THEORETICAL ANALYSIS WITH CFD RESULTS
1 The theoretical analysis has been done with the available data and parameters given for Bell 412 helicopter. Bell 412 flying manual was used as reference for data. Two main theories named Blade Element Theory and Momentum Theory were used for rotorcraft calculations. Many assumptions were taken for rotorcraft calculations and simulation.
ASSUMPTIONS
• The 1:1 solid model was modeled for the three simulations set up according to the dimensions provided by the Bell 412 flying manual. Since main rotor was taken as isolated main rotor, analysis and considerations based only on the main rotor. We assumed that no any effect occurred due to the tail rotor motion, weight and fuselage drag effects.
• For calculations empty rotor craft weight was taken. But in CFD simulations no any weight was considered. So, power calculations cannot be made for the model main rotor except the flow pattern analysis. Model main rotor was considered isolated and free from the weight effects from the airframe structure.
• Standard atmospheric conditions were assumed for all three flight maneuvers. Inlet flow velocity values have taken as 35 m/s for forward flight and 0 m/s for hovering and HIGE/ HOGE.
• Air was assumed to be inviscid and incompressible.
• The rotor was assumed to act as a uniformly loaded disk or an actuator disk. This Implies rotor has an infinite number of blades.
• The flow both upstream and downstream of the disk was assumed to be uniform and occurred at constant energy.
• No rotation is imparted on the fluid by the action of the rotor.
• Rotor is modeled as wings which are rotating around a central mast.
7.1 MOMENTUM THEORY
2 Momentum theory was initially developed for studying propellers and then applied to helicopter propellers. The helicopter rotor can be idealized as a momentum disk. It imparts a uniform velocity (vi) to the airflow creating a change in momentum which will result in an upward thrust (T).
There are key assumptions made to apply momentum theory:
1. Air is inviscid and incompressible.
2. The rotor act as a uniformly distributed disk or as an actuator disk.
Implies rotor has an infinite number of blades thus no periodicity in the wake.
3. The flow both upstream and downstream of the disk is uniform, occurs at constant energy.
4. No rotation is imported on the fluid by the action of the rotor.