Dimpled Nosecone for Reduced Drag? No way...

[SolarYellow]

Had a thought. This might work on an Honest John to hold the boundary layer back down closer to the smaller diameter of the airframe. Might make the smaller fins on the later-developed version more effective for improved stability.

 

[schworer]

Gentlemen - for your reading pleasure, attached is the Masters Thesis " Aerodynamic Dimpling for the Nose Cone of a High-Power Competition Rocket" by Graham Monroe, December 2023, for a MS in Mechanical Engineering. I downloaded it from the UNM Digital Repository, I haven't had the time to read it over yet, but it contains details on the dimpled VK nose cone, modeling, and flight test data. Also linked is an article published on the Sandia Labs website on Dr. Sal Rodriguez, thesis advisor, with photos of the thesis author. BTW, Dr. Rodriquez has quite impressive academic credentials, BS - Nuke Engineering, MS - Mech Engineering, MS - Applied Math, PhD - Nuclear Engineering, PhD - Philosophy & Apologetics. He was just awarded Scientist of the Year at Great Minds in STEM.

https://www.sandia.gov/labnews/2024/01/25/changing-the-world-one-dimple-at-a-time/

 

[Rschub]

I read it, I still say a wind tunnel would give more repeatable and accurate results. There are too many "correction" factors in their experiment for me.
It's also possible that the dimples will not work in the southern hemisphere.
I also saw the word proprietary quite a few times....

 

[schworer]

You are probably right about using a wind tunnel. Re proprietary - well that goes along with being granted the patent.

 

[Rschub]

My only point is that if you are claiming results that no one else has been able to attain, as documented in this very paper, you need a more bullet proof experimental regimen. Particularly if money is involved.

 

[GlenP]

There may be some effects of a nose cone with golf ball type dimples on the overall airflow over the rocket and the base drag, sure.

However, the scale of dimples on a golf ball are not quite the best way to achieve the desired favorable effects as a “one size fits all” for all sizes of rockets of the typical configuration.

To achieve a turbulent boundary layer flow with better mixing closer to the surface which can help keep flow attached better over a reducer transition, boat tail, and keep the separated wake region at the base of the rocket smaller, ie all those considerations to keep the base drag as low as possible at the acceptable cost of a slight increase in skin friction drag, there are better alternatives to tripping the boundary layer from laminar to turbulent at an appropriate scale tailored for a particular rocket.

This technique is used routinely on scale models in wind tunnel tests to better approximate the behavior of a higher Reynolds number full scale flight vehicle in a wind tunnel at a model scale. Appropriately sized small “trip dots” are placed at strategic locations, scaled to the boundary layer height at the model scale. Not exactly the same concept as what are traditionally called vortex generators, those have a specific purpose and are much more aggressive, but the dots work in a similar but more subtle way. The strip of little short cylindrical or disc stickers almost have an appearance of a line of glue dots or simulated rivets on a steampunk rocket, for example. The size is tailored to the boundary layer.

Sure a dimpled nose cone might have some impact, but a better and more consistent result of the desired performance improvements can be obtained with an appropriately sized ring of trip dots around the body tube maybe a little farther down from the nose cone.

The appropriate size itself is a function of the Reynolds number, and the challenge there for a model rocket that is accelerating over a very wide range of speeds, is that those fixed parts of the structure will only be most effective at one small range of speeds that the rocket passes through for one short instant in the overall boost and coast phases, so, similarly to when you are stuck in a nebula and you can't lock on phasers, best guess Mr. Sulu.

 

[Rschub]

I have a method that I just thought up to reduce drag, I will get back to everyone once I have patented it. It involves the Krushnic effect, a long burn motor and thousands of tiny holes.

 

[kuririn]

I have a method that I just thought up to reduce drag, I will get back to everyone once I have patented it. It involves the Krushnic effect, a long burn motor and thousands of tiny holes.

Maybe gas dynamic stabilization in place of the Krushnic Effect?

 

[jqavins]

I used to watch WKRP and Les Nessman's pronunciation of Rodriguez still sticks with me.

Along with his pronunciation of Chi Chi. And, on a different occasion, chihuahua.

If dimples were so effective why has none of the big boys (NASA, SpaceX, etc) ever used them?

I'm guessing that with all those engineers for all those organizations they've already done the research and already come to the same conclusion.

You're probably right, but on the other had assuming things like that as a reason not to give it a try is a good way to stifle research.

Since the rocket is not spinning, the second reason for dimpling a golf ball does not apply.

That suggests that dimpling a boat tail would likely be more effective than dimpling a nose cone.

 

[jqavins]

If dimples were so effective why has none of the big boys (NASA, SpaceX, etc) ever used them?

I'm guessing that with all those engineers for all those organizations they've already done the research and already come to the same conclusion.

You're probably right, but on the other had assuming things like that as a reason not to give it a try is a good way to stifle research.

 

[DAllen]

You're probably right, but on the other had assuming things like that as a reason not to give it a try is a good way to stifle research.

As I said...its a guess not an assumption.

 

[aerostadt]

I'll tell you one thing. I have no plans to go out into my work shop and start pounding dents into all my nose cones.

 

[SolarYellow]

https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/drag-on-a-sphere/

Drag on a Sphere

All of the calculations shown for the cylinder have employed a smooth surface. But since drag depends on the flow in the boundary layer, we can expect some changes with surface roughness. It is observed experimentally that a roughened cylinder or ball will transition to turbulent flow at a lower Reynolds number than a smooth cylinder or ball. Drag for a rough surface ball is shown on the figure at the top of the page by the dashed line. This effect produces a rather interesting result. There is a small range of Reynolds numbers for which the drag of a roughened ball is less than the drag of a smooth ball for the same diameter, velocity and flow conditions. The size and speed of a golf ball falls within this Reynolds number range. That is why a golf ball has dimples; the roughened surface causes transition to turbulence that would not occur yet on a smooth golf ball. The lower drag on the dimpled golf ball allows the ball to fly farther than a smooth ball of the same speed, diameter and weight.

 

[cwbullet]

I'll tell you one thing. I have no plans to go out into my work shop and start pounding dents into all my nose cones.

Moat of the ones who experiment with this, make their own. Fiberglass or 3d printed are the one's I have seen.

 

[Buckeye]

Gentlemen - for your reading pleasure, attached is the Masters Thesis " Aerodynamic Dimpling for the Nose Cone of a High-Power Competition Rocket" by Graham Monroe, December 2023, for a MS in Mechanical Engineering. I downloaded it from the UNM Digital Repository, I haven't had the time to read it over yet, but it contains details on the dimpled VK nose cone, modeling, and flight test data. Also linked is an article published on the Sandia Labs website on Dr. Sal Rodriguez, thesis advisor, with photos of the thesis author. BTW, Dr. Rodriquez has quite impressive academic credentials, BS - Nuke Engineering, MS - Mech Engineering, MS - Applied Math, PhD - Nuclear Engineering, PhD - Philosophy & Apologetics. He was just awarded Scientist of the Year at Great Minds in STEM.

https://www.sandia.gov/labnews/2024/01/25/changing-the-world-one-dimple-at-a-time/

Thanks for sharing this. Looks like they are researching the dimples for friction drag reduction, which would be more applicable for a rocket nosecone.

The masters thesis was well done. I am saving this as a reference for backing out Cd from flight data.

The student had to wrangle through reconstructing the flight trajectory, air properties, and finding error in the accelerometer measuerements. These uncertanties cast some doubt on the conclusions, especially with the competing trajectory models showing opposite drag results. CFD or wind tunnel testing does not suffer from these things.

The advisor at Sandia has access to government lab wind tunnels and mega super-computing CFD. He didn't bother to do a dedicated aero study on this nose cone? The guy is walking around schools, conferences, and reporters with the thing under his arm, touting the Dimplizer. You would think his validation would be more rigorous.