# Laminar flow

**laminarlaminar-flowlaminar air flowlaminar airflowattached airflowbasic stateflows smoothlyfluid laminar flowlaminalaminar characteristics**

In fluid dynamics, laminar flow is characterized by fluid particles following smooth paths in layers, with each layer moving smoothly past the adjacent layers with little or no mixing.wikipedia

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### Turbulence

**turbulentturbulent flowatmospheric turbulence**

When a fluid is flowing through a closed channel such as a pipe or between two flat plates, either of two types of flow may occur depending on the velocity and viscosity of the fluid: laminar flow or turbulent flow.

It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between those layers.

### Fluid dynamics

**hydrodynamicshydrodynamicfluid flow**

In fluid dynamics, laminar flow is characterized by fluid particles following smooth paths in layers, with each layer moving smoothly past the adjacent layers with little or no mixing.

Flow in which turbulence is not exhibited is called laminar.

### Eddy (fluid dynamics)

**eddieseddyswirl**

There are no cross-currents perpendicular to the direction of flow, nor eddies or swirls of fluids.

The transition from laminar to turbulent flow in a fluid is defined by the critical Reynolds number, for a closed pipe this works out to approximately

### Reynolds number

**ReynoldsReynolds numbersRe**

The velocity is determined by a dimensionless parameter characterizing the flow called the Reynolds' number, which also depends on the viscosity and density of the fluid and dimensions of the channel. The dimensionless Reynolds number is an important parameter in the equations that describe whether fully developed flow conditions lead to laminar or turbulent flow.

With respect to laminar and turbulent flow regimes:

### Laminar–turbulent transition

**boundary layer transitionlaminar to turbulentlaminar-turbulent boundary layer transition**

As the Reynolds number increases, such as by increasing the flow rate of the fluid, the flow will transition from laminar to turbulent flow at a specific range of Reynolds numbers, the laminar–turbulent transition range depending on small disturbance levels in the fluid or imperfections in the flow system.

The process of a laminar flow becoming turbulent is known as laminar–turbulent transition.

### Stokes flow

**creeping flowStokes equationsStokes equation**

If the Reynolds number is very small, much less than 1, then the fluid will exhibit Stokes, or creeping, flow, where the viscous forces of the fluid dominate the inertial forces.

The cylinders are rotated relative to one another at a low speed, which together with the high viscosity of the fluid and thinness of the gap gives a low Reynolds number, so that the apparent mixing of colors is actually laminar and can then be reversed to approximately the initial state.

### Shear stress

**shearshearingwall shear stress**

The Reynolds number is the ratio of the inertial force to the shearing force of the fluid: how fast the fluid is moving relative to how viscous it is, irrespective of the scale of the fluid system.

For all Newtonian fluids in laminar flow, the shear stress is proportional to the strain rate in the fluid, where the viscosity is the constant of proportionality.

### Laminar flow cabinet

**laminar flow hoodsflowboxbiological safety cabinets**

Laminar flow hoods are used to exclude contaminants from sensitive processes in science, electronics and medicine.

Air is drawn through a HEPA filter and blown in a very smooth, laminar flow towards the user.

### Laminar flow reactor

A laminar flow reactor (LFR) is a reactor that uses laminar flow to study chemical reactions and process mechanisms.

A laminar flow reactor (LFR) is a type of chemical reactor that uses laminar flow to control reaction rate, and/or reaction distribution.

### Boundary layer

**boundary layersboundary layer theoryboundary-layer**

The boundary layer is a very thin sheet of air lying over the surface of the wing (and all other surfaces of the aircraft).

At high Reynolds numbers, typical of full-sized aircraft, it is desirable to have a laminar boundary layer.

### Chemical reactor

**reactorreactorschemical reactors**

A laminar flow reactor (LFR) is a reactor that uses laminar flow to study chemical reactions and process mechanisms.

Under laminar flow conditions, the assumption of plug flow is highly inaccurate, as the fluid traveling through the center of the tube moves much faster than the fluid at the wall.

### Convection

**convectiveconvection currentsconvection current**

Laminar flow is a flow regime characterized by high momentum diffusion and low momentum convection.

### Heat transfer

**heat flowheatheat exchange**

The type of flow occurring in a fluid in a channel is important in fluid-dynamics problems and subsequently affects heat and mass transfer in fluid systems.

### Mass transfer

**massmass transporttransfer of mass**

The type of flow occurring in a fluid in a channel is important in fluid-dynamics problems and subsequently affects heat and mass transfer in fluid systems.

### Dimensionless quantity

**dimensionlessdimensionless numberdimensionless quantities**

The dimensionless Reynolds number is an important parameter in the equations that describe whether fully developed flow conditions lead to laminar or turbulent flow.

### Fictitious force

**inertial forcefictitious forcesinertial**

The Reynolds number is the ratio of the inertial force to the shearing force of the fluid: how fast the fluid is moving relative to how viscous it is, irrespective of the scale of the fluid system.

### Flow conditioning

**flow conditionflow conditionersflow in a pipe**

The common example is flow through a pipe, where the Reynolds number is defined as

### Hydraulic diameter

**wetted area**

is the hydraulic diameter of the pipe (m);

### Volumetric flow rate

**flow rateflowvolume flow rate**

is the volumetric flow rate (m 3 /s);

### International System of Units

**SISI unitsSI unit**

is the mean speed of the fluid (SI units: m/s);

### Viscosity

**viscouskinematic viscositydynamic viscosity**

The Reynolds number is the ratio of the inertial force to the shearing force of the fluid: how fast the fluid is moving relative to how viscous it is, irrespective of the scale of the fluid system.

### Density

**densemass densitydensities**

is the density of the fluid (kg/m 3 ).

### Vortex shedding

**sheddingcreating and shedding vorticesScruton strake**

As with flow in pipes, laminar flow typically occurs with lower Reynolds numbers, while turbulent flow and related phenomena, such as vortex shedding, occur with higher Reynolds numbers.