CORRECTION (0:57 to 1:30) for the picture on the right-hand side: 'laminar boundary layer' should be 'turbulent boundary layer'. For more information, visit https://www.airshaper.com or email [email protected] ---------------------------------------------------------------------------------------- In this video, we look at the aerodynamics of golf ball dimples and how to apply (or not apply) them to your design! Aerodynamics of a sphere A golf ball without dimples, a simple sphere, features attached, laminar flow at the front: as the air moves over the surface, a boundary layer of slower moving air grows thicker as it sticks to this surface. As soon as the flow goes beyond the halfway point and needs to contract, it becomes more & more difficult for the flow to stay attached to the surface and eventually. Separates, resulting in a detached flow. This creates a large wake behind the golf ball, which increases drag and slows it down. Aerodynamics of a golf ball with dimples When you apply dimples to the surface, the boundary layer becomes turbulent. It will mix with the surrounding air and retain more kinetic energy. This energy allows the airflow to stay attached further down the back of the golf ball, moving the separation location further downstream to reduce the size of the wake. These dimples may increase the friction drag a little but reduce the pressure drag so much that the golf flies roughly twice as far! Golf ball dimples on cars, golf ball dimples on planes, ... So does this mean we should cover every surface on every car or plane with dimples to make it more aerodynamic? No, not quite. It only makes sense to create a turbulent boundary layer just ahead of a separation location. Modern day cars for example, have such a sleek profile that they have attached flow all the way to the back of the car. And even at the back of the car, a turbulent boundary layer would still not be enough to make it follow the negative curvature at the end of the trunk. Golf ball dimples in sports Another example is to reduce drag around cylinders. There it does make sense, depending on the Reynolds number, to add roughness or dimples or what so ever, to move the separation location further downstream. But on a golf ball you have dimples everywhere because you don’t know the direction of the golf ball. On a cylinder, if the flow is coming always from the same direction, it makes sense to only add roughness just ahead of the separation location, so not at the rear of the cylinder where the flow is already detached. A practical example of this are the arms of an athlete or cyclist, where the wind always comes from the front or a slight angle of attack, so it makes sense to only add roughness just ahead of the separation location on the arms. This is something you already see on some outfits of the riders.