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To investigate the flow control characteristics of antiphase pulsed jet technology and explore a more efficient method to control unsteady flow with minimal impact on flow turbulence, wind tunnel experiments were conducted. The aim was to address the issue of flow separation control on the surface of a cylindrical model. The model had a diameter of 100 mm, and an experimental setup utilizing an antiphase pulsed jet excitation was developed. The optimisation of unsteady jet control involved adjusting parameters such as jet momentum coefficient, slot position, and excitation frequency. The flow separation control effect on the cylinder surface was compared between in-phase and antiphase pulsed jet using a particle image velocimetry (PIV) technique. The mechanisms of flow control for these two methods were analysed. The results showed that in still air, increasing the jet momentum led to a gradual decrease in the high-velocity region, which also moved away from the wall. Under incoming flow conditions, positioning the slot closer to the separation point resulted in better flow separation control, particularly when the excitation frequency matched the main flow frequency. Both in-phase and antiphase pulsed jet excitations effectively suppressed flow separation. In the near-wall region within the symmetric plane between the two slots, the antiphase excitation reduced the root mean square of velocity fluctuations by approximately 1.9% and increased the average velocity by approximately 15.5% compared to in-phase pulsed jet excitation. In-phase pulsed jets exhibited low-frequency, high-velocity characteristics near the separation point, while antiphase pulsed jets, due to the alternating discharge of the two jets, had a lesser impact on the flow field turbulence. [ABSTRACT FROM AUTHOR]

Featured Application: The present study can be used for the development of high-lift flow-control devices for future civil aircraft. To provide sufficient lift during takeoff and landing, large aircraft are equipped with complicated high-lift devices. The use of simple flaps coupled with active flow control (AFC) can achieve lift improvement while reducing mechanical structure and weight. The present study focuses on verifying the feasibility and effectiveness of simple flaps combined with sweeping jet flow control. An experimental study on the AFC of flaps, using sweeping jets, was carried out using a NASA SC(2)-0410 supercritical airfoil wind-tunnel model at Re = 2.0 × 105 (with velocity V = 10 m/s). In the experiment, the wing angle of attack (α) ranged from 3 to 18°, and the flap deflection angle (δ) ranged from 0 to 30°; the aerodynamic characteristics and surface pressure characteristics of the wing at typical working conditions were analyzed. Using sweeping jets to control the flow on the flaps, the momentum coefficients (for three actuator groups) of the jet are 0.8%, 3.6%, and 8.2%, respectively, and the maximum lift coefficient was increased by approximately 33%. The influence of the sweeping jet flow rate on the aerodynamic performance of the airfoil is analyzed. There are two main reasons for the lift coefficient increase caused by sweeping jet flow: an extra suction peak near the flap and a suction peak increase near the leading edge area caused by induced flow. [ABSTRACT FROM AUTHOR]

Combined blowing was performed on a Hybrid Wing Body (HWB) aircraft through wind tunnel testing at a Reynolds number of 1.75 × 106. The full cycle of separation and reattachment under the control of combined blowing was implemented using Computational Fluid Dynamics (CFD), and the mechanism of combined blowing inhibiting separation was analyzed. The aerodynamic characteristics of the baseline and the independent effects of the blown deflected trailing edge (TE), blown leading edge (LE), and combined blowing on the TE and LE were investigated. The results clearly show that combined blowing can inhibit the development of cross-flow, reduce the accumulation of a boundary layer at the tip, and inhibit the flow separation effect. The effect of using seamless simple flaps alone to increase the lift is limited; blowing control is required to enhance the lift further. Applying the blown deflected TE can improve the lift linear segment, so that 30° flap achieves the lift gain of 40° flap without control, while the drag coefficient is approximately 0.02 smaller, but the stall gradually advances. Using the blown LE can significantly increase the stall angle from 12° to 18°. However, the lift linear segment remains unaffected. In particular, combined blowing can achieve the control effect of improving the lift linear segment, delaying stall, and decreasing drag. Moreover, the maximum lift coefficient is approximately 0.19, and the lift-to-drag ratio increment in the control state with a 30° flap deflection angle is above 2.2 in the angle of attack range of 4° to 12° compared to the uncontrolled state with a 40° flap deflection angle. [ABSTRACT FROM AUTHOR]

The characteristics and control of a wingtip vortex are of great significance when considering drag reduction and flight safety of transportation aircrafts. The associated aerodynamic phenomenon resulting from rolling up of a wingtip vortex includes boundary layer flow, shear layer separation, and vortex breakdown, while the interaction of a wingtip vortex with the airframe causes induced drag, wingtip noise, etc. This paper studies a normal blowing method utilized to control the wingtip vortex. Large eddy simulation (LES) technique applied to a straight NACA0012 wing having a chord length (c) of 0.4 m is adopted for this study. The Reynolds number based on the chord length is 1.6 × 10 6 and the angle of attack is 12°. The computational approach utilized the dynamic Smagorinsky-Lilly subgrid model for 3D simulations. Normal blowing from a high aspect ratio jet from the wingtip lower surface was used to control the wingtip vortex. From 0.05c to 0.30c, the blowing slit width was 1 mm, with the slit exit treated as a velocity inlet boundary condition which supplied the blowing jet with a momentum coefficient of 0.28%. Results of axial velocity and span-wise pressure distribution of the clean airfoil presented good agreement with known experimental data. LES results indicate that normal blowing suppresses the primary vortex strength, while the vortex core radius, maximum induced velocity, axial vorticity flux, and pressure peak of the primary vortex are reduced by 25%, 28%, 46%, and 52%, respectively. Flow field structures before and after blowing show that blowing suppresses the shedding, coiling, and convergence of the free vortex layers near the primary vortex. This study also shows that normal blowing generates a jet-induced vortex at the location of the secondary vortex, while backflow, volume expansion, and spiral burst can be observed in the jet-induced vortex. The bursting jet-induced vortex destroys the jet-like flow structure of the primary vortex at the trailing edge. [ABSTRACT FROM AUTHOR]