Prediction of Flow Pattern of Laminar Express Over a Full Rotation: Post 30

[If you are new to our measurements, you may take a minute to read here about vorticity (the colors in our plots), boundary layer separation and wakes]

We have recently tested some non-spinning MLB balls in orientations that are important to the “Laminar Express” pitch, which is a 2-seam fastball with some gyro component added, as show in Figure 1, viewed from above.

Figure 1: Sketch of a Laminar Express pitch as thrown by a right hander viewed from above in a single orientation

This is a unique pitch for which the orientation of the seams plays a role other than how the ball comes off the pitcher’s fingers. We have confirmed that the flow does look like that when the ball is in that orientation.

Figure 2: Non-spinning 90 mph 2019 MLB ball.

One thing you often hear about mechanical engineers is that they are able to visualize 3D space well. I am an exception to that rule, so I decided to take a brute force approach to visualizing the other orientations of this pitch. I asked our technician to drill a hole through a ball and put a rod in it.

Figure 3: Model ball.

I put the rod in a drill, rotated the ball to 9 positions, and took a snap of each. Then, I added sketches of the separated boundary layers from both sides of the ball. Here’s the scheme I used:

  1. The flow is “quasi-steady,” meaning that the rotating ball behaves like a series of non-rotating balls (not including the Magnus force, which is in the other plane).
  2. If there is a seam upstream of the hemisphere line on a given side of the ball, the flow will be turbulent. In the absences of a seam on the rear of the ball on that side, the boundary layer will separate about 30-40 degrees past the hemisphere line.
  3. If there is a seam upstream of the hemisphere line on a given side of the ball and a seam on the rear of the ball between 0 and 40 degrees past the hemisphere line, the boundary layer will separate off the rear seam.
  4. If there is no seam on a given side of the ball in front of the hemisphere line, the boundary layer will separate while laminar near the hemisphere line.
  5. The tilt of the wake is due to a pressure difference between the two sides, and such a difference exists if the separation point is different on the two sides. The lower the left side separation point is relative to the right one, the more tilt the wake gets. Which is the same as saying the more side force that is on the ball.
Figure 4: Animated Laminar Express, as thrown by a right hander, viewed from above.

There are 9 frames and 9 guesses as to the wake shape. Andrew Smith will be acquiring PIV data of each of them soon so we can learn if my 5 rules hold up.

Clearly, there is side force on the ball most of the time, and the force is to the left. Note that the pitch described as “Laminar Express” normally moves to the right, due to Magnus (most pitcher’s 2-seam has an axis tilted somewhat which adds a Magnus force in this plane). I claim that Magnus and the pressure force are competing on this pitch, and that absent spin (or with less spin) the ball would move left. I hope to demonstrate this soon.

One thing to note, while there are a couple of orientations where the boundary layer separation is laminar on one or both sides, there is little contribution to the side force from these. Again, I think the pitch is misnamed.

So, here, I’ve called my shot. We’ll see!

Apropos of nothing, here is a 2-seam splitter that breaks left.

(From Nathan Allan’s site)

Related Post

4 thoughts on “Prediction of Flow Pattern of Laminar Express Over a Full Rotation: Post 30

  1. If you go to figure !. in this post and keep the seam orientation the same but change the axis of spin to full gyro straight at the plate you would have seam in a substantial portion of the ‘horizon’. Similarly if you go figure 2. and rotate the ball about 10 degrees counter clockwise you would have a seam directly at the nose of the ball, a corresponding seam at the back of the ball and two seams at either side of the ball. Would the ‘long’ seams at the side in that area produce maximum stream separation and turbulence, that would result in less drag and slow the loss of velocity on the way to the plate? Such an effect would not result in a speed increase but in a slower loss of velocity. If such an effect did exist it could not be measured with a speed gun and would therefore go unnoticed. Might this the proverbial ‘sneaky fastball’?

    1. So, point the axis straight at the plate? That will result in turbulent flow everywhere nearly all the time with a seam on the front. This would be a low drag configuration, but I don’t think drag is very important to pitching.

      On your second point, I believe you are describing the orientation in Set 2 or 3 here:

      Those actually result in maximum drag (at least on a ball with a typical non 2019 seam) due to early boundary layer separation.

      Thanks for the interesting discussion.

Leave a Reply