COMPUTATIONAL FLUID DYNAMICS COMES TO THE CONCERT HALL    PART 2

ORCHESTRAL MUSICIANS TEND to occupy the same seating at each concert performance. However, this may be changing to enhance circulation of air (and aerosols) suggested by studies of computational fluid dynamics.

Tidbits on this are gleaned from “Mitigation Strategies for Airborne Disease Transmission in Orchestras Using Computational Fluid Dynamics, by Hayden A. Hedworth et al, Science Advances, June 23, 2021; and “Musical Chairs? Swapping Seats Could Reduce Orchestra Aerosols, by Emily Anthes, The New York Times, June 23, 2021.

CFD in a New Setting. Applications of CFD have been familiar in aerospace, automotive, and even Olympic bobsleds. Added to these are studies of air circulation as it affects pandemic aerosols, such as those emitted by infected people upon exhaling. Particularly crucial, for example, are singers in close range to each other; thus, the hymnal controversy among church attendees. 

Orchestral CFD Studies. Also of concern are inherent exhalations of musicians through orchestral brass and woodwind. Indeed, it turns out that trumpets and oboes are particular culprits. 

Hayden Hedworth and his colleagues are in the Department of Chemical Engineering at University of Utah, Salt Lake City. They note that “a locally developed CFD code is used to simulate the airflow and spread of fine aerosols (<5 μm diameter) from multiple wind instruments in Abravanel Hall and Capitol Theater, two concert venues both located in Utah.”

“In addition,” they write, “quantitative microbial risk assessment is used to translate a reduction in aerosol concentration to a reduction in risk of infection. In each venue, we consider the stage area only and are interested in assessing the exposure and risk for the musicians on stage, not the audience.”

The Abravanel Hall Venue. Salt Lake City’s Abravanel Hall is home to the Utah Symphony, with a typical complement of 85 instrumentalists. The researchers identify the hall’s two main stage doors, left and right, each 8.2 ft. wide and 6.6 ft. high. For air circulation, there are five rows of supply vents that run along the ceiling and 14 return vents on the floor at the back of the stage.  

Based on these dimensions, flow patterns, and orchestral seating, the researchers used CFD to simulate air circulation throughout the orchestra section.

Trumpeters, Oboes as Culprits. The researchers’ simulations showed that the average aerosol concentrations “over much of the stage area approaches or exceeds 5 particles per liter. Large, high-concentration (>20 particles per liter) plumes are evident at the rear of the stage where the trumpets are located.”

Mitigation. The researchers note, “Mitigation strategies involved rearranging musicians and altering the airflow by changing HVAC settings, opening doors, and introducing flow-directing geometries.” 

In particular, the simulated trumpets were moved aft and stage right, close to the air return vents. Clarinets were relocated upstage, and oboes (also aerosol hotspots) were given stage left aft proximity to other air returns vents.

“Our results,” the researchers say, “indicate that the proposed mitigation strategies can reduce aerosol concentrations in the breathing zone by a factor of 100, corresponding to a similar decrease in the probability of infection.”

Emily Anthes, The New York Times, notes, “The Utah Symphony, for its part, proved open to rethinking the seating. And when it took the stage last fall, it did so with the stage doors open and the wind instruments at the rear. It took a few weeks for the musicians to get comfortable with the new arrangement, and they plan to return to their traditional seating configuration this fall….”

“But,” she said, “the simulations gave musicians an unusual solution, although their findings may have hit some instrumentalists harder than others.” 

For awhile, viola jokes thrived. (“What’s the latest NYC crime wave?” “Drive-by viola recitals.”) Maybe now it’s the trumpet’s turn. ds 

© Dennis Simanaitis, SimanaitisSays.com, 2021