Name: linear shear between moving plates
Uploaded: 2025-02-13T15:43:26.000Z
Duration: 1 min 22 s
Channel: JoVE

Il flusso di Couette descrive il movimento del fluido tra due piastre parallele in cui una è ferma e l'altra si muove a velocità costante, creando un flusso costante guidato dal taglio laminare.
Questa configurazione semplifica le equazioni di Navier-Stokes, che possono essere espresse in forma adimensionale.
Un parametro adimensionale, relativo al gradiente di pressione, definisce le variazioni nei profili di flusso di Couette.
Quando non c'è gradiente di pressione lungo la direzione del flusso, questo parametro diventa zero, indicando una variazione di velocità lineare tra le due piastre.
Il profilo di velocità del fluido tra le piastre è lineare, aumentando da zero sulla piastra stazionaria alla velocità della piastra in movimento.
Il flusso Couette è comunemente usato per modellare il comportamento dei fluidi in cuscinetti portanti leggermente caricati, come quelli delle pompe dell'acqua, dove un sottile strato di lubrificante separa un albero rotante all'interno di un alloggiamento fisso.
In questi cuscinetti leggermente caricati, gli effetti della pressione sono minimi, quindi le caratteristiche di flusso sono molto simili a quelle del flusso di Couette puro.
La sollecitazione di taglio e la portata dello strato di lubrificante dipendono dalla velocità di rotazione dell'albero e dalla larghezza della fessura tra l'albero e l'alloggiamento.

flusso di couette

Couette Flow

Il flusso di Couette rappresenta il flusso di fluido tra due piastre parallele, con una piastra stazionaria e l'altra in movimento a velocità costante. Questa configurazione consente un'analisi semplificata, utilizzando le equazioni di Navier-Stokes, che regolano il movimento del fluido in condizioni di viscosità e incomprimibilità. Per il flusso di Couette, le ipotesi includono un flusso stazionario, laminare, incomprimibile, con un gradiente di pressione zero nella direzione del flusso. Questo tipo di flusso, è utile per comprendere i flussi guidati dal taglio ed è rilevante per le applicazioni in scenari di lubrificazione e ingegneria civile, come il trasporto di sedimenti e l'erosione.

In una configurazione di flusso di Couette, si lascia che l'asse x si allinei con la direzione di movimento della piastra superiore mentre l'asse y è perpendicolare a entrambe le piastre. Il flusso è costante, laminare e completamente sviluppato, senza variazioni nel

Per il flusso di Couette, l'equazione di distribuzione della velocità è data da:

<img alt="Equation 1" src="/files/ftp_upload/18064/18064_Equation_1.svg" style="text-align: center; height: 30px;">

Dove:

<ul style="list-style-type: disc; display: flex; flex-direction: column; gap: 10px; padding: 0 0 0 40px;">
 <li>U è la velocità costante della piastra superiore,</li>
 <li>b è la distanza tra le piastre,</li>
 <li>μ è la viscosità dinamica del fluido.</li>
</ul>

In forma adimensionale, dividendo entrambi i lati per U, otteniamo:

<img alt="Equation 2" src="/files/ftp_upload/18064/18064_Equation_2.svg" style="text-align: center; height: 30px;">

Dove u/U rappresenta la velocità adimensionale e y/b rappresenta la distanza normalizzata dalla piastra stazionaria. Per analizzare condizioni specifiche, definiamo il parametro adimensionale P come:

<img alt="Equation 3" src="/files/ftp_upload/18064/18064_Equation_3.svg" style="text-align: center; height: 30px;">

In queste condizioni, P si annulla quando non c'è gradiente di pressione (∂p/∂x=0) nella direzione x, riducendo l'equazione della velocità a:

<img alt="Equation 4" src="/files/ftp_upload/18064/18064_Equation_4.svg" style="text-align: center; height: 26px;">

Questo profilo lineare indica che la velocità del fluido aumenta linearmente da zero sulla piastra stazionaria a U sulla piastra mobile, con conseguente velocità di taglio uniforme attraverso lo strato di fluido.

Flusso di Couette

Il flusso di Couette descrive il movimento del fluido tra due piastre parallele in cui una è ferma e l'altra si muove a velocità costante, creando un movimento ...

Education

Didattica

JoVE Core

Civil Engineering

Ingegneria Civile

Unit 1

Unità 1

Differential Analysis of Fluid Flow

Analisi differenziale del flusso di fluidi

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

linear shear between moving plates

Linear shear between moving plates describes fluid motion in a simple channel with two parallel plates. One plate stays fixed, and the other moves at a constant speed. This setup helps show how viscosity and incompressible flow shape fluid motion under the Navier-Stokes equations.

The model uses a steady, laminar, incompressible flow with no pressure gradient in the flow direction. The x-axis points along the moving direction of the upper plate, and the y-axis is perpendicular to both plates. These assumptions make the flow fully developed and easier to analyze.

For this case, the velocity changes with distance from the stationary plate. The upper plate speed is U, the plate spacing is b, and the fluid’s dynamic viscosity is μ. In dimensionless form, the velocity is written as u/U, and the position is written as y/b.

A dimensionless parameter P is used to describe pressure effects. When there is no pressure gradient in the x-direction, P becomes zero because ∂p/∂x = 0. The velocity equation then reduces to a straight line, so the fluid speed rises from zero at the fixed plate to U at the moving plate.

This linear profile creates a uniform shear rate across the fluid layer. Shear-driven flow like this is useful for understanding lubrication and civil engineering problems. It also helps explain processes such as sediment transport and erosion.

Linear Shear Between Moving Plates

euler&#39;s equations of motion

Pressure and Velocity in Inviscid Flow

Pressure and velocity in inviscid flow are linked by Euler's equations of motion. In fluid mechanics, viscosity creates shear stress, which is a force that acts along a surface. For low-viscosity fluids like water, these shear stresses are very small. That lets the fluid be treated as inviscid, or frictionless. In an inviscid fluid, shear stresses are absent. Only normal stresses remain, and these act perpendicular to a fluid element. Pressure is the negative of the normal stress. It stays the...

stream function

Stream Function for Incompressible Flow

The stream function helps describe two-dimensional incompressible flow. In this type of flow, the continuity equation keeps mass conserved. That means fluid entering a region must be balanced by fluid leaving it. For incompressible flow, the density stays constant. The continuity requirement then becomes a zero-divergence condition for the velocity field. In two dimensions, the horizontal and vertical velocity components are usually written as u and v. A stream function, written as ψ, is used...

irrotational flow

Irrotational Flow Near Boundaries

Irrotational flow is fluid motion in which particles do not spin around their own axes. It has zero vorticity, which means the curl of the velocity field is zero. That condition places limits on the velocity gradients in the flow. A simple example is uniform flow. In this case, the velocity u stays constant, while v and w are both zero. This satisfies the irrotational conditions and gives a basic model of non-rotating flow. When a solid object is added, irrotational flow usually remains only...

velocity potential

Velocity Potential in Pipe Flow

Velocity potential in pipe flow describes the motion of fluid in the central region of a long, straight pipe with a uniform cross-section. In this region, the flow is steady, incompressible, and irrotational. Irrotational means the fluid particles do not spin around their own axes. A scalar function called the velocity potential, written as φ, is used to describe this motion. The velocity field V is defined as the gradient of φ. Because the curl of a gradient is always zero, this form of V...

plane potential flows

Plane Potential Flow Patterns and Models

Plane potential flows describe fluid motion using simple flow patterns and models. They assume the fluid is irrotational and incompressible. These assumptions let the flow be written with a velocity potential function, φ, which gives the flow speed in a direction, and a stream function, ψ, which shows the flow path. Both are governed by Laplace's equation and are useful for estimating flow patterns, velocity distributions, and pressure fields around hydraulic structures. Uniform flow is the...

navier&#8211;stokes equations

Fluid Stress and Flow Equations

Fluid stress and flow equations describe how incompressible Newtonian fluids move under pressure, shear, and gravity. In these fluids, density stays constant, and stress changes linearly with the rate of deformation. The main stress types are normal stress and shear stress. Normal stress depends on pressure acting on the fluid and on deformation rate in specific directions. Shear stress acts along the surface of a fluid layer. It shows how neighboring layers slide past one another, so velocity...

steady, laminar flow between parallel plates

steady-laminar-flow-between-parallel-plates

Laminar Flow Profile Between Parallel Plates

Laminar flow between parallel plates shows how fluid moves through a narrow, flat channel. This model helps describe flow in water conveyance and drainage systems, where the space is limited and the motion stays orderly. It is also useful for analyzing flow in rectangular channels used in many engineering settings. The flow is studied with the Navier-Stokes equations, which govern fluid motion. These equations are often difficult to solve because they are nonlinear. In this case, the problem...

couette flow

Linear shear between moving plates describes fluid motion in a simple channel with two parallel plates. One plate stays fixed, and the other moves at a constant speed. This setup helps show how viscosity and incompressible flow shape fluid motion under the Navier-Stokes equations. The model uses a steady, laminar, incompressible flow with no pressure gradient in the flow direction. The x-axis points along the moving direction of the upper plate, and the y-axis is perpendicular to both plates.

steady, laminar flow in circular tubes

Parabolic Flow in Circular Tubes

Parabolic flow in circular tubes describes the steady, incompressible motion of a viscous fluid through a tube with a constant radius. This Hagen-Poiseuille flow is a classic example of laminar flow. It is often used to study fluid transport in narrow channels, including capillaries. Cylindrical coordinates are used to describe the tube. The radial direction is r, the angular direction is θ, and the axial direction is z. In this flow, the velocity is purely axial. That means the fluid moves...

design example: flow of oil through circular pipes

design-example-flow-of-oil-through-circular-pipes

Pressure Drop in Oil Pipe Design

Pressure drop in oil pipe design depends on pipe size, oil properties, and the flow rate needed through a circular pipe. For steady, incompressible, laminar flow, Hagen-Poiseuille's law gives an exact solution from the Navier-Stokes equations. It is used to find the pressure difference needed to keep oil moving through a pipeline section. The pressure drop equation uses the oil's dynamic viscosity, the pipeline length, the desired volumetric flow rate, and the pipe's inner radius. This...

key terms and concepts

Learn how fluid moves between two parallel plates when one plate is fixed and the other moves. See the linear velocity profile, shear rate, and key assumptions.

Linear Shear Between Moving Plates | JoVE K12

JoVE Core Civil Engineering provides a foundational exploration of essential construction materials in civil engineering, focusing on bricks, stones, steel, wood, and concrete through easy-to-understand animated videos. This collection covers the properties, manufacturing processes, and practical applications of these materials. Additionally, the accompanied science-in-action videos demonstrate the research experiments performed in laboratories.

civil engineering

Linear Shear Between Moving Plates

Description

Transcript

Tags