What is the magnus effect?

What is the Magnus effect?

Understanding Magnus Effect

Magnus Effect - Wikimedia

Magnus effect is one of the important effect to study in Aerodynamics. Magnus effect is an effect on on the rotating object placed in airflow due to its rotation. Let's discuss about Magnus effect.

Discovery: -

The Magnus effect is named after Heinrich Gustav Magnus, the German physicist who discovered it.

Heinrich Gustav Magnus - Wikimedia

Definition: -

Encyclopedia Britannica defines Magnus effect as follows

Magnus effect, generation of a sidewise force on a spinning cylindrical or spherical solid immersed in a fluid (liquid or gas) when there is relative motion between the spinning body and the fluid.

Oxford Dictionary defines Magnus effect as

The force exerted on a rapidly spinning cylinder or sphere moving through air or another fluid in a direction at an angle to the axis of spin. This force is responsible for the swerving of balls when hit or thrown with spin.

Explanation: -

Consider streamline airflow over simple stationary cylinder

Airflow over stationary cylinder - Wikimedia

Airflow will simply go around the cylinder as shown in figure above.

Now, Check out the airflow over rotating cylinder

Airflow over rotating Cylinder - Wikimedia

(Consider left side of image is front of the cylinder and right side of the image is back of the cylinder)

When Airflow hits rotating cylinder, velocity of the air will increase in the direction of the rotation of the cylinder due to friction between surface of the cylinder and the air. In the figure above, cylinder is rotating in the clockwise direction. So due to friction, cylinder will throw the air backwards. This increases the velocity of the air at the backside of the cylinder. As we know according to Bernoulli's principle higher the velocity, lower the pressure. Hence, Increased velocity behind the cylinder will reduce the pressure behind it(cylinder). And due to pressure difference between front and back of the cylinder, cylinder will move backwards (Towards the region with less pressure). This effect is known as Magnus effect.

Application of the Magnus Effect: -

Flettner aircraft: - A flettner aircraft is a type of aircraft which uses a Flettner rotor to provide lift. The rotor consists of a spinning cylinder with circular end plates and it spins about a spanwise horizontal axis. Magnus effect creates lift.