Prescribed-wake particle model · momentum-theory inflow · helical tip filaments
Each particle represents a small parcel of air. The rotor accelerates it downward, creating an induced velocity field — the wake. This model prescribes the geometry of the tip vortices (the concentrated swirling filaments shed from each blade tip) and fills the disk with an inboard vortex sheet that captures the radially-varying bound circulation.
The color maps swirl velocity magnitude |vθ|: blue is quiescent air, red-orange marks the cores of the tip vortices where velocities peak. The gradient reveals the radial structure of the wake — strong tip filaments flanking a weaker inboard sheet.
In hover (V = 0) the wake contracts axially below the rotor — the slipstream narrows as momentum builds. The contraction ratio approaches ~0.7 at full development. Tip vortices stack in tight helices that mutually interact and drive the instability responsible for blade-vortex interaction (BVI) noise on descent.
Add forward airspeed and the entire wake skews aft. The retreating-side vortices convect away quickly while the advancing-side vortices remain close to the rotor plane longer, increasing the asymmetric inflow that produces dissymmetry of lift. By cruise speed the wake is fully blown aft and the inflow distribution becomes nearly uniform.
Descend at low forward speed (the region below and left on the power curve) and the rotor begins re-ingesting its own wake — vortex ring state. The wake state indicator will flag incipient VRS when the ratio of descent rate to induced velocity exceeds ~0.12. Developed VRS produces significant thrust fluctuation and loss of collective authority.
This is a reduced-order kinematic model, not CFD. Inflow uses momentum theory with Pitt-Peters corrections for skew angle. Tip vortex geometry follows a Landgrebe-style prescribed contraction and pitch schedule. Aeroelastics, fuselage blockage, and ground effect are not modeled. Amber readouts are estimated quantities.
Drag to orbit · scroll or pinch to zoom. Set V = 0 for hover. Raise V to skew the wake aft. Descend at low V to enter vortex-ring state. Switch between UH-60 and MV-75 rotor geometries using the selector in the top bar.
prescribed-wake particle model