NOTE: The conclusions drawn in this post are based on an erroneous idea about the orientation of this pitch (Figure 4). For the correct ball orientation, this description does not make sense. For a better explanation, see the new post
Let me say something important first. This is a fascinating pitch. Understanding it is going to require a bit of effort on your part, but I can assure you that your friends will be impressed and everyone will want you at their party.
I think it may be helpful to combine several posts on this site, add some new diagrams and make an end-to-end explanation of how this pitch works. This is one-stop shopping.
First, note that, to my knowledge, all pitches except knuckleballs and the Laminar Express generate movement primarily due to the Magnus effect, which is a force on a spinning moving object. Magus explains fastballs, curves, sliders, and changeups, and many pitching diagnostics, such as Rapsodo, assume Magnus effect is the only thing happening.
The notion of the pitch termed “Laminar Express” by Trevor Bauer is that one side of the ball has a laminar flow boundary layer while the other has turbulent flow. I’ll explain why this would matter below.
Understanding this phenomenon requires that you understand all of the following (no skipping)
- Baseball seams are disturbances to the flow over the ball
- The air velocity over the ball changes around the ball leading to
- Changes in the pressure on the ball which create
- Pressure gradients, or “hills” that can stabilize (keep laminar) or destabilize (make turbulent) the flow and that
- The effect of a seam depends on where it is relative to the pressure hills
- Laminar boundary layer separation makes a bigger wake than turbulent.
- 2-Seam pitches with a rotation axis perpendicular to flight direction (no gyro) always cause transition to turbulence.
- A small component of gyro spin can move seams out of any unforgiving areas allowing laminar flow on one side of the ball.
1) Seams are disturbances
When the flow over a surface is disturbed by a bump, it may cause laminar flow to become turbulent. It may also cause an attached boundary layer to separate.
2) Air velocity changes over the ball lead to 3) Changes in pressure
Below, I’ve drawn a ball moving right to left at speed Vball. The air velocity far away from the ball is zero. The air right in front of the ball is moving close to the ball speed. In an idealized situation called “potential flow,” the boundary layer remains attached and the air velocity at the back of the ball is also the ball velocity. (I will deal with a more realistic situation a little farther down). Because the air needs to accelerate (backwards) a lot to get around the ball, the air speed at the top of the ball is equal and opposite the ball speed.
The green curve is my sketch of what the air velocity looks like at different points around the ball. The well-known Bernoulli effect tells us that for flow past a stationary sphere, as the velocity gets larger, the pressure gets smaller. However, for a moving sphere in stationary flow, the result is different, as described here and shown below.
4) Pressure Hills
The important part of this picture is the pressure. Actually, the magnitude of pressure is not very important, but it is extremely important if the pressure is going uphill or downhill. Pressure going up is called “forgiving” while pressure going down is “unforgiving.” (Fluid dynamicists use the terms favorable or unfavorable gradient). If you disturb the flow while the pressure hill is forgiving, it returns to its original condition. The more forgiving it is (the steeper the pressure curve), the better the chance that the flow forgets about the seams.
It is easy to see in the pressure plot above that the flow is very forgiving at the front of the ball and becomes less so as we get close to the top/bottom of the ball. The rear of the ball is unforgiving, some of it very strongly so.
In fact, this is why the idealized “potential flow” sketched above does not exist. The boundary layer cannot remain attached in the unforgiving pressure region. A more realistic sketch is shown below.
As soon as the pressure hill becomes unforgiving, the boundary layer separates and a wake is formed. Note that the velocity and pressure on the front of the ball are unchanged, but the back is very different. Now it is easy to see that the pressure on the front of the ball is high and lower on the back. This is drag force on the ball and causes it to slow down (it’s not due to friction, as most people think).
5) The effect of a seam depends on where it is
Above, we have shown that disturbances in some places don’t do anything while if it is in an unforgiving location, even a small disturbance can have a big effect .
Seams near the front of the ball will have no effect due to the strong forging nature of the flow there. Less obviously, seams on the back of the ball have no effect because they reside in the wake (i.e. the boundary layer has already detached form the ball).
6) Laminar boundary layer separation makes a bigger wake than turbulent.
I find that many people understand that golfballs are dimpled to cause the flow over them to be turbulent, which makes the wake smaller and the drag smaller. But most have not had an opportunity to see the difference between a laminar and turbulent boundary layer separation. An important factoid: a turbulent boundary is more able to remain attached in an unforgiving area than a laminar boundary layer. I’ll use the Knuckleball PIV data shown below to illustrate. This ball is moving right to left.
The separation on the top of the ball was turbulent, and the boundary layer remain attached well into the unforgiving region past the center of the ball. The boundary layer was laminar on the bottom, and the separation happens sooner leading to a wake that is much larger on the bottom side.
For a knuckleball, the situation show above happens randomly and cannot be controlled. The Laminar Express seeks to create the same situation in a controllable way.
7) 2-Seam pitches with a rotation axis perpendicular to flight direction always cause transition to turbulence on all sides.
We know this empirically. I do not think it can be proven. My lab and others have tried and failed to show any effect of the seam orientation for pitches with no gyro* component. (See https://www.baseballaero.com/category/2v4/). It appears that even though the sides of a 2-seamer are smooth near the hemisphere of the ball, the flow at the seam locations is not sufficiently forgiving to remain laminar.
8) A small component of gyro spin can move seams out of any unforgiving areas allowing laminar flow on one side of the ball.
This is the amazing part. Most amazing of all is that this fact relies on the design of a baseball. A somewhat different seam pattern would eliminate this possibility. It’s also amazing to me that someone thought about adding gyro on purpose.
The sketch below shows a 2-seam pitch thrown by a right hander, moving right to left. It is viewed from above. Note the small gyro component (evidenced by the tilted axis). As you can see in the sketch, this tilt brings the seam on the front, 1st base side forward, into a more forgiving region. Meanwhile, the seam on the front of the ball on the 3rd base side is moved into a less forgiving region. This makes the 1st base side more likely to be laminar while the 3rd base side is more likely to be turbulent. If the two boundary layers are different, a sideways force results and the ball runs.
The PIV dataset shown below (ball moving left to right, sorry) has a laminar boundary layer on the top of the image (left side in the video) and turbulent on the other side. It has a force on it toward the right in the video.
What does it look like?
I’m still trying to train myself to spot it. The high-speed video above should be helpful, but the angle you see on TV is usually from the right of the pitcher, which changes things a bit.
The pitch should run, usually to the arm side, which is the same as the direction Magnus is driving the ball.
But (there is always a big butt, as noted by Pee Wee), some seem to be able to make it run the other way. Unfortunately, we can’t see the seams on the pitch below. It also appears to be a slider grip.
Harder for me to explain is this split finger pitch by Freddie Garcia taken from Rod Cross’s article, which is the one that launched me on this quest in the first place. Note how surprised the catcher is.
I started into this because I was trying to understand why a 2-Seam pitch behaved differently than a 4-seam. I concluded it did not unless the spin axis was modified at release.
But, while attempting to understand, I ran across explanations (mostly wrong) that discussed laminar and turbulent flow. In many cases, these were people who had caught wind of what Mr. Bauer was suggesting but didn’t fully understand it.
I’ve heard claims that some pitchers throw this pitch without trying or even realizing it. And that is not hard for me to believe. Could this be the secret of Bartolo Colon?
My interest was in the subtle, rich fluid dynamics interaction of disturbances, pressure gradients, boundary layer separation, and the weird, unique ways that baseballs are stitched. Do you realize after reading this that the pitch completely relies on a ball design that had nothing to do whatever with aerodynamics?
*Gyro: for you non-Pitcher Ninja types, “Gyro” spin means spin on an axis that is parallel to the direction of travel of the ball. Pure gyro spin would mean that the ball is spinning like a bullet. If viewed from above, any pitch for which the ball axis is not a line perpendicular to the direction of travel has a gyro component. Gyro spin does not contribute to the Magnus effect, and is therefore normally considered undesirable.