I want to make continuous viscosity monitoring of a ceramic slurry by measuring the drag of a slender body immersed in it.
The body is slender, axisymmetric in shape, and immersed in a ceramic slurry stream so to have a Reynolds number (based on its maximum diameter and slurry speed) of about 100. The slender body aspect ratio (length/maximum diameter) should not exceed 3.
What is the best body shape to maximize viscous drag ?
Dear Mr. Boulahia,
I asked a very precise question and you keep me sending an Elementary fluid mechanics book for undergraduate students. Where in this book I can find the answer to my question ? I have tons of this kind of books.
Probably, this is a way to increase your RG score since you have only 20 research items and only 24 citations, even if you have the RG slightly higher than mine..
Do not loose your time with non-useful answers and try to work scientifically harder.
Sorry, but I cannot thank you. Hope I do not receive more similar answers.
I would think about a drop-shaped body (round tip and narrow tail). Such a body should be tolerant about small variations of flow angle and it avoids regions of flow separation where the two phases could separate. But I am interested in other opinions.
How do you intend to immerse the body into the flow and how do you measure the drag force?
Dear Mr. Riess,
thanks for your answer which coincides with what I am doing.
Any idea on the body particular shape ?
The body is attached to a slender elliptic bar and I measure the torque at the free end.
Regards
Sorry, I cannot give you an air foil shape code. I suppose, the tip depends on the stability of the flow (variation of flow angle) that you expect. And the 3:1 aspect ratio more or less defines the shape. In the end, it does not have to be the perfectly streamlined body.
Dear Mr. Carlomagno
From your answer to Mr. Riess I understand that you already have an experimental setup for the measurement of torques on the slender body.
I just wonder whether the direct measurement of forces using very precise and cheap dynamometers could be used. A slender body denser than the slurry would be kept hanging from the rig and immersed in the slurry in an open channel flow. The drag force is calculated via an overall force balance on the body.
As for the body shape, higher aspect ratios should increase the viscous drag. Also, too much fontal area (blunt body) will promote early (positional) boundary layer detachment, decreasing the viscous drag.
As you can see from the attached file, calculations on two different shapes at two different Reynolds numbers show that, in this regime, frictional drag is much influenced by the body shape but the total one (which is what I measure) is practically not.
Regards
Nice figures !
With your original question in mind, I believe the frontal area of object 1 and 2 should be the same for a better comparison. From the figures, it seems, the frontal area of object 2 is greater. The transversal displacement of streamlines (which are mainly related to form drag) is highly dependent on the frontal area.
Since maximum viscous drag is desired, I wonder what would happen with the objects rotated by 180º, at the same Reynolds values.
Regards
Dear Mr. Peçanha,
we are working with dimensionless parameters, so the larger appearing dimensions of object 2 is only matter of representation. You can scale figures at your pleasure.
Attached you will find the object rotated of 180o and relative results.
Regards
Thanks for clearing the frontal area differences of objects 1 and 2.
Too much trouble (eddies) in the wake of object 3 (object 2 rotated by 180º), clearly associated with boundary layer detachment. Consequently, a lot boundary layer coverage lost in the rear surface, that is, viscous drag lost. No good.
Since transversal displacement and bending of streamlines are determinant of form drag, may be a thin flat plate (parallel faces) could work as desired, increasing the contribution of viscous drag.
I am measuring the total drag and fortunately also the form drag is a function of Re.
A flat plate has the problem that its drag depends on its angle of attack and may, in case, vibrate.
Regards
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