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

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 × 10 5 . Three streamwise x y x y $xy$ 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