small sizes, or viscous fluids.

10:04
🛫 Applications of Turbulence in Engineering and Nature

This paragraph explores the practical applications and natural occurrences of turbulence. It discusses how turbulence is induced on airplane wings through vortex generators to delay stall and maintain lift, and how golf balls utilize turbulence to reduce drag and fly further. The paragraph also touches on the concept of harnessing the energy within turbulent wakes and the phenomenon of von Karman Vortex Street, which is observed in various scales, from small-scale experiments to large-scale natural occurrences like cloud patterns around islands.

15:07
🌿 Turbulence in Everyday Life and Its Environmental Impact

The final paragraph brings the discussion back to everyday experiences, emphasizing that while laminar flow is often seen as a symbol of order, turbulence is the norm in the natural world and has significant uses. It also addresses the environmental impact of flushing non-flushable items like baby wipes, which can cause severe blockages in sewer systems. The narrator shares a personal anecdote about a sewer backup caused by baby wipes and presents an experiment comparing the flushability of different wipes, concluding with a recommendation for Cottonelle flushable wipes due to their ability to break down after flushing.

Mindmap
Keywords
💡Laminar Flow
Laminar flow refers to a smooth, orderly, and predictable flow of a fluid where particles move in parallel layers or laminae. In the video, it is contrasted with turbulent flow, with the speaker arguing that while laminar flow is visually appealing and well-behaved, it is not as fascinating or complex as turbulent flow. An example given is the steady stream of dye in a pipe at low flow rates, which remains unmixed and orderly, representing laminar flow.
💡Turbulent Flow
Turbulent flow is characterized by chaotic, unpredictable, and disordered fluid motion with swirling eddies and vortices. The video emphasizes that turbulent flow is more complex and fascinating than laminar flow, despite its messiness. It is described as being sensitive to initial conditions, leading to the inability to make precise predictions about its behavior. The video also mentions that turbulent flow is diffusive, meaning it mixes substances like heat or momentum throughout the fluid.
💡Eddies
Eddies are small, rotating currents within a fluid, and they are a defining characteristic of turbulent flow. The video describes eddies as interacting swirls of fluid that can span a wide range of sizes, from micrometers to meters in diameter, and even larger in cosmic scales. Eddies contribute to the chaotic and unpredictable nature of turbulent flow and are responsible for the mixing and diffusion of substances within the fluid.
💡Reynolds Number
The Reynolds number is a dimensionless quantity used to predict the onset of turbulence in fluid flow. It is calculated by dividing the product of the fluid's velocity and a characteristic length (such as the pipe diameter) by the fluid's kinematic viscosity. High Reynolds numbers are associated with turbulent flow, while low Reynolds numbers indicate laminar flow. The video uses the Reynolds number to explain the transition from laminar to turbulent flow under different conditions, such as flow rate and pipe width.
💡Boundary Layer
A boundary layer is the region of fluid that is affected by the surface over which it flows. In the video, it is explained that a laminar boundary layer forms when the fluid velocity increases from zero at the surface to the free stream velocity away from the surface. This layer can become turbulent under certain conditions, such as high fluid velocity or surface roughness, leading to increased skin friction and drag. The video also discusses how turbulence in boundary layers can be beneficial, such as in delaying flow separation on airplane wings.
💡Vortex Generators
Vortex generators are small devices or features designed to intentionally create turbulence in fluid flow. In the context of the video, they are used on airplane wings to delay flow separation and stall by energizing the boundary layer. By introducing turbulence, the vortex generators mix faster flowing air closer to the surface, allowing the air to follow the wing's curve more effectively and maintain lift. This concept is also applied to golf balls, where dimples act as natural vortex generators to improve their aerodynamic performance.
💡Von Karman Vortex Street
The von Karman vortex street is a pattern of alternating vortices that form behind an object in a fluid, such as a cylinder. This phenomenon is an example of periodic vortex shedding and is part of the transition to turbulence. The video mentions that these patterns are visible in various scales, from small-scale experiments to large-scale atmospheric phenomena, and that scientists are interested in harnessing the energy contained within these vortex structures.
💡Skin Friction
Skin friction is the drag force experienced by a fluid as it moves over a surface due to the friction between the fluid and the surface molecules. In the video, it is discussed in the context of boundary layers, where a laminar boundary layer has less skin friction than a turbulent one. The transition from laminar to turbulent flow in a boundary layer significantly increases skin friction, which in turn increases drag on objects like airplanes and cars.
💡Pressure Drag
Pressure drag is a form of drag experienced by an object due to pressure differences in the fluid flow around it. In the video, it is explained that a smooth, laminar boundary layer on an object like a golf ball can lead to low skin friction but also to easy separation of the flow, resulting in a large wake and high pressure drag. By introducing turbulence through dimples or roughness, the boundary layer can remain attached longer, reducing the wake and pressure drag, which allows the golf ball to travel further.
💡Cosmic Turbulence
Cosmic turbulence refers to the turbulent motion of fluids on a cosmic scale, such as the dust between stars or the plasma on the surface of the Sun. The video highlights that turbulence is not limited to small scales and can be observed in structures as large as the Orion Nebula, which is twenty-four light years across, and even larger, like the Great Red Spot on Jupiter, which is bigger than Earth.
💡Flushable Wipes
Flushable wipes are a type of personal hygiene product designed to break down and disperse in water after use, allowing them to be flushed down toilets. In the video, an experiment is conducted to test the flushability of Cottonelle flushable wipes compared to non-flushable baby wipes and paper towels. The results show that the flushable wipes break down after being submerged in water, which is essential to prevent sewer blockages and maintain plumbing systems.
Highlights

Laminar flow is characterized by fluid particles moving in parallel layers, while turbulent flow is more chaotic and unpredictable.

Turbulent flow is not better than laminar flow, but it is equally awesome in its own right.

Turbulent flow is sensitive to initial conditions and is defined by its unpredictability.

The Navier-Stokes equations govern fluid flow, including turbulence, but are notoriously difficult to solve.

There is a million-dollar prize for progress in understanding the Navier-Stokes equations and explaining turbulence.

Turbulent flow consists of many interacting swirls of fluid called eddies or vortices, spanning a wide range of sizes.

Turbulence is a universal phenomenon, observed from the surface of the Sun to the dust between stars.

Laminar flow is typically small-scale and requires low flow rates, low speeds, or viscous fluids.

Turbulent flow is diffusive, meaning it mixes things together, spreading out substances like dye, heat, or momentum throughout the fluid.

The Reynolds number, a dimensionless quantity, is used to predict the onset of turbulence based on flow rate, pipe diameter, and fluid viscosity.

Turbulence is dissipative, requiring a constant source of energy to maintain the large eddies that drive the flow.

Boundary layers form where fluid velocity changes from zero at the surface to the free stream velocity, with laminar boundary layers transitioning to turbulent under certain conditions.

Turbulent boundary layers increase skin friction, leading to more drag on objects moving through a fluid, such as planes and ships.

Vortex generators on airplane wings induce turbulence to delay flow separation and stall, improving flight efficiency.

Golf balls with dimples create a turbulent boundary layer, reducing pressure drag and allowing them to travel further.

Von Karman Vortex Street, a pattern of periodic vortex shedding, is a visual representation of the transition to turbulence and has potential energy harnessing applications.

Turbulence is a fundamental aspect of the natural world, influencing phenomena from rain formation to the flight of airplanes and the movement of fish.

Laminar flow, while aesthetically pleasing, is less common in nature and often used for decorative purposes like fountains.

The video was filmed before the COVID outbreak, and the sponsor, Cottonelle, has been working to restock their flushable wipes.

Cottonelle flushable wipes break down after flushing, unlike baby wipes, which can cause sewer blockages.

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Fluid DynamicsTurbulenceLaminar FlowChris HadfieldDestinPhysicsSpace StationNavier-StokesReynolds NumberAerodynamicsMythbustersVortex GeneratorsGolf Ball AerodynamicsTurbulence ApplicationsRocket NozzlesEnvironmental ImpactCottonelle WipesSewer SystemsProduct Testing