我是黄韬博，我2010 年高考以优异的成绩考上全国重点大学北京林业大学，经过刻苦钻研，我在导师韩莹莹的指导下，我于2014 年获得了宝贵的毕业论文《野生达乌尔黄鼠在繁殖期与非繁殖期卵巢上皮神经生长因子及其受体的免疫定位》。我身高1 米88。我是韩老师的优秀学生，而你们这些侏儒不但学习差，还长得矮，你们不觉得你们还有脸活在世上很夸张吗？我真是觉得遇到你们很倒霉。你们都是愚蠢的畜生，我的邮箱是[email protected]

Howdy Bilal Ahmad, Excellent! "How."

I logged in to your ResearchGate site and I am confident you comprehend how difficult your question turns out to be. I offer a view of the relevant physical dynamics of the process you wish to comprehend from my viewpoint. It may ring true for you.

We start before the separator is in use visualizing a generic cyclone separator for removing dust from air. It is Stairmand style with tangential input to a cylindrical section above a conical section. The lower end of the cone is open for dust removal with flow assistance. The main outlet is concentric to the cylinder section and projects into the cylinder volume to reduce direct input – output flow.

The separator function begins with startup of the mill exhaust blower. Input flow increases the pressure in the separator and induces exhaust flow from the separator via the main outlet, the vortex finder, and via the dust removal opening. The inflow proceeds to the surface of the cylinder which it is forced to follow while the outflow proceeds without strong character due to the pressure gradient.

Shear between the input flow and the quiescent air in the separator volume drags it into rotation and for an initial period this process extends down the surface of the separator and downward in its interior. Dust in the inflow is denser than air and has higher inertia so it moves through the air stream toward the separator inner surface. To this point there is no flow reversal because only the air that had been in the separator volume before startup is leaving. However, rotation in the volume of the separator is increasing because of shear stress from the input flow. Eventually the outflow will begin to rotate.

The two rotating structures in a vortex separator are very different. Per Isaac Newton’s 2nd law, fluid motion does not change speed or direction (velocity vector) without a force. The relevant forces present in a cyclone separator are a pressure gradient force directed away from the high-pressure flow stagnation on its inner surface and the force directed toward the low-pressure outlet at the vortex finder. Measurements have shown that the outer vortex approximates a “free vortex” with radially decreasing tangential velocity. It is forced by bulk flow through the separator. The tangential velocities in the outer vortex are a balance between momentum of the input flow and drag at the surface of the separator. A secondary flow from the stagnation point is a radial return flow along the top of the separator. The main flow is downward into a spiral helix along the inner wall of the separator. The uniform bulk flow from the supply piping is rapidly converted to the radially decreasing flow found in the established outer vortex. Measurements also have shown that the inner vortex is a “forced vortex” with a radially increasing tangential velocity. Its rotation is due to convergence of bulk flow vorticity to the vortex finder to form a vortex rotating like a solid.

A tornado exhibits a different process from that of either the inner or the outer vortex in a separator. A tornado rotates because the atmosphere in which it forms due to convection has been rotating with the earth and convergence of that angular momentum (vorticity) in the tornado causes increased tangential velocities. Convergence of the bulk rotation in the separator volume yields high tangential velocities in the inner vortex, but the angular momentum source is the deflected, rotating flow of the outer vortex not the rotation of the earth.

The volumetric source of the inner vortex is the outer vortex. Measurements have shown that radial flow between the outer and inner vortices occurs over the full height of the vortices in the separator. It starts when the separator volume becomes pressurized by system startup and adapts as the balance between inertia and pressure gradient force changes while the flow evolves towards a quasi-steady state. Therefore, the flow reversal volume starts in the input/output volume near the top of the separator and extends downward as the vortices develop. It exhibits a so-called “vortex end” at its lower extremity. The vector of angular momentum does not change direction although the axial motion does reverse. The reversal of the flow occurs around the whole circumference so there is no precession response involved. This flow from the outer vortex to the inner vortex requires either a conical shape or a flat vortex limiter plate in the lower portion of a separator to maintain tangential velocity and separation efficiency in the outer vortex as the volume of the flow decreases there.

A “vortex tube” is a volume of fluid rotating about an axis. The inner vortex is a “vortex tube.” The strength of a “vortex tube” is measured by circulation of the fluid, where circulation is the line integral of velocity along a closed path around the vortex tube. A theorem of Helmholtz states that the strength of a “vortex tube” is constant along its length, which theorem implies that a vortex cannot end internally in the fluid, but it must be attached to a surface or itself at both ends. The downstream end of the inner vortex is attached in or beyond the vortex finder. However, while the outer vortex is not a “vortex tube,” it is a rotating mass forced by pressure, momentum, drag, and deflection. Since all circulation within the inner vortex is driven by the rotation of the outer vortex as the flow converges toward the vortex finder outlet, the developed rotation of the outer vortex at its “vortex end” supplies the circulation of the inner vortex at its “vortex end” and a smooth flow reversal with constant circulation like a vortex tube may exist. When separated from the outer vortex the upstream end of the inner vortex attaches to the separator wall or vortex limiter plate as shown by Peng, et. al.

It is important to recognize that while the rotation of the output vortex is due to the forced rotation of the input flow that forms a “free vortex,” the intensity of the vortex rotations is controlled by the process fan driving the flow. Further, while the matching of the outer and inner vortices that enable a “stable” vortex end with flow reversal contained therein is successful under limited conditions, attachment of a vortex tube to a solid surface is much stronger and will occur whenever possible. Therefore, a vortex limiter designed to be an optimum “vortex attachment surface” has great potential benefit. At flow rates less than a critical value, the vortex closure through vortex matching would be present in the return flow volume at the vortex end, but above the critical flow value a “vortex attachment surface” would center the inner vortex and reduce surface dust disruption by a rotating “vortex tube” attached to the vortex wall as observed by Peng, et. al. Flow to the inner vortex does not enter through its vortex end in any case, so the attached vortex would behave as an inner vortex matched to the outer vortex in all essential respects. Such an attachment also may alter the complex inner vortex motions of precession and nutation observed in experiments.

It would be interesting to see results from an experiment in which the axial location of the “vortex attachment surface” were adjusted automatically by sensing the low pressure of the vortex core when it is attached and lowering the surface to release it to restore a free vortex end. The location of the vortex end as a function of input flow and particle loading would be simple to record. It would not be practical in a commercial design, but the data would be very valuable in clarification of the dynamics of a separator. It would be a relatively simple modification to several of the current separator designs used in experiments. A simple retrofit, mounting a “vortex attachment surface” at the vortex length identified by the dust ring on existing separator surfaces, should be feasible in many cases.

Well, I hate waiting, and this view may be an opening for thoughts of your own for now. After all, somewhere in his Essays Montaigne has noted that published thoughts belong to the author, but after you have read them, they and what you conceive are your own. Happy Trails, Len

P.S. Discussion, exploration, is delightful, do not hesitate to explore this phenomenon. "Truth" is rarely true.

Howdy Bilal Ahmad, you are not receiving many answers to your question. I have been working on my answer because this question is an excellent opportunity to understand my own work more deeply. I had prepared a revision before I got mired in the literature of "coherent structures" and offer a portion of it here as a much better wording of a better understanding than my first answer. A longer version of this including articles read is now on my ResearchGate project "Whence Insight." I shall improve that with better treatment of structure coherence as time goes by.

An answer, heuristic and descriptive rather than mathematically rigorous, but an answer:

Reverse Flow Startup

Our thought experiment starts before the separator is in use, visualizing a generic cyclone separator for removing dust from air. It has a tangential input to a cylindrical section above a conical section. The lower end of the cone is open for dust removal. The main outlet is concentric to the cylinder section and projects into the cylinder volume.

The separator function begins with exhaust from a process. Input flow increases the pressure in the separator and forces flow from the separator via the main outlet, the vortex finder, and via the dust removal opening if it is not sealed. The inflow proceeds to the surface of the cylinder which it is forced to follow in a downward helix while the outflow proceeds without strong character due to a pressure gradient force. Shear between the input flow and the air in the separator volume drags that air into rotation and for an initial period this process extends down the surface of the separator and downward in its interior (Peng, et. al, 2005). Dust in the inflow helix is denser than air and its greater inertia forces it through the air stream toward the separator inner surface.

The source of the air flowing through the inner vortex is the inflow helix. Measurements have shown that radial flow between the outer helix and inner vortex occurs over their full height in the separator (Fig. 10, Peng, et. al., 2002). It starts when the separator volume becomes pressurized at system startup and adapts as the balance between inertia and pressure gradient force changes while the flow evolves towards a quasi-steady state. Therefore, the flow reversal process starts near the top of the separator and extends downward as the internal circulation develops. The vector of angular momentum does not change direction between the outer helix and the inner vortex, although the axial motion does reverse. The reversal of the flow occurs around the whole circumference. The tangential flow responds to either a conical shape or a flat vortex limiter plate in the lower portion of a separator to maintain separation efficiency in the outer vortex as the volume of the helix flow decreases there.

Pisarev, et. al., (2012) found that “In the 85 cm long swirl tube the vortex core always initially was seen to bend to the wall, at least for all flowrates high enough to form a vortex at all (higher than 20 m3/h).” What does happen to form a “flow reversal volume” during startup? The outflow vortex is bounded by the vortex finder and flow dynamics that require most of the flow to exit there. The initial form of the outlet vortex is affected by convergence of bulk rotation vorticity in the separator and would resemble a funnel cloud that extends toward the ground due to a strong cumulus cloud updraft. Whether the helix and vortex connect in a “flow reversal volume” or the inner vortex attaches to a surface will be dependent on an individual case in a specific separator. Since the function of the separator in operation will depend on a quasi-steady state, this transient process will not be critical unless the inner vortex remains attached to the inner surface of the separator, like a tornado after touchdown, and disrupts orderly movement of the separated dust to the dust outlet.

Well, there is more in the full version if you are interested,

Happy Trails, Len