Effect of Manufacturing Inaccuracies on the Wake Past Asymmetric Airfoil by PIV

Abstract

The effect of manufacturing geometry deviations on the flow past a NACA 64(3)-618 asymmetric airfoil is studied. This airfoil is 3D printed according to the coordinates from a public database. An optical high-precision 3D scanner, GOM Atos, measures the difference from the idealized model. Based on this difference, another model is prepared with a physical output closer to the ideal model. The velocity in the near wake (0–0.4 chord) is measured by using the Particle Image Velocimetry (PIV) technique. This work compares the wakes past three airfoil realizations, which differ in their similarity to the original design (none of the realizations is identical to the original design). The chord-based Reynolds number ranges from 1.6×104 to 1.6×105. The ensemble average velocity is used for the determination of the wake width and for the rough estimation of the drag coefficient. The lift coefficient is measured directly by using force balance. We discuss the origin of turbulent kinetic energy in terms of anisotropy (at least in 2D) and the length-scales of fluctuations across the wake. The spatial power spectral density is shown. The autocorrelation function of the cross-stream velocity detects the regime of the von Karmán vortex street at lower velocities.

Wake flow past an ALUTEC profile

“…This effect is displayed in figure 5 for single angle of attack α = 15 • , but for other angles this behavior is similar. This behavior is observed in the wake past airfoil [7][8][9] and even in grid turbulence [10].…”

Vorticity statistics in the near wake of asymmetric prismatic airfoil NACA 64-618 at negative angle of attack –10° at Reynolds numbers 1.6 ⋅ 104 and 1.6 ⋅ 105 in distance 0.0 – 0.4 × chord past trailing edge measured by Particle Image Velocimetry

“…Figure 2 shows the example of few instantaneous data and the mean vorticities in the four discussed cases. The airfoil realizations are denoted "naive", or case A in our work [8], and "processed", or case C in [8]. We see that both realization display similar topology at same Reynolds numbers, while the Reynolds number (controlled via velocity) has much stronger effect on the mean wake shape.…”

Hot-Wire Investigation of Turbulence Topology behind Blades at Different Shape Qualities

“…The aerodynamic balance was applied to estimate the effect of shape inaccuracy on the airfoil lift and drag forces [60]. Figure 20 The main structural parts of the balance are a resiliently suspended movable table and an eddy current sensor.…”