Visualization of vortical flows around a rapidly pitching wing and propeller

Erlong Su, Ryan Randall, Lee Wilson, Sergey V Shkarayev

Research output: Contribution to journalArticle

Abstract

This study was conducted to visually investigate flows related to fixed-wing vertical-takeoff-and-landing micro air vehicles, using the smoke-wire technique. In particular, the study examines transition between forward flight and near-hover. The experimental model consists of a rigid Zimmerman wing and a propulsion system with contra-rotating propellers arranged in a tractor configuration. The model was pitched about the wing’s aerodynamic center at approximately constant rates using a five-axis robotic arm. Constant-rate pitching angles spanned 20° to 70°. No-pitching and four pitching-rates were used, along with three propulsive settings. Several observations were made during no-pitching tests. Turbulent wakes behind blades and laminar flow between them produces pulsations in the boundary layer. These pulsations alter the boundary layer from a laminar to turbulent state and back. An increase in lift and drag in the presence of a slipstream is a result of competing effects of the propulsive slipstream: (a) suppression of flow separation and increased velocity over the wing and (b) decrease of the effective angle of attack. Higher nose-up pitching-rates generally lead to greater trailing-edge vortex-shedding frequency. Nose-up pitching without a slipstream can lead to the development of a traditional dynamic-stall leading-edge vortex, delaying stall and increasing wing lift. During nose-up pitching, a slipstream can drive periodically shed leading-edge vortices into a larger vortical-structure that circulates over the upper-surface of a wing in a fashion similar to that of a traditional dynamic-stall leading-edge vortex. At lower nose-up pitching-rates, leading-edge vortices form at lower angles of attacks. As a slipstream strengthens, a few things occur: separation wakes diminish, separation occurs at a higher angle of attacks, and downward flow-deflection increases. Similar effects are observed for nose-up pitching, while nose-down pitching produces the opposite effects.

Original languageEnglish (US)
Pages (from-to)25-43
Number of pages19
JournalInternational Journal of Micro Air Vehicles
Volume9
Issue number1
DOIs
StatePublished - Mar 1 2017

Fingerprint

Propellers
Vortex flow
Visualization
Angle of attack
Boundary layers
Rigid wings
Micro air vehicle (MAV)
Fixed wings
Robotic arms
Flow separation
Vortex shedding
Takeoff
Landing
Laminar flow
Smoke
Propulsion
Drag
Aerodynamics
Wire

Keywords

  • Flow
  • Propeller
  • Visualizations
  • Wing

ASJC Scopus subject areas

  • Aerospace Engineering

Cite this

Visualization of vortical flows around a rapidly pitching wing and propeller. / Su, Erlong; Randall, Ryan; Wilson, Lee; Shkarayev, Sergey V.

In: International Journal of Micro Air Vehicles, Vol. 9, No. 1, 01.03.2017, p. 25-43.

Research output: Contribution to journalArticle

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