What is hydrodynamic pressure effect and what does dynamic and static pressure mean in hydrodynamics

When the moving ring rotates, because there are many micropores on the surface of the static ring, the rotation of the moving ring makes its surface and the micropores on the surface of the static ring form an averging gap fluid film layer, so that each hole is like a micro-dynamic sliding bearing.

That is, when another surface slides on a porous end face, hydrodynamic pressure is created above and around the hole.

force, which is the hydrodynamic pressure effect.

Hydrodynamic lubrication = lubrication + fluid lubrication + hydrodynamic lubrication.

1. Lubrication: there must be lubricant and lubricating oil or fluid grease to lubricate between the two friction pairs;

2. Fluid lubrication: lubrication is divided into boundary lubrication and fluid lubrication, and the two friction pairs are not completely separated by lubricants, and those with high-point contact are called boundary lubrication; The formation of a complete oil film between the friction pairs is fluid lubrication, which is a very ideal lubrication state;

3. Hydrodynamic lubrication: the formation of fluid lubrication is either small enough load and large enough viscosity to form a thick oil film, or the two friction pairs are stretched apart to form a thick oil film by pressure. This pressure is divided into static pressure and dynamic pressure, hydrostatic lubrication is to rely on external force, such as a high-pressure pump to press grease into it to make it have enough oil film thickness, generally used in the equipment start-up stage; Hydrodynamic lubrication is to rely on the movement between the two friction pairs to squeeze the lubrication from a larger space to a smaller space, and at the same time, due to the existence of friction in the fluid, a large pressure (dynamic pressure) is generated, and an oil film of sufficient thickness is formed to support the two friction pairs.

Dynamic pressure. When the object is moving in the fluid, on the surface facing the direction of the fluid movement, the fluid is completely blocked, the fluid velocity here is 0, its kinetic energy is converted into pressure energy, the pressure increases, and its pressure is called the total obstructed pressure (referred to as total pressure or total pressure, represented by p), and the difference between it and the pressure at the undisturbed place (i.e., static pressure, represented by p static) is called dynamic pressure (represented by p motion).

Static pressure refers to the linear motion of an object at rest or at a uniform velocity.

The pressure on the surface. Its unit is: PA. Static pressure plus dynamic pressure equals full pressure.

What does dynamic pressure and hydrostatic pressure mean in fluid dynamics?

Dynamic pressure in fluid dynamics refers to an internal pressure exerted on an object by air or other media when the fluid is moving, while static pressure refers to an internal pressure acting on the surface of an object when the fluid is at rest.

Summary. In fluid dynamics, the kinetic energy and static pressure of a fluid are closely related. According to Bernoulli's theorem, kinetic energy and static pressure are interrelated when the fluid is in a pipe or through a shrinking device.

An increase in kinetic energy is usually accompanied by a decrease in static pressure and vice versa. When a fluid flows from one region to another, the change in kinetic energy and static pressure leads to a change in flow velocity and pressure. Specifically, when the flow velocity increases, the collisions between the molecules of the fluid also become more frequent and intense due to the increase in the kinetic energy of the fluid, resulting in a decrease in static pressure.

Conversely, when the flow velocity decreases, the collisions between the molecules become fewer and weaker due to the decrease in kinetic energy, resulting in an increase in static pressure.

I'm still a little confused, can you be more detailed?

In fluid dynamics, the kinetic energy and static pressure of a fluid are closely related. According to Bernoulli's theorem, kinetic energy and static pressure are interrelated when the fluid is in a pipe or through a shrinking device. An increase in kinetic energy is usually accompanied by a decrease in static pressure and vice versa.

As the fluid flows from one region to another, the change in kinetic energy and static pressure leads to a change in flow velocity and pressure. Specifically, when the flow velocity increases, the collisions between the fluid molecules also become more frequent and intense due to the increase in the kinetic energy of the fluid, resulting in a decrease in the static pressure. Conversely, when the flow velocity decreases, the collisions between the molecules become less and less sluggish due to the decrease in kinetic energy, resulting in an increase in static pressure.

The change of the state of motion, unlike the solid, it is possible to convert the force into deformation, the pressure phenomenon of the fluid and the strong coupling of the motion phenomenon, it is difficult to say who is the cause and who is the effect of the force and the motion, this is a chicken-and-egg problem) and for non-viscous fluids, the sum of static pressure and dynamic pressure is a constant by Bernoulli's equation. It gives the impression that the dynamic pressure can be "converted" to static pressure by reverse pressure gradient deceleration. But don't think that the dynamic pressure energy acts directly on the object!

As long as you understand the essence of dynamic pressure, the doubts will be very clear. Along the axial direction, it is okay to have a uniform pressure, because the pressure here is static. The change in velocity along the axial direction is not due to a pressure gradient, but rather to a viscous force.

Dynamic pressure is not "transformed" into static pressure here, so there is no point in discussing dynamic pressure. <>

The problem of dynamic pressure has also been bothering me, any flow through the solid surface of the initial stage of the flow must be uneven, the speed will change, for the stable flow fluid will eventually reach a stable state, the process of force change is not understood, the resistance is gradually larger or gradually smaller, or always the same, simple analysis, the fluid flow process encounters obstacles, obviously the dynamic pressure will be converted into static pressure, the static pressure will increase to a certain extent will break through the obstacle bypass, the reason may be the static pressure of the isotropy, The dynamic pressure also flows to the low pressure area with the static pressure, and does the turning consumption of the dynamic pressure consume no fluid energy? Obviously, the boundary layer theory does not seem to address this issue, it seems that if it is an elastomer or a plastic? And how is the object resistance determined during the flow process?

Assuming that the wind wheel is placed in a constant wind field, how does the resistance of the wind wheel change? How does it work? It can be determined that the speed of the wind wheel is getting faster and faster, the angle of attack is getting smaller and smaller, and the lift force is getting smaller and smaller, and finally the maximum speed is reached when the drag moment lifting moment balances the angle of attack, but what about the change in resistance.

The formula for calculating hydrodynamic pressure is 1 2* *v 2, that is, dynamic pressure is generated only if the fluid has velocity. In deriving the dynamic pressure distribution of the relative motion of non-parallel plates, we use the assumption that there is no gradient of pressure in the vertical direction.

So the question arises, for the fluid, the boundary velocity of the fluid in contact with the fixed version is zero, then the dynamic pressure is zero, so that the pressure will have a gradient in the vertical direction, is this contradictory to the hypothesis? When it comes to hydrodynamic lubrication bearings, is it true that stationary bearings are not subject to hydrodynamic pressure? When we fan the air with a fan, the pressure on the side of the fan facing the air will rise, because the air has inertia, and it must be pushed forcefully to move, and this force is given by the fan.

If, according to you, fluids flow very easily, then how can the pressure increase on the windward side of the fan? Dynamic pressure is not a real pressure (only static pressure is) and does not directly produce interaction forces. It represents the work required to reduce the velocity of a fluid element to zero in motion.

The reason why the word "pressure" is added to the name of dynamic pressure is completely a clever idea of early fluid mechanics researchers in combination with Bernoulli's phenomenon. Bernoulli's phenomenon can be described as follows: if a fluid element is decelerated along the direction of the flow, and there is no viscous force or physical force (such as gravity) acting on it, it can only enter the high pressure region from the low pressure area. Many people understand the Bernoulli phenomenon and like to use deceleration to cause pressure to rise, which is actually the reverse of cause and effect, originally the countercurrent pressure gradient caused the fluid to decelerate, and the result is that the fluid motion is coupled by force to give people the illusion that the fluid deceleration causes the pressure to increase.

In fact, since the fluid does not have the ability to resist deformation, its forces are quickly converted to. <>