Effects of steady wake-jets on subcritical cylinder flow

Abstract

We investigate the effects of active wake-jets (characterized by a dimensionless jet momentum coefficient C µ) on the suppression of aerodynamic forces and the manipulation of wake flow topology behind a cylindrical model through wind tunnel tests. The active jets are positioned at the rear stagnation points of the cylindrical test model. The experimental campaign is conducted at a subcritical Reynolds number of Re= 3.33 × 10 4. The surface pressure distributions around the bare and controlled cylinders are obtained by using a pressure measurement system. Apart from pressure measurements, we also obtain the streamwise and spanwise flow structures around the circular cylinder with different C µ (including C µ = 0) by employing the particle image velocimetry (PIV) technique. Pressure measurement results demonstrate that the lift force acting on the cylindrical test model is greatly reduced and drag decreased with the implementation of active wake-jets. Besides, it is found that a higher C µ contributes to a better control effectiveness in unsteady lift forces but not necessarily a better drag reduction. PIV measurement results indicate that the mechanism of the active jet control scheme is to impose steady and symmetric perturbations into the unsteady and asymmetric flows in the cylinder wake. Owing to the dynamic competition of the wake-jet flow and shear layer flows, the vortex shedding pattern behind the controlled cylinder is greatly modified, vortex formation length significantly elongated and the fluctuations of aerodynamic forces conceivably suppressed.

Experimental Investigation and Validation on Suppressing the Unsteady Aerodynamic Force and Flow Structure of Single Box Girder by Trailing Edge Jets

“…Obtaining better control effectiveness does not need larger non-dimensional jet momentum coefficients. There is an optimal non-dimensional jet momentum coefficient to realize the control effect, which is consistent with the study by Chen et al [20] and Gao et al [27].…”

“…Therefore, an optimal J sj for alleviating the unsteady aerodynamic force that is being exerted in the SBG model is required. This saturation phenomenon was also found by Chen et al [20], Gao et al [27], and Apelt et al [30]. When the J sj equals 0.0094, the best control ability was possessed in the present investigation.…”

“…Sci. 2022,12, x FOR PEER REVIEW 9 of 20 saturation phenomenon was also found by Chen et al[20], Gao et al[27], and Apelt et al[30]. When the Jsj equals 0.0094, the best control ability was possessed in the present investigation.…”

Vortex Shedding and VIV Suppression

“…As shown in Fig. 10, a nozzle is installed on the rear side of the cylinder (Feng et al 2010(Feng et al , 2011Gao et al 2019). By pumping extra fluid into the wake as a high-speed jet, the shear layers on both sides of the cylinder move toward the centerline to shift the boundary layer backward.…”

Cylinder flow and noise control by active base blowing

“…Their findings indicated that while slight blowing did not affect the shedding frequency, it was effective in stabilising the wake by reducing backflow and, consequently, decreasing absolute instability in the near-wake region. After a considerable lapse in this research domain, Gao et al (2019) conducted an experimental study to investigate the impact of base jets, emitted from four nozzles into the wake of a circular cylinder, on vortex shedding at Re = 3.33 × 10 4 . The experimental results demonstrated that distributing base jets along the span length of 3D altered the vortex-formation pattern and reduced both the drag and lift coefficients by introducing perturbations into the unsteady and asymmetric flows in the cylinder wake.…”