Experimental studies of the flow topology, leading-edge vortex dynamics and unsteady force produced by pitching and plunging flat-plate aerofoils in forward flight at Reynolds numbers in the range 5000–20 000 are described. We consider the effects of varying frequency and plunge amplitude for the same effective angle-of-attack time history. The effective angle-of-attack history is a sinusoidal oscillation in the range $\ensuremath{-} 6$ to $2{2}^{\ensuremath{\circ} } $ with mean of ${8}^{\ensuremath{\circ} } $ and amplitude of $1{4}^{\ensuremath{\circ} } $. The reduced frequency is varied in the range 0.314–1.0 and the Strouhal number range is 0.10–0.48. Results show that for constant effective angle of attack, the flow evolution is independent of Strouhal number, and as the reduced frequency is increased the leading-edge vortex (LEV) separates later in phase during the downstroke. The LEV trajectory, circulation and area are reported. It is shown that the effective angle of attack and reduced frequency determine the flow evolution, and the Strouhal number is the main parameter determining the aerodynamic force acting on the aerofoil. At low Strouhal numbers, the lift coefficient is proportional to the effective angle of attack, indicating the validity of the quasi-steady approximation. Large values of force coefficients (${\ensuremath{\sim} }6$) are measured at high Strouhal number. The measurement results are compared with linear potential flow theory and found to be in reasonable agreement. During the downstroke, when the LEV is present, better agreement is found when the wake effect is ignored for both the lift and drag coefficients.

An experimental investigation was performed on a nominally two-dimensional pitching and plunging SD7003 and flat plate at Reynolds number 1 × 10 4 , 3 × 10 4 , and 6 × 10 4. The experiment was conducted at the University of Michigan water channel facility using phaseaveraged particle image velocimetry (PIV) technique to quantify the flow field. Two sets of airfoil kinematics were used in this study; a combined pitching and plunging motion, and a pure plunging motion. The flow topology and wall velocity profiles from the PIV measurements showed a Re dependence on a pitching and plunging SD7003 where the extent of flow separation is reduced at a relatively high Re. On the contrary, flat plate displayed a large leading edge separation flow characteristic that was independent of Re. For both airfoil cross-sections used in the experiment, turbulence statistics indicated laminar to turbulent transition phenomena at low Re. The study shows the leading edge shape effect on the flow transition and separation characteristics. A pure plunging motion of SD7003 and flat plate at Re = 60,000 showed the formation of the leading and trailing edge vortices. In addition, a quantitative analysis showed an apparent phase lag present on SD7003 relative to the flat plate. In order to validate the experimental data, a flow comparison between the University of Michigan and AFRL was performed.

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An experimental investigation of pitching and plunging flat plate at a prescribed effective angle of attack in the St range of 0.16 to 0.32 and k range of 0.5 to 1.0 is presented. Force measurements and PIV technique were used to analyze and quantify the unsteady flow field created by the wing kinematics. A momentumbalance based non-intrusive force measurement technique and a systematic vortex detection algorithm were successfully implemented as a post-processing for PIV data to gain insight on the interplay between the unsteady force generation and vortex dynamics. It was determined that the inertial effects, which are proportional to the St, dominate the unsteady force generation while the differences in the force generation for the same St kinematics are contributed by the circulatory effects such as the size and location of the leading edge vortex. The normal force with respect the flat plate was the primary contributor to the lift and drag production, and the projection of the normal force due to high pitch amplitude at higher St prompted higher thrust generation. Nomenclature Geometric angle of attack [rad or °] 0 Mean angle of attack [rad or °] eff () t Effective angle of attack [rad or °] plmax Maximum plunge angle of attack [rad or °]

We consider a combined experimental (two-dimensional particle image velocimetry in a water tunnel) and computational (two-dimensional Reynoldsaveraged Navier-Stokes) investigation to examine the effects of chord Reynolds number on the dynamics of rigid SD7003 airfoil undergoing pitching and plunging motion in nominally two-dimensional conditions. Appreciable qualitative distinction in a moderately dynamically-stalled case in going from Re = 1×10 4 to Re = 6×10 4 was observed, suggesting nontrivial impact of viscosity even in conditions of strong forcing by motion kinematics. Additionally, computed lift coefficient time history is compared with Theodorsen's unsteady linear airfoil theory. The velocity and vorticity fields were in excellent agreement between experiment and computation for those phases of motion where the flow was attached; moderate agreement was achieved when the flow was separated. The small disagreements were consistent with the expected inaccuracies due to the turbulence model used. Similarly, Theodorsen's theory was able to predict the computed lift coefficient quite well when the flow was attached, and moderately acceptable otherwise. Nomenclature A = pitch amplitude, in degrees C L = airfoil lift coefficient per unit span c = airfoil chord (=152.4mm) f = airfoil oscillation pitch/plunge frequency

An experimental study of pitching and plunging airfoil at Re = 10,000 and pure sinusoidal effective angle of attack motion is presented in this paper. The experiments were conducted at the University of Michigan low-turbulence water channel facility using 2D phase-averaged particle image velocimetry (PIV). The effect of non-dimensional parameters governing pitching and plunging motion such as Strouhal number (St), reduced frequency (k), and the plunge amplitude (h 0) is investigated for the same effective angle of attack kinematics. The formation of a leading edge vortex (LEV) and a trailing edge vortex (TEV) is observed for all the cases studied. The formation phase of the LEV was found to be dependent on k; the LEV formation is delayed for higher k value. It is found that for cases with the same k the velocity profiles normal to the airfoil surface closely follow each other in all cases independent of pitch rate and pivot point effect. Analysis on the locations of the LEV core based on the Q-criterion and local streamline patterns helps identify the trajectory of the LEV core with respect to the airfoil. Additionally, a trend in the LEV circulation was observed. Nomenclature

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