Leading Edge Bumps for Flow Control in Air-Cooled Condensers

Abstract

Air-cooled condensers (ACCs) are commonly found in power plants working with concentrated solar power or in steam power plants operated in regions with limited water availability. In ACCs, the flow of air is driven toward the heat exchangers by axial fans that are characterized by large diameters and operate at very high mass flow rates with a near-zero static pressure rise. Given the overall requirements in steam plants, these fans are subjected to inflow distortions, unstable operations, and are characterized by high noise emissions. Previous studies show that leading edge bumps in the tip region of axial fans can effectively reduce the sound pressure levels without affecting the static efficiency. Nevertheless, the effects of this treatment in terms of flow patterns and heat exchange in the whole ACC system were not investigated. In this work, the effect of leading edge bumps on the flow patterns is analyzed. Two RANS simulations were carried out using OpenFOAM on a simplified model of the air-cooled condenser. The fans are simulated using a frozen rotor approach. Turbulence modeling relies on the RNG k-epsilon model. The fan is characterized by a diameter of 7.3 m and a 333 m3/s volumetric flow rate at the design point. The presence of the heat exchanger is modeled using a porous medium. The comparison between the flow fields clearly exerts that the modified blade is responsible for the redistribution of radial velocities in the rotor region. This drastically reduces the losses related to the installation of the fan in a real configuration.

Design of Sinusoidal Leading Edge for Low-Speed Axial Fans Operating under Inflow Distortion

“…The design and optimization process of the baseline geometry is fully described in [40]. The fan has previously been extensively investigated using actuator line models [41,42] and fully resolved CFD [43][44][45]. The design of the sinusoidal LE is based on the concept of controlling the interaction between the separation on the suction side of the blade and the tip leakage vortex.…”

“…The computational grids were generated using the OpenFOAM-v22.06 snappyHexMesh built-in utility, using a background grid of 0.2 m isotropic cells. Grid refinement is based on the grid sensitivity analysis reported in [47]. Both grids (modified and baseline rotors) entail approximately 18M cells.…”