Numerical Investigation of Frequency and Amplitude Influence on a Plunging NACA0012

Abstract

Natural flight has always been the source of imagination for Mankind, but reproducing the propulsive systems used by animals that can improve the versatility and response at low Reynolds number is indeed quite complex. The main objective of the present work is the computational study of the influence of the Reynolds number, frequency, and amplitude of the oscillatory movement of a NACA0012 airfoil in the aerodynamic performance. The thrust and power coefficients are obtained which together are used to calculate the propulsive efficiency. The simulations were performed using ANSYS Fluent with a RANS approach for Reynolds numbers between 8500 and 34,000, reduced frequencies between 1 and 5, and Strouhal numbers from 0.1 to 0.4. The aerodynamic parameters were thoroughly explored as well as their interaction, concluding that when the Reynolds number is increased, the optimal propulsive efficiency occurs for higher nondimensional amplitudes and lower reduced frequencies, agreeing in some ways with the phenomena observed in the animal kingdom.

Plunging Airfoil: Reynolds Number and Angle of Attack Effects

“…At Re = 3 × 10 6 , the maximum propulsive efficiency reached values close to 0.75 but with considerably low thrust coefficient values. The same effect was previously observed by Camacho et al [5,22] for a Reynolds number of 3.4 × 10 4 .…”

“…The present methodology was previously described in detail in [5] and only the main points will be mentioned here. Mesh and timestep independence studies were conducted for a Re = 1.7 × 10 4 , k = 2.5, and h = 0.5 and during the simulation, due to the turbulence model requirements, the y + was maintained under 5.…”

“…In this subsection, the relationship between mean thrust and power requirements is explored. For this analysis, the previously obtained data in [5] was used, which consisted of analyzing the aerodynamic and propulsive characteristics of a NACA0012 plunging airfoil at three different Reynolds numbers (8.5 × 10 3 , 1.7 × 10 4 , 3.4 × 10 4 ), reduced frequencies between 1 and 5, and a nondimensional amplitude never exceeding 0.5.…”

“…Nonetheless, the unsteady airfoils study is also helpful concerning aeroelastic analysis [2,3] and dynamic stall, which negatively affects helicopter rotors [4]. Lately, the study of oscillating airfoils lost focus on their propulsive capabilities but is rather exploring their potential to extract energy from the flow field [5].…”

“…Nevertheless, at a Reynolds number of 2 × 10 4 Platzer et al [16] states that operating at high frequency and low amplitude would favor the propulsive efficiency. In fact, the flapping airfoil problem is highly affected by the governing parameters as seen in [5,22] where the maximum efficiency zone is a clear function of the Reynolds number.…”