Evolution characteristics of 3D vortex structures in stratified swirling flames studied by dual-plane stereoscopic PIV

Extensional study of optical-flow enhanced hybrid PIV method for dual-plane stereoscopic PIV measurement

“…As a continuation of our previous works [5,13], the present work serves as an extensional study of the hybrid PIV method proposed in [27] for the DP-s-PIV measurement to enhance the spatial resolvability of tiny vortices. Briefly, the extension scheme presented in section 3 first generates the refined 2D2C velocity field for each camera through the hybrid PIV method, then reconstructs the refined 2D3C velocity field for each camera group using backprojection-based 3C velocity reconstruction, and finally obtains the refined 3D3C velocity and vorticity field via data interpolation.…”

“…where θ is the vane angle, D hub and D sw are the hub diameter and the outer diameter of the swirler, respectively. In the studied case, the mean exit velocities Ūexit at the outlets of the pilot and main stages are 6.6 and 12.8 m s −1 , yielding the resultant Reynolds numbers Re = Ūexit L v of 4425 and 6900, respectively [5]. The hydraulic diameter L of the outlets of the pilot and main stages are 10.5 and 8.5 mm, respectively, and v is the kinematic viscosity of the room-temperature air.…”

“…A high-speed DP-s-PIV was performed for the non-reacting swirling flow in the unconfined Beihang Axial Swirler Independently Stratified (BASIS) burner [5] under atmospheric pressure. As shown in figure 1(a), this burner consists of two concentric annular nozzles, namely, the central pilot stage (marked by a red arrow) and an outer main stage (marked by a blue arrow).…”

“…The room-temperature air streams in the two stages were regulated by two mass flow controllers (Sevenstar, CS200A), and the total air flow rate was kept constant ( ṁAir = 6 g s −1 ) with an air split ratio (ASR) of about 1:8. Note that the ASR is the ratio of the mass flow rate of the air stream in the pilot stage to that of the air stream in the main stage [5,30]. A double-swirling flow is then formed as the two air streams pass through the inner swirler (S ≈ 0.7, 8 vanes) and the outer swirler (S ≈ 0.5, 20 vanes), respectively.…”

“…Based on the hydraulic diameter L and resultant Reynolds numbers, the evaluated Taylor microscale λ = √ 10LRe − 1 2 [4] ranges from about 0.3 − 0.5 mm in the studied case. Alumina particles (diameter ∼1 µm) were used for flow seeding, which have [32] of about 3.2 × 10 −6 s with a corresponding Stokes number Stk = τ Umax DH [5,32] of about 7.1 × 10 −3 , suggesting reliable flow tracing accuracy [14]. Furthermore, as shown in figure 1(a), the selected non-reacting flow case can yield a uniform particle flow without apparent density stratification, which is beneficial for the accuracy of optical-flow evaluation.…”