Real-time numerical simulations of data center air-cooling is achieved using a computational fluid dynamics research code executed on multiple graphics processing units (GPUs). The simulated thermal fields are validated against transient time-series data recorded during the experimental operation of a slab-floor data center that is thermally managed using computer room air handling units.A developed lattice Boltzmann method (LBM) simulation using the Bhatnagar-Gross-Krook (BGK) collision operator is employed to model both the momentum and energy transport equations of fluid dynamics. Airflow turbulence is captured using a large eddy simulation (LES) approach and the effects of natural convection of the air are included using the Boussinesq approximation.The BGK-LBM computation is distributed across 10 GPUs on a multi-GPU remote server. Using optimization strategies for synchronization between GPUs, the computational performance is shown to scale almost linearly with the number of GPUs involved. A parallel algorithm based on MapReduce is developed that can provide continuous measurements of the simulated macroscopic field variables. Agreement between the simulated and measured fields is shown. The numerical simulation can be executed in real-time or faster depending on the lattice resolution.