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Old 08-05-2020, 03:50 PM   #131 (permalink)
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Putting plasma actuators all over a car would be akin to putting golf ball dimples all over one. Friction drag is not the goal.

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4 Flow control applications
4.1 Vortex generator
4.2 Active noise control
4.3 Supersonic and Hypersonic flow control
4.4 Flight control
en.wikipedia.org/wiki/Plasma_actuator
Quote:
Modeling
Various numerical models have been proposed to simulate plasma actuations in flow control. They are listed below according to the computational cost, from the most expensive to the cheapest.
  • Monte carlo method plus particle-in-cell;
  • Electricity modeling coupled with Navier-Stokes equations[19];
  • Lumped element model coupled with Navier-Stokes equations[20]
  • Surrogate model to simulate plasma actuation.[21][12][22]
The most important potential of plasma actuators is its ability to bridge fluids and electricity. A modern closed-loop control system and the following information theoretical methods can be applied to the relatively classical aerodynamic sciences.
Interestingly, Monte Carlo processing may improve CFD analysis:
https://sciencedaily.com/releases/2020/06/200629124108.htm
Quote:
Analysis of complex geometric models made simple
Monte Carlo method dispenses with troublesome meshes
Date:
June 29, 2020
Source:
Carnegie Mellon University
Summary:
Researchers have developed an efficient new way to quickly analyze complex geometric models by borrowing a computational approach that has made photorealistic animated films possible.
.....
Crane and Sawhney's work revives a little-used "walk on spheres" algorithm* that makes it possible to simulate a particle's long, random walk through a space without determining each twist and turn. Instead, they calculate the size of the largest empty space around the particle -- in the lung, for instance, that would be the width of a bronchial tube -- and make that the diameter of each sphere. The program can then just jump from one random point on each sphere to the next to simulate the random walk.

While it might take a day just to build a mesh of a geometric space, the CMU approach allows users to get a rough preview of the solution in just a few seconds. This preview can then be refined by taking more and more random walks.
*Comports with Bucky Fuller's Synergetic Geometry.

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Old 08-05-2020, 04:29 PM   #132 (permalink)
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dimples all over

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Originally Posted by freebeard View Post
Putting plasma actuators all over a car would be akin to putting golf ball dimples all over one. Friction drag is not the goal.


en.wikipedia.org/wiki/Plasma_actuator


Interestingly, Monte Carlo processing may improve CFD analysis:
https://sciencedaily.com/releases/2020/06/200629124108.htm

*Comports with Bucky Fuller's Synergetic Geometry.
Above 20-mph, all automobiles are already covered in dimples, by virtue of supercritical Reynolds number.
If you introduce plasma in between the body surface and boundary layer, the air will separate from the plasma. No benefit.
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Old 08-05-2020, 05:08 PM   #133 (permalink)
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...the air will separate from the plasma...
The [ionized] air is the plasma. It doesn't separate, it accelerates. Locally, under control.

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Either a direct current (DC) or an alternating current (AC) power supply or a microwave microdischarge can be used for different configurations of plasma actuators.... The performance of plasma actuators is determined by dielectric materials and power inputs, later is limited by the qualities of MOSFET or IGBT.
[snip]
Manipulation of the encapsulated electrode and distributing the encapsulated electrode throughout the dielectric layer has been shown to alter the performance of the dielectric barrier discharge (DBD) plasma actuator. Locating the initial encapsulated electrode closer to the dielectric surface results in induced velocities higher than the baseline case for a given voltage. In addition, Actuators with a shallow initial electrode are able to more efficiently impart momentum and mechanical power into the flow.[4]

No matter how much funding has been invested and the number of various private claims of a high induced speed, the maximum, average speed induced by plasma actuators on an atmospheric pressure [conviction[?], without any assistant of mechanical amplifier (chamber, cavity etc.), is still less than 10 m/s.[5]

Influence of temperature
The surface temperature plays an important role in limiting the usefulness of a dielectric barrier discharge plasma actuator. The thrust produced by an actuator in quiescent air increases with a power law of the applied voltage. For voltages greater than a threshold, the exponent of the power-law reduces limiting the thrust increase, and the actuator is said to have “saturated,” limiting the actuator’s performance.
en.wikipedia.org/wiki/Plasma_actuator
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Old 08-07-2020, 12:56 PM   #134 (permalink)
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accelerates

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Originally Posted by freebeard View Post
The [ionized] air is the plasma. It doesn't separate, it accelerates. Locally, under control.


en.wikipedia.org/wiki/Plasma_actuator
1) The air adjacent to the body needs to be at rest. Zero movement.
2) If it CAN move, it will move in the direction of low pressure.
3) If it's in the aft-body, all the air will move to just ahead of the windshield header.
4) As it does this, the counter-flow will trigger separation, eddies, followed by full-blown turbulence.
5) This separated flow is exactly what is to be avoided.
6) You'd end up with the highest imaginable drag.
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Old 08-07-2020, 02:06 PM   #135 (permalink)
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1) The air adjacent to the body needs to be at rest. Zero movement.
Why? Think of it like a rolling floor in a wind tunnel. It virtualizes an air cushion near to the body.
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6) You'd end up with the highest imaginable drag.
...if you put them in all the wrong places.
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Old 08-12-2020, 12:40 PM   #136 (permalink)
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near the body

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Why? Think of it like a rolling floor in a wind tunnel. It virtualizes an air cushion near to the body.

...if you put them in all the wrong places.
The last thing in the world that you want is for the air, immediately adjacent to the body of the car to 'move.'
The ability of this air to stay 'pinned' to the surface is the only thing that separates you from a car with Cd 0.88.
If you cover a car with plasma, you're going to get Cd 0.88. It's impossible for it not be happen. It goes directly to the operational foundation of fluid mechanics, especially boundary layer dynamics.
All a moving-floor wind tunnel facilitates is, lack of boundary layer under the car ( which never made a difference with passenger cars anyway), and the ability to study airflow around the rotating wheels, of which, the merits have yet to be properly, and scientifically addressed in the popular literature.
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Old 08-12-2020, 06:37 PM   #137 (permalink)
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Bad analogy?

I have not idea, but the electrified air may still effectively adhere.
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Old 08-19-2020, 12:02 PM   #138 (permalink)
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adhere

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Bad analogy?

I have not idea, but the electrified air may still effectively adhere.
What they're not addressing, is the fact that, base pressure is ruled by the pressure at the separation line.
The wake remains the full frontal area of the rig, and its wake pressure the same. They've done nothing to alter that fact.
Altering the shape of the wake does nothing to address the pressure, and could actually exacerbate drag by introducing velocities and vorticity which otherwise would not exist. It can be worse than the turbulence they're trying to abate.
What we're targeting is, a controlled deceleration of the air, while rebuilding static pressure, the domain of a streamlined body.
Until they present a more complete argument, their claims remain quite dubious and half-baked.
A simple, sexy, falsehood may sell better than a tedious, complicated truth, but at the end of the day, physics and reality may spoil the party.
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Old 08-19-2020, 02:13 PM   #139 (permalink)
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base pressure is ruled by the pressure at the separation line.
Vas ist das?

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What we're targeting is, a controlled deceleration of the air, while rebuilding static pressure, the domain of a streamlined body.
Until they present a more complete argument, their claims remain quite dubious and half-baked.
I don't pretend to understand, but I'm hopeful. But then I'm still hopeful about the Scuderi Cycle engine.
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Old 08-19-2020, 04:02 PM   #140 (permalink)
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Vas ist das?

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Originally Posted by freebeard View Post
Vas ist das?


I don't pretend to understand, but I'm hopeful. But then I'm still hopeful about the Scuderi Cycle engine.
1) where the attached flow separates from the body is, by definition, the separation line. The back of a truck box, or trailer van in this case.
2) turbulent boundary layer flow will easily remain laminar if it's flowing towards a low pressure ( just ahead of the windshield header/ roof apex ).
3) beyond this location of lowest pressure, the turbulent boundary layer is in jeopardy of separation if it encounters pressure which is increasing any faster than it would over a 'streamlined' body ( template).
4) the pressure is governed by how rapidly the body cross-section reduces, which causes a pressure rise as it gives up its position of displacement, attempting to get back where it was before we came along. Loitering in place.( Bernoulli Theorem ).
5) all a streamline body does is, give the air twice as much distance to slow back down, as was used to accelerate it from rest. You can actually measure this with string. It's a fast pelagic fish profile ( bluefin tuna viewed from the top ) with 1/3rd of the body accelerating the air from rest, and the remaining 2/3rds as a deceleration ramp, long enough to let the air recover its former, pre-vehicle position. It's the perfect ratio of accel/ decel. Anything more aggressive and the pressure rise exceeds what the boundary layer can tolerate.
6) all the air in the back of the car wants to go to the windshield. Outer flow, above the boundary layer strafes the boundary layer, shooting kinetic energy at it by way of glancing blows. If the surface of the car falls away to rapidly, the bullets of air just ricochet off the top of the boundary layer like a flat stone on a pond, making it impossible to hold the layer in place.
7) once this angle grows beyond streamlined, the layer begins to flow forwards to the windshield, rolling up into eddies, then lifting off the car ( separation ), in full-blown turbulence.
8) turbulence is pure entropy. It's an irreversible loss of kinetic energy. It can never be recovered by any means, and literally heats the air around it until warn down by viscous forces, hundreds of feet behind the car. The plasma-actuators do nothing to address this issue.
9) without streamlining, all we have is a wake of turbulence. Useless! Costly. Low performance.

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Last edited by aerohead; 08-19-2020 at 04:07 PM.. Reason: add tidbits
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