Book contents
- Frontmatter
- Contents
- Preface
- 1Introduction
- 2Notation
- 3Hover
- 4Vertical Flight
- 5Forward Flight Wake
- 6Forward Flight
- 7Performance
- 8Design
- 9Wings and Wakes
- 10Unsteady Aerodynamics
- 11Actuator Disk
- 12Stall
- 13Computational Aerodynamics
- 14Noise
- 15Mathematics of Rotating Systems
- 16Blade Motion
- 17Beam Theory
- 18Dynamics
- 19Flap Motion
- 20Stability
- 21Flight Dynamics
- 22Comprehensive Analysis
- Index
- References
11 - Actuator Disk
Published online by Cambridge University Press: 05 May 2013
Book contents
- Frontmatter
- Contents
- Preface
- 1Introduction
- 2Notation
- 3Hover
- 4Vertical Flight
- 5Forward Flight Wake
- 6Forward Flight
- 7Performance
- 8Design
- 9Wings and Wakes
- 10Unsteady Aerodynamics
- 11Actuator Disk
- 12Stall
- 13Computational Aerodynamics
- 14Noise
- 15Mathematics of Rotating Systems
- 16Blade Motion
- 17Beam Theory
- 18Dynamics
- 19Flap Motion
- 20Stability
- 21Flight Dynamics
- 22Comprehensive Analysis
- Index
- References
Summary
The analysis of the wake is considerably simplified if the rotor is modeled as an actuator disk, which is a circular surface of zero thickness that can support a pressure difference and thus accelerate the air through the disk. The actuator disk neglects the discreteness in the rotor and wake associated with a finite number of blades, and it distributes the vorticity throughout the wake volume. The actuator disk model is the basis for momentum theory (sections 3.1.1 and 5.1.1). The simplest version of vortex theory uses an actuator disk model, which produces a tractable mathematical problem, at least for axial flight (section 3.7). In contrast to hover, the mathematical problem in forward flight is still not trivial, because of the skewed cylindrical geometry (section 5.2). Some results from actuator disk models were presented in section 5.2.1.
The focus of this chapter is the unsteady aerodynamics of the rotor associated with the three-dimensional wake. In particular, the dynamic inflow model is developed. This is a finite-state model, relating a set of inflow variables and loading variables by differential equations. Such a model is required for aeroelastic stability calculations and real time simulation. Vortex theory uses the Biot-Savart law for the velocity induced by the wake vorticity. Potential theory solves the fluid dynamic equations for the velocity potential or acceleration potential.
Vortex Theory
For the actuator disk in axial flow, the wake is a right circular cylinder (Figure 11.1). With uniform loading, the bound circulation is constant over the span, and the trailed vorticity is concentrated in root and tip vortices.
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- Rotorcraft Aeromechanics , pp. 414 - 441Publisher: Cambridge University PressPrint publication year: 2013
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