Multi-plane turbulence structures and instantaneous velocity extremes in high-Reynolds-number deep cavity flow

Abstract

Abstract Content of image described in text. Systematic experimental data on local extreme velocities and unsteady features in high-Reynolds-number deep-cavity flows remain limited. In this study, two-component particle image velocimetry (PIV) measurements were performed to investigate the flow characteristics of an incoming-flow-driven deep cavity with upper L divided by upper D L/D $L/D$ = 1 divided by 3 1/3 $1/3$ at Re = 2.55 × 105. Three streamwise x y xy $xy$ planes ( z divided by upper W z/W $z/W$ = 0.10, 0.25, 0.50) and three spanwise yz planes ( x divided by upper L x/L $x/L$ = 0.10, 0.25, 0.50) were measured systematically. The time-averaged velocity, root mean square velocity fluctuations, in-plane turbulent kinetic energy (TKE), instantaneous maximum velocity, and higher-order statistics including skewness and kurtosis were analysed. The results show that the vertical velocity fluctuation on the intermediate streamwise plane ( z divided by upper W z/W $z/W$ = 0.25) reaches peak value approximately v v $v$ rms /U lid = 0.072 (where U lid is the characteristic inflow velocity above the cavity), indicating the strongest local vertical unsteady response among the measured streamwise planes. On the near-wall plane ( z divided by upper W z/W $z/W$ = 0.10), the instantaneous maximum velocity exhibits skewness 1.23 and kurtosis 7.47, reflecting pronounced local intermittent extreme events, whereas the extreme events on the middle plane ( z divided by upper W z/W $z/W$ = 0.50) are weaker and closer to a Gaussian-like distribution. The spanwise planes also demonstrate clear non-Gaussian features, with high-fluctuation and high in-plane TKE regions primarily concentrated in areas associated with the interaction between the shear layer and recirculation structures, revealing significant spatial anisotropy in the flow. These results suggest that shear-layer development, primary recirculation, sidewall confinement and downstream flow turning jointly modulate local extreme events and intermittent velocity fluctuations. This study provides systematic experimental quantification of spatial non-uniformity and extreme-event characteristics in a high-Reynolds-number deep cavity using multi-plane PIV, offering useful experimental references for turbulence model validation and complex cavity-flow control.