In this paper, we use numerical simulation and dynamic mode decomposition (DMD) to simulate and analyze the coupling characteristics between self-excited sweeping jet and backward-facing step separated flow. The sweeping frequency of the fluidic oscillator is largely influenced by the external separated flow, thus changing its own frequency to the dominant frequency of the separated flow or its multiples. The flow loss is minor when the overall flow frequency is the dominant frequency of the separated flow or its multiples. Moreover, the fluidic oscillator velocity should not be too high to produce excessive unsteady disturbance to the freestream and increase the flow losses. When the inlet flow velocity is 65 m/s and the jet velocity of the fluidic oscillator is 40 m/s, the total pressure loss coefficient of the backward-facing step is reduced by approximately 4.7%. According to DMD analysis, the effective fluidic oscillator control can simplify the frequency mode and decrease its vortical motion loss. Combined with the streamwise amplification effect of the flow instability of the separated flow on the dominant DMD mode, the flow field is locked to some multiple of the dominant frequency of the uncontrolled flow field through the coupling effect of the fluidic oscillator and the separated flow.
GreenblattDWygnanskiIJ. The control of flow separation by periodic excitation. Prog Aero Sci2000; 36(7): 487–545.
2.
KhaboshanHNYousefiESvorcanJ. Analysis of the turbulent boundary layer and skin-friction drag reduction of a flat plate by using the micro-blowing technique. J Appl Mech Tech Phys2022; 63(3): 425–436.
3.
NiuJTWangJSLiuXL, et al.Micro-suction and micro-blowing on channel flow: large eddy simulation of velocity normalization, root-mean-square velocity fluctuations, and reynolds stress. Int J Green Energy2025; 22: 1947–1964.
4.
NishiokaMAsaiMYoshidaS. Control of flow separation by acoustic excitation. AIAA J1990; 28(11): 1909–1915.
5.
CaoSDangNRenZ, et al.Lagrangian analysis on routes to lift enhancement of airfoil by synthetic jet and their relationships with jet parameters. Aero Sci Technol2020; 104: 105947.
6.
GlezerAAmitayM. Synthetic jets. Annu Rev Fluid Mech2002; 34(1): 503–529.
7.
WilliamsNJMoellerTMThompsonRJ. Numerical simulations of high frequency transverse pulsed jet injection into a supersonic crossflow. Aero Sci Technol2020; 103: 105908.
8.
WangLFuS. Detached-eddy simulation of flow past a pitching NACA 0015 airfoil with pulsed actuation. Aero Sci Technol2017; 69: 123–135.
9.
ZhangHChenSMengQ, et al.Flow separation control using unsteady pulsed suction through endwall bleeding holes in a highly loaded compressor Cascade. Aero Sci Technol2018; 72: 455–464.
10.
SinhaS. Active flexible walls for efficient aerodynamic flow separation control. In: 17th applied aerodynamics conference. Reston: AIAA, 1999.
11.
WuCWangLWuJ. Suppression of the von Kármán vortex street behind a circular cylinder by a travelling wave generated by a flexible surface. J Fluid Mech2007; 574: 365–391.
12.
WeiBWuYLiangH, et al.Flow control on a high-lift wing with microsecond pulsed surface dielectric barrier discharge actuator. Aero Sci Technol2020; 96: 105584.
13.
WangZLiGChenB. Experimental investigation on characteristics of single-outlet fluidic oscillator. J Nanjing Univ Aeronaut Astronaut2015; 47(06): 877–883.
14.
JiangHLiaoR. Mechanistic research on self-excited oscillating impulse jet flow. J Southwest Pet Inst1998; 20(3): 55–58.
15.
LiuWKangYWangX, et al.Integrated CFD-Aided theoretical demonstration of cavitation modulation in self-sustained oscillating jets. Appl Math Model2020; 79: 521–543.
16.
SeoJHZhuCMittalR. Flow physics and frequency scaling of sweeping jet fluidic oscillators. AIAA J2018; 56(6): 2208–2219.
17.
AramSLeeYTShanH, et al.Computational fluid dynamic analysis of fluidic actuator for active flow control applications. AIAA J2018; 56(1): 111–120.
18.
ZhangYFuQMoC, et al.Molecular dynamics simulation of a nanoscale feedback-free fluidic oscillator. AIP Adv2017; 7(11): 115311.
19.
ZubairMWenX. Flow characteristics of a dual sweeping jet impinging on a flat surface. Actuators2025; 14(2): 101.
20.
JhaveriVDeSalvoMGlezerA, et al.Effects of manufacturing parameters on performance of fluidic oscillators for aerodynamic flow control. Proc Inst Mech Eng G J Aerosp Eng2018; 233(10): 3603–3611.
21.
WangSBaldasLColinS, et al. Experimental and numerical study of the frequency response of a fluidic oscillator for active flow control. 8th AIAA Flow Control Conference. Reston: AIAA, 2016.
22.
GregoryJWSullivanJPRaghuS. Visualization of jet mixing in a fluidic oscillator. J Vis2005; 8(2): 169–176.
23.
OstermannFWoszidloRNayeriCN, et al.Properties of a sweeping jet emitted from a fluidic oscillator. J Fluid Mech2018; 857: 216–238.
24.
TomacMNSundströmE. Adjustable frequency fluidic oscillator with supermode frequency. AIAA J2019; 57(8): 3349–3359.
CerretelliCKirtleyK. Boundary layer separation control with fluidic oscillators. J Turbomach2009; 131(4): 041001.
27.
CerretelliCWuerzWGharaibahE. Unsteady separation control on wind turbine blades using fluidic oscillators. AIAA J2010; 48(7): 1302–1311.
28.
KokluM. Effects of sweeping jet actuator parameters on flow separation control. AIAA J2018; 56(1): 100–110.
29.
ShmilovichAYadlinYWhalenEA. Active flow control computations: from a single actuator to a complete airplane. AIAA J2018; 56(12): 4730–4740.
30.
OstermannFGodbersenPWoszidloR, et al.Sweeping jet from a fluidic oscillator in crossflow. Phys Rev Fluids2017; 2(9): 090512.
31.
OstermannFWoszidloRNayeriCN, et al.The interaction between a spatially oscillating jet emitted by a fluidic oscillator and a cross-flow. J Fluid Mech2019; 863: 215–241.
32.
ChenSWLiWHXuCMQH, et al.Experimental study of corner separation and unsteady characteristics in linear compressor cascades with and without sweeping jet actuator. Propulsion and Power Research2024; 13(3): 360-374.
33.
YangPChenSLiuG, et al.Corner separation control using sweeping jet actuator in a compressor Cascade. J Turbomach2024; 146(10): 9.
34.
ShmilovichAKhodadoustACollettiCR, et al.Steady versus unsteady pneumatic flow control and aspects of practical integration. J Aircraft2024; 61(5): 1501-1516.
35.
ZhangHXChenSWGongY, et al.A comparison of different unsteady flow control techniques in a highly loaded compressor Cascade. P I Mech Eng G-J AER2019; 233(6): 2051-2065.
36.
ZhengFQLeeY. Unsteadiness of the control of shock-induced boundary-layer separated flow using supersonic fluidic oscillator. J Korean Soc Aeronaut Space Sci2023; 51(12): 841.
37.
KokluM. The effects of sweeping jet actuator parameters on flow separation control. In 45th AIAA fluid dynamics conference. Reston: AIAA, 2015.
38.
NiehuisRMackM. Active boundary layer control with fluidic oscillators on highly-loaded turbine airfoils. NNFM2015; 127: 3–22.
39.
SlupskiBJKaraK. Separated flow control over Naca0015 airfoil using sweeping jet actuator. In 35th AIAA applied aerodynamics conference. Reston: AIAA, 2017.
40.
LuWJiaoYFuX. Concept of self-excited unsteady flow control on a compressor blade and its preliminary proof by numerical simulation. Aero Sci Technol2022; 123: 107498.
41.
WygnanskiI.The variables affecting the control of separation by periodic excitation. 2nd AIAA Flow Control Conference, Reston: AIAA,2004.
42.
LiBYaoYChengK. Active control of 2D backward facing step separated flow based on synthetic jet. Acta Aeronautica Astronautica Sinica. 2016; 37(06): 1753–1762.
43.
MalekiMTalabazarFRKosarA, et al.On the spatio-temporal dynamics of cavitating turbulent shear flow over a microscale backward-facing step: a numerical study. Int J Multiphas Flow2024; 177: 104875.
44.
ShenXZengKYangL, et al.A new exploration on passive control of transonic flow over a backward-facing step. Int J Numer Methods Heat Fluid Flow2024; 34(7): 2601–2625.
45.
NicoudFDucrosF. Subgrid-scale stress modelling based on the square of the velocity gradient tensor. Flow Turbul Combust1999; 62(3): 183–200.
46.
NiccolòTLodatoGVervischL. A dynamical LES turbulence model applied to airfoil flows. AIAA Aviation 2020 Forum. Reston: AIAA, 2020.
47.
LysenkoDAErtesvagISRianKE. Large-eddy simulation of the flow over a circular cylinder at reynolds number 3900 using the openfoam toolbox. Flow Turbul Combust2012; 89(4): 491–518.
48.
WangGYTangYMWeiXD, et al.Predicting turbulent flow over a backward-facing step using grid-adaptive simulation method. Aero Sci Technol2025; 158: 109913.
49.
MinGJiangN. Data-driven identification and pressure fields prediction for parallel twin cylinders based on POD and DMD method. Phys Fluids2024; 36(2): 023614.
50.
AhaniHUddinM. Impact of key DMD parameters on modal analysis of high-reynolds-number flow around an idealized ground vehicle. Appl Sci (Basel)2025; 15(2): 713.
51.
CháVEZ-DoradoJScherlIDibenedettoM. Wave and turbulence separation using dynamic mode decomposition. J Atmos Ocean Technol2025; 42(5): 509–526.
52.
SchmidPJ. Dynamic mode decomposition of numerical and experimental data. J Fluid Mech2010; 656: 5–28.
53.
RowleyCWMezićIBagheriS, et al.Spectral analysis of nonlinear flows. J Fluid Mech2009; 641: 115–127.
