What is uniform flow and can uniform flow be divided into laminar flow and turbulent flow?

Taking space as the standard, that is, according to whether the motion element (mainly refers to the flow velocity) changes with the spatial position, the flow is divided into uniform flow and non-uniform flow. If the velocity of each point in the flow field does not change with the spatial position (including magnitude and direction), it is called uniform flow, otherwise it is non-uniform.

For a uniform flow, the magnitude and direction of the velocity of the liquid particle remain unchanged along the process, that is, the migration acceleration is zero, and the particle can only move in a uniform straight line along the streamline. The movement of water in a long straight channel or pipe with the shape and size of the cross-section and the boundary conditions unchanged along the course is considered a uniform flow.

The characteristics of uniform flow are: the streamlines are straight lines parallel to each other, and the flow velocity distribution on each section perpendicular to the streamline is the same, while the characteristics of non-uniform flow are opposite, not only the streamlines are not parallel to each other or the streamlines are bent, but also the flow velocity distribution on each section perpendicular to the streamline is also different.

If the moving features do not change with the coordinate position (flow) during the flow, the flow is called uniform flow.

Characteristics of uniform flow:

1) The streamlines of uniform flow are parallel to each other in straight lines, and the overflow section is flat, and the shape and size of the overflow section remain unchanged along the way.

2) In a uniform flow, the flow velocity at different points on the same flow line should be equal, so that the flow velocity distribution on each flow section is the same, and the average flow velocity of the section is equal, that is, the flow velocity remains unchanged along the route.

3) The distribution law of hydrodynamic pressure on the uniform flow section is the same as that of the hydrostatic pressure, that is, the head of the piezometer pipe at each point on the same flow section is a constant.

Summary. Hello, uniform flow can be divided into laminar flow and turbulent flow.

Hello, uniform flow can be divided into laminar flow and turbulent flow.

First of all, uniform flow refers to the flow that is called uniform flow if the moving elements do not change with the coordinate position (flow) during the flow process.

Secondly, laminar flow refers to the flow of fluid micro-clusters without mixing with each other, and the trajectory is purely imitative and methodical. For example, when water flows in a glass tube, inject a small amount of colored liquid, and you can see the laminar flow state in the tube. When the flow rate is low, the colored liquid forms a thin straight filament, and the water and the colored liquid are not mixed with each other, and the flow of the large punch is laminar flow.

Turbulence refers to the fluid movement in which flow elements such as velocity and pressure change randomly with time and space, and the trajectory of the particle points is tortuous and chaotic.

Finally, uniform flow can be divided into laminar flow and turbulent flow.

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In a non-pressurized flow or open channel flow, a non-constant uniform flow is not possible because the hydraulic element of the flow in the open channel is a function of time t and flow s. f(s,t).That is, the flow rate of the water flow in the non-constant flow of the nullah, and the depth of the water pin must change with time.

In general, the open channel flow often appears in the form of non-uniform flow, and only in special cases will uniform flow occur, and the conditions for the formation of uniform flow are:

1.long, straight prismatic channels;

2.The bottom slope is >0 and remains the same along the way;

3.The roughness of the channel did not change along the way;

4.The flow of water in the canal is constant and remains constant along the way.

The uniform flow line of the open channel is a parallel straight line, and the shape, water depth, and average flow velocity of the section do not change along the way, so the total head line, the water surface line and the bottom line of the canal are parallel, that is to say, the hydraulic slope J of the uniform flow of the open channel Douxiang, the slope of the piezometer pipe JP and the bottom slope of the channel I are equal to each other.

Because the unsteady flow of the open channel must be accompanied by the generation of waves, the streamlines cannot be parallel straight lines.

Is it true that someone said, "A uniform flow must be a constant flow"? Why? Solution:

This statement is false, a uniform flow is not necessarily a constant flow. Because a uniform flow is relative to space, i.e., the moving elements do not change along the flow, while a constant flow is relative to time, i.e., the moving elements do not change with time. The criteria for judging are different.

Constant flow vs. uniform flow are two completely different concepts.

Constant flow refers to the flow of moving elements that do not change with time, without positioning acceleration, and is observed at any point in space occupied by the fluid, while uniform flow refers to the flow of moving elements that do not change with space, without migration acceleration, and the moving elements at all spatial points occupied by the fluid at the same time are the same. In summary, constant flow does not change with time, while uniform current is the opposite.

Uniform flow of suspicion Sakura is ().

a.The local acceleration is zero.

b.Migration acceleration is zero.

c.The centripetal plexus acceleration is zero.

d.The combined acceleration is zero.

Correct Answer: The migration acceleration is zero.

Do you want to ask the question "how to distinguish between uniform flow and non-uniform flow"? To distinguish between the two, you can check whether the velocity or flow rate of the fluid remains constant in space or time, as follows:

1. Uniform flow: The velocity or flow rate of the fluid remains constant in space and time, which means that the fluid passes through the pipe, channel or surface evenly with the same velocity or flow, if you measure the velocity or flow rate of the fluid and find that they remain constant throughout the flow area, then it can be confirmed as a uniform flow, in this case, the velocity or flow rate is not zero.

2. Inhomogeneous flow: In inhomogeneous flow, the velocity band of the fluid or the flow rate is not constant in space or time, which means that the fluid passes through the pipe, channel or surface at different speeds or flows, if you measure the velocity or flow of the fluid and find that they vary in different positions or at different points in time, then it can be confirmed as a non-uniform flow, in this case, the velocity or flow rate is not zero, and there is a difference in space or time.

A constant flow is not necessarily a uniform flow. A constant flow can be either a uniform flow or a non-uniform flow. Uniform flow can be either constant flow or non-constant flow (non-constant uniform flow only exists in pressurized flow, non-constant uniform flow in open channel does not exist).

A constant flow is a flow in which the elements of motion do not change with time, without localized acceleration, and are observed at any point in space occupied by the fluid, at which the fluid velocity (including magnitude and direction) does not change with time, that is, the velocity is constant. But the velocity at different points in space of a constant flow can be different, and of course it can be the same.

The basic equation for uniform flow is described as follows:

The basic equation of uniform flow is an equilibrium relationship obtained according to the phase equilibrium of external forces acting on a constant uniform flow section. The formula applies to both laminar and turbulent flows.

The relationship between head loss and shear stress along the uniform flow of a circular pipe can be expressed by the formula illustrated: this formula is called the basic equation of uniform flow. It shows that the head loss hf along the total flow of any cross-section shape is directly proportional to the flow length l and the average shear bypass stress 0 of the wall, and inversely proportional to the hydraulic radius r.

Main concepts: mass force, surface force, viscosity, viscous force, compressibility coefficient, thermal expansion coefficient. Note: The mass force in the vast majority of flow problems is gravity only. Its unit mass force f is customarily selected as f=(0,0,-g) in Cartesian coordinate system

Viscous is the physical property of the fluid itself, while viscous force is the manifestation of this property of the fluid when it produces shear flow. Newton's shear formula: t=ua*du dt

Difficulty analysis: To describe fluid flow from Euler's point of view, the surface force analysis of the fluid in the control body should include the force on all possible surfaces. These wax beam surfaces may be free surfaces or contact surfaces with surrounding fluids or face walls.

The relationship between stress and deformation rate reflected in Newton's shear formula is only true when Newtonian fluids are in so-called pure shear motion, and in general for general flows, Newton's formula.