The one thing I didn't get is that the drift maximisation should occur when the boundary layer separation distance is maximum between both sides of the ball from each other, so it should be somewhere close to the top spinner, but in practice it is closer to the square spinner. So maybe the optimal width of wake formation and resultant reaction force is dependent on maximising the horizontal distance between both points which occurs closer to the square seam/rifle spin seam?
Another thing that can be inferred is, does this necessitates the seam to be upright and there wouldn't be much drift on the scramble seam even if the rotational axis is kept the same as Lyon's. Unlike for dip?
I agree. Top spinner, with seam near the front and rear of the ball, at say 20degrees seam angle, will behave like conventional swing (though at lower Reynolds number) - this often gets referred to as an arm ball. To get the seam to directly separate the boundary layer, we think the seam has to be close to the "shoulders" of the ball, i.e. at seam angle 70 or 80degrees. We're running wind tunnel tests to try to understand this further as it is just an hypothesis at the moment.
For the scrambled seam there is another story, closely linked to baseball aerodynamics, which we are also hoping to prove or at least understand better, with experiments in our tunnel.
I'd be really interested to see the difference between drift and dip for cross seam and 'with the seam' spin bowling.
Often people talk about drift being caused by the revs on the ball - which matches an understanding of drift based on the Magnus effect, an understanding which you seem to show is not the true driver of spinners' drift.
Interestingly, Murali one of the greatest turners of a ball did not drift the ball and mainly bowled cross seam. There are many spinners (especially SLAs) who seem to drift the ball miles, without really being great turners of the ball.
There is a great clip of Murali with Nathan Lyon on YouTube explaining that bowling with the seam gives drift and not much dip, whereas bowling cross seam gives dip but not drift. That certainly matches my experience of bowling leg spin, so would be interesting to know if that is backed up by the science!0
On the point about conventional swing for spinners, Lyon is a good example. When he bowls with a lot of overspin he frequently seems to drift the ball in the direction of conventional swing (i.e. in to the right handed) opposite of a usual offspinners drift!
Again, interested whether the arm ball (a mostly back spinning delivery) would be expected to drift in the same way as a mostly over spinning delivery with the same seam angle (so opposite rotation axis). Presumably yes given the effect is non-Magnus.
so if magnus doesn't explain drift of a spinner, how did Kuhnemman got reverse drift when operating at higher speeds?
The one thing I didn't get is that the drift maximisation should occur when the boundary layer separation distance is maximum between both sides of the ball from each other, so it should be somewhere close to the top spinner, but in practice it is closer to the square spinner. So maybe the optimal width of wake formation and resultant reaction force is dependent on maximising the horizontal distance between both points which occurs closer to the square seam/rifle spin seam?
Another thing that can be inferred is, does this necessitates the seam to be upright and there wouldn't be much drift on the scramble seam even if the rotational axis is kept the same as Lyon's. Unlike for dip?
I agree. Top spinner, with seam near the front and rear of the ball, at say 20degrees seam angle, will behave like conventional swing (though at lower Reynolds number) - this often gets referred to as an arm ball. To get the seam to directly separate the boundary layer, we think the seam has to be close to the "shoulders" of the ball, i.e. at seam angle 70 or 80degrees. We're running wind tunnel tests to try to understand this further as it is just an hypothesis at the moment.
For the scrambled seam there is another story, closely linked to baseball aerodynamics, which we are also hoping to prove or at least understand better, with experiments in our tunnel.
I'd be really interested to see the difference between drift and dip for cross seam and 'with the seam' spin bowling.
Often people talk about drift being caused by the revs on the ball - which matches an understanding of drift based on the Magnus effect, an understanding which you seem to show is not the true driver of spinners' drift.
Interestingly, Murali one of the greatest turners of a ball did not drift the ball and mainly bowled cross seam. There are many spinners (especially SLAs) who seem to drift the ball miles, without really being great turners of the ball.
There is a great clip of Murali with Nathan Lyon on YouTube explaining that bowling with the seam gives drift and not much dip, whereas bowling cross seam gives dip but not drift. That certainly matches my experience of bowling leg spin, so would be interesting to know if that is backed up by the science!0
On the point about conventional swing for spinners, Lyon is a good example. When he bowls with a lot of overspin he frequently seems to drift the ball in the direction of conventional swing (i.e. in to the right handed) opposite of a usual offspinners drift!
Again, interested whether the arm ball (a mostly back spinning delivery) would be expected to drift in the same way as a mostly over spinning delivery with the same seam angle (so opposite rotation axis). Presumably yes given the effect is non-Magnus.