Modern Helicopter Aerodynamics

Abstract

▪ Abstract Modern helicopter aerodynamics is challenging because the flow field generated by a helicopter is extremely complicated and difficult to measure, model, and predict; moreover, experiments are expensive and difficult to conduct. In this article we discuss the basic principles of modern helicopter aerodynamics. Many sophisticated experimental and computational techniques have been employed in an effort to predict performance parameters. Of particular interest is the structure of the rotor wake, which is highly three-dimensional and unsteady, and the rotor-blade pressure distribution, which is significantly affected by the strength and position of the wake. We describe the various modern methods of computation and experiment which span the range from vortex techniques to full three-dimensional Navier-Stokes computations, and from classical probe methods to laser velocimetry techniques. Typical results for the structure of the wake and the blade pressure distribution in both hover and forward flight are presented Despite the complexity of the helicopter flow, significant progress has been made within the last ten years and the future will likely bring marked advances.

Lifting multi-blade flows with interaction

“…Section 4 presents computational results for the present multi-blade flows with various degrees of nonsymmetry, followed by an analysis for small ratios of blade length to wake length in § 5 which is motivated by the short-blade approach developed in and obtains explicit results for the surface pressures, the wake shape and the lift generated, for comparison. The theoretical results are remarkably similar to the experimental and numerical ones in Conlisk (1997, figure 8) mentioned previously. Section 6 provides further comments.…”

“…The jumps across the leading edge are apparent throughout, along with the boundary layer growth on each blade surface and the thin wake downstream. The above solutions for pressure in particular compare favourably in qualitative terms with the experimental and computational results in figure 8 of Conlisk (1997) for a lifting rotor in hover mode. The lift and drag for the flat-plate cases of figures 3-5 are given in figure 10 in scaled form, from integration of the surface pressure differences and the skin friction sums along the blade.…”

“…Theoretical works on multi-blade-wake interactions appear to be few, especially concerning boundary layers and allied features; see also Conlisk (1997). Smith & Timoshin (1996a) investigated three-dimensional rotating configurations of thin blades (such as for a cut disk) under the assumptions of normal symmetry and negligible motion far from the configuration, and pointed out a number of unusual viscous-inviscid properties that arise despite the imposed uniform surface pressure distributions in their cases.…”

Aerodynamically Efficient Rotor Design for Hovering Agricultural Unmanned Helicopter

“…A variety of numerical techniques can be utilized in making this assessment, ranging from the simplified momentum theory to direct modeling using advanced computational fluid dynamics (Miller 1985, Conlisk 2001, Leishman 2006, Johnson 2013. The methods based on the momentum theory are low-fidelity methods while for better accuracy, high-fidelity methods such as CFD are desired.…”

“…The primary design parameters for the helicopter are the dimensionless coefficients related to thrust and power (Conlisk 2001). These coefficients are: the thrust coefficient defined by…”