best aerodynamic solution

[lorenzoneri]

Hello everyone
I am new to the forum,
in the past I have tried several times to learn the use of some cfd program, but with little results.

I would have a question to which probably experts like you will be able to answer without even opening the cfd program.

I am a model of remote boats,
in particular those called hydro,
as you can see in the attached photos are set up by a central body and two side boots.
in planata the points of support are only the extremities of the boots and the stern husk, which sink only a few millimeters.
my question is, what is the best aerodynamic configuration of the boots?
there are two schools of thought, that of the photo to (white hull)
and that of the photo b with the "tail" up (wooden hull).
considered traveling at 80km/h on a firm surface (water)
what interests is the least possible resistance to progress.

thanks in advance,
Lorenzo

 

[thor105]

as an aerospace engineer i can assure you that there is no better solution regardless, because a solution that provides less resistance to advancement, but keeping it stable on the acuqua probably makes it unmanageable at the same time, while one that instead makes sure that the boat is very maneuverable is likely to make it too sensitive to shales or disturbances in general. you have to see the field where you have to cite the boat and then make a special hull. and is one of the reasons why, despite the many cfd simulations, formula 1 machines have all different performance.

 

[lorenzoneri]

First of all, thanks to the quick response to a newcomer like me.
I think we have to deal with one thing at a time,
trying to understand why it works is my greatest passion,
even more than realizing it and seeing it run.
I think we have to deal with one thing at a time,
if the instruments of the cfd allow me to decrease the resistance with the air,
This is one thing you can calculate,
dynamic negative effects of stability are a risk that should be considered,
I usually tell you that the arrangement and stability of boats like this are given
from the distribution of weights, from the appendices that touch the water and from the thrust of engine rudder and fin.

at this moment I would like to know which solution aerodynamically is better, if the best solution will bring me other bets, you can recover by changing other things in the boat.

I agree there is no better solution at all,
I ask you only what is the solution that offers less resistance to progress.

Thank you.
This is a topic that I really like,
Lorenzo

 

[Fulvio Romano]

I am not an expert, but I would say that the elements that reduce aerodynamic performance are basically three:
- section cross, that is the maximum section (orthogonal to advancement). the smaller the resistance
- Right in front of me, "open the air." the more it is to tip, the more it reduces the pressure of stagnation of the air that stops in front
- behind that "closes the air." the more it is to tip, the more you reduce the vortices that suck the boat from behind. Here it also takes clean, unrounded surfaces, to detach fluid fillets.

Actually the three-point trimarans (which are not the ones you say, but they look like us) that I have seen, usually they are quite different, like the sarnic archdiocese. have a flat monocane behind, with at least two orders of skates, and two boots ahead with skates and step. All these elements reduce friction with water in the various contacts between this and the hull.

p.s.
But shouldn't "hydro" fly too?

 

[thor105]

First of all, thanks to the quick response to a newcomer like me.
I think we have to deal with one thing at a time,
trying to understand why it works is my greatest passion,
even more than realizing it and seeing it run.
I think we have to deal with one thing at a time,
if the instruments of the cfd allow me to decrease the resistance with the air,
This is one thing you can calculate,
dynamic negative effects of stability are a risk that should be considered,
I usually tell you that the arrangement and stability of boats like this are given
from the distribution of weights, from the appendices that touch the water and from the thrust of engine rudder and fin.

at this moment I would like to know which solution aerodynamically is better, if the best solution will bring me other bets, you can recover by changing other things in the boat.

I agree there is no better solution at all,
I ask you only what is the solution that offers less resistance to progress.

Thank you.
This is a topic that I really like,
Lorenzo

forget that on the boat also acts the force of portance (or deportance in this case) that causes the boat to have a proper penetration of the hull in water. and there is also another basic "mistake", that is to consider water as a still fluid compared to the boat. apart from the fact that typically in cfd simulations (as in those of wind tunnel) the object and fluid in motion is considered firm, there is also to take into account that the body is not immersed in a single homogeneous fluid, but it is in contact with two different fluids (water and air) that are in contact with each other. This generates a wave system that substantially changes the fluid dynamic field. This may seem unconscious, but he had created not a few problems in the study of the fluid dynamics of the first Latin rascal, to which he had attended my professor of aerodynamics and a group of my former university colleagues who also advise for ferrari (to make you understand that they are not the first arrived). Unfortunately the aerodynamics hardly allows to give simple answers, especially when trying to get to soothe on the tenths of a second.
However I will try to give you as much as possible a guideline that can be followed always.
in the boats the aerodynamic resistance is given: shape resistance, ski resistance, induced resistance, added mass effect, resistance due to the ondous system.
since the added mass effect is not purely aerodynamic, but is a "secondary" effect and that the resistance of the ondous system is not easily determinable; I would say that any form of the different appendixes, allow to reduce the resistance, shape and the one of trail, can be considered a good choice.
but this is the classic answer that would also give monssieur de lapalisse.

 

[lorenzoneri]

I am deacon with what you have listed,
but I don't know how to consider the flow behind the boot,
as it must be considered that under the boot does not pass air and behind it there is a depression zone,
Perhaps the tail to the up has the task to occupy this area that is of depression and collect from the walls the air to bring it back behind the boot limiting the depression.

Lorenzo

 

[lorenzoneri]

I would say that any form of the different appendixes, allow to reduce the resistance, shape and the one of trail, can be considered a good choice.
but this is the classic answer that would also give monssieur de lapalisse.

I read on the internet the definitions of the aforementioned resistances,
to what I understood to reduce the resistance of form I have to point to the boot and not a rounded surface,
and for the ski resistance perhaps could be useful that tail up.

What do you say?

Lorenzo

 

[thor105]

I read on the internet the definitions of the aforementioned resistances,
to what I understood to reduce the resistance of form I have to point to the boot and not a rounded surface,
and for the ski resistance perhaps could be useful that tail up.

What do you say?

Lorenzo

for the ski resistance is not only important the edge of the profile, but also the edge of attack and the relationship between cross section and profile rope, this for a detachment speech of the boundary layer from the profile resulting in huge increase of the ski resistance.
talk about s.l. detachment for boats may seem out of place, given the speeds in play, but taking into account that it depends on the dynamic pressure and therefore on the speed, but also on the density of the fluid. Since water has a density of 10 times greater than air, this means that in order to have the same dynamic pressure conditions it is sufficient that the speed is 30% of that in the case of air.
I know I can generate more questions than answers, but unfortunately the matter is not simple at all.
Navier-stokes cross and delight of aerospace engineering students all over the world.

However, due to the greater density of water, I would try to reduce the resistance of the immersed part as much as possible, if I could reduce the reduction would undoubtedly be more consistent.

 

[Er Presidente]

fast, before the blow!
inside the water the resistance of skiing and that of form must find a balance that is different than in the air.
moral can happen that a "tronca" tail reduces the surface "bagnata" and is advantageous compared to a tapered tail, which would improve the trail, but probably not enough to compensate for the disadvantages of the increase of the wet surface.
in the air could happen the reverse and then the "beak" could serve to improve the trail in the air without "inflating" the braggings of the tail truncated in the water.

all "arm" and with the benefit "of inventory2.

Hi.

 

[lorenzoneri]

I deduce from your considerations that the situation is greatly messed up.

I deduce two possible solutions:
1. You teach me to use a cfd program and I do the simulations of the various configurations.
2. I realize my new boat with the tailless boot, and then after tuning the boat I realize a tail to overlap the boot so as to consider the aerodynamic effects.

What do you say?

But now I ask you to answer only a dry question,
the tips of the boots and the tip of the central fuselage, do I make them pointed or rounded like the front of a wing profile?

answer me as a poll, point or round.

thanks to all for the interesting considerations,
I am still very interested in theoretical discussions, but I have to start the construction so I would opt for solution 2, to add in a second moment the additional appendix, if you want to make other theoretical considerations or you want to help me simulate everything I will be grateful.

Hi.
Lorenzo

 

[Fulvio Romano]

I think it's better, but the important thing is that it doesn't get caught in the water. the attack edge of the wing profile however has no relevance to the problem.

but can I ask why these objects have no keel? Who convinces them to go straight?

However, in principle, to increase hydrodynamic sustenance, reduce the wet surface, better exploit the residual energy of the "spruzzi", more so many other amenities, the ideal is to use skates and steps as in the attached figure.

Consider that the skates must be two on the side. to put four as in the figure structurally helps the bottom, but does not practically have hydrodynamic effectiveness

 

[lorenzoneri]

straight go thanks to the rudder shovel and thanks to a fin on the right boot.

I could make a skate by side at the outside end,
Thank you.
Could be an idea.