Barr’s computational fluid dynamics (CFD) specialists helped the City of Minneapolis solve the problem of stormwater “geysers” erupting on a road during especially intense rainfalls. The jets of water and air, which would shoot up through 16-inch-diameter drains connected to a stormwater tunnel about 100 feet below ground, were forceful enough to dislodge metal drain covers, and posed a safety risk to nearby pedestrians and vehicles.
By developing a CFD model to simulate turbulent flows and pressure fluctuations in mixtures of air and water, our CFD specialists were able to simulate the tunnel system’s hydraulics and evaluate two causes of geysers: surges in water pressure (known as transient flows) and the presence of large pockets of air that can become entrained, or trapped, in the water and lead to explosive releases at the surface.
To calibrate the CFD model, Barr used pressure measurements taken in the tunnel during storm events, as well as maintenance records of drain-hole covers being displaced. We then ran numerous model simulations to test various methods of preventing stormwater geysers, included enlarging the drill holes, relocating them, and installing surge chambers below the road to accommodate excess stormwater.
The simulations indicated that the most effective solution would be to install surge chambers. Barr used the model results to develop hydraulic design criteria for the surge chambers, which would contain stormwater while allowing air to escape.
No geysers or dislodged covers have been observed since construction of the chambers in 2019, which ultimately translates into improved safety for vehicles on the road and pedestrians close to it.