Calculation of downwash of helicopter

[Hoangthien]

Hi everyone,
I am doing the research on helicopter aerodynamics. By applying the blade element theory and momentum theory we can determine the induced velocity at the balde, and we knew that, at a distance very far below the rotor, the induced velocity is two time of the corresponding value at rotor disc. how can we determine the induced velocity at a certain distance below the rotor disc. For example, I have a rotor disc, whose diamter is 150mm, and I would like to calculate the induced velocity at the distance 60mm below the rotor disc, but I do not know how to solve this problem. Could you share with me your knownledge in this section. Thanks!

 

[Aaron Bex]

There are various methods that can be used to calculate the induced velocity at a certain distance below the rotor disc. One of the most common methods is to use a mathematical model of the blade element theory and momentum theory. This model takes into account the airfoil shape of the blades, the rotor speed and the local flow properties. This model can then be used to calculate the induced velocity at a certain distance below the rotor disc. Additionally, it is also possible to use computational fluid dynamics (CFD) simulations to calculate the induced velocity. CFD simulations provide more accurate results than the mathematical models, but they require more computing power and time.

 

[ravenprp]

Hello,

Calculating the downwash of a helicopter involves understanding the aerodynamics of the rotor blades and the airflow they generate. The induced velocity at a certain distance below the rotor disc can be determined by using the momentum theory and the blade element theory.

Firstly, the momentum theory states that the downward flow of air caused by the rotor blades must equal the amount of lift generated by the blades. This means that the induced velocity, or the downward flow of air, is directly proportional to the lift force. Therefore, by knowing the lift force at a certain distance below the rotor disc, we can calculate the induced velocity.

Secondly, the blade element theory takes into account the varying lift and drag forces along the length of the rotor blade. This theory allows us to calculate the lift force at different points along the blade, and therefore, the induced velocity at different distances below the rotor disc.

To determine the induced velocity at a specific distance below the rotor disc, you will need to use the blade element theory to calculate the lift force at that distance. This can be done by dividing the rotor disc into smaller sections and calculating the lift force at each section. Then, using the momentum theory, you can determine the induced velocity at that distance.

In your example, you have a rotor disc with a diameter of 150mm and you want to calculate the induced velocity at a distance of 60mm below the rotor disc. You can use the blade element theory to divide the rotor disc into smaller sections, and then calculate the lift force at the section 60mm below the disc. Once you have the lift force, you can use the momentum theory to calculate the induced velocity at that distance.

I hope this helps to answer your question. Keep in mind that there are other factors that can affect the induced velocity, such as air density and rotor blade design. It may also be helpful to consult with experts in the field or refer to published research on helicopter aerodynamics for more accurate calculations. Good luck with your research!