TwinFlow simulates and visualizes airflow and temperature distribution in indoor environments such as houses, buildings, and data centers. The conventional and widely used Computational Fluid Dynamics (CFD) method requires extensive processing before simulation results become available. In contrast, TwinFlow delivers airflow and thermal simulation results instantly within a synchronized digital twin that combines a 3D environment model, IoT sensors, a proprietary simulation engine, and XR visualization. It serves both experts and general users. It lets engineers and facility operators optimize HVAC (Heating, Ventilation, and Air Conditioning) systems, evaluate cooling strategies, and improve energy efficiency through continuous operational decisions. It also helps general users find the best placement of air conditioners in offices and living rooms.