Turbulence development under in-phase and anti-phase periodic inflows in a dual-fan wind tunnel with and without a turbulence grid

Fan-array wind tunnels provide highly controllable unsteady inflows; however, the interaction between phase-controlled adjacent fan outflows and grid-generated disturbances remains unclear. This study experimentally investigates turbulence development under in-phase and anti-phase periodic inflows in a dual-fan wind tunnel, with and without a classical square grid. A sinusoidal inflow is imposed using two adjacent fans operated in-phase or anti-phase, and streamwise and transverse velocity components are measured using an X-type hot-wire probe. A triple-decomposition procedure separates the imposed periodic motion from the nonperiodic fluctuation component by removing the spectral peak at the forcing frequency. Without the grid, in-phase operation preserves the imposed periodic fluctuation and produces limited turbulence development, whereas anti-phase operation generates a large time-dependent velocity difference between adjacent outflows, accompanied by higher harmonics and enhanced high-frequency spectral energy. With the grid installed, the anti-phase configuration exhibits the weakest forcing peak, a frequency interval with fitted slopes close to −5/3, and distinct high-frequency spectral steepening, indicating the strongest broadband spectral development among the present cases. It also shows the largest transverse fluctuation intensity and greatest downstream improvement in the two-component isotropy indicator. Triple-decomposition analysis further shows that the non-Gaussianity of the raw velocity statistics primarily originates from the imposed periodic component, while the extracted nonperiodic fluctuations exhibit near-zero skewness and flatness close to three. Overall, the anti-phase condition with the turbulence grid exhibits the strongest broadband spectral development and greatest improvement in the two-component isotropy indicator within the measured center-plane region.