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Fresh Air for the Coliseum PUBLIC ACCESS

A London Engineering Firm Helps an Audience Breathe Easier.

[+] Author Notes

This article was prepared by staff writers in collaboration with outside contributors.

Mechanical Engineering 123(07), 64-65 (Jul 01, 2001) (1 page) doi:10.1115/1.2001-JUL-4

The London Coliseum management has handed Arup, a London-based engineering firm, to improve support facilities, to provide better access to the building, and to enhance its general appeal, which includes improving theatre goers' comfort through the quality of ventilation. In order to learn exactly what to expect of its proposed ventilation system for the London Coliseum, Arup created a model composed of more than a half-million cells. Minor adjustments have already been made to improve the existing system. Arup plans a modern design in which air is supplied through nozzle banks in the domed ceiling. This will create a swirling airflow within the auditorium that won't affect the quality of the acoustics. Air is extracted at the back of three seating regions. Arup’s computational fluid dynamics study took approximately 5 weeks to complete on a DEC Alpha Unix workstation.

The London Coliseum, home to the English National Opera, is pushing 100 and, as it nears its second century, the venue is engineering a makeover.

The Coliseum's management has handed Arup, a London-based engineering firm, a to-do list-to improve support facilities, to provide better access to the building, and to enhance its general appeal, which includes improving theatergoers' comfort through the quality of ventilation.

The volume of the London Coliseum's auditorium is immense, almost 15 ,000 cubic meters, or a half-million cubic feet. After all, the building's namesake is the place where the Romans used to hold mock sea battles and other spectacles. So it should come as no surprise that improving air circulation represents a major part of Arup's work.

Minor adjustments have already been made to improve the existing system. In preparation for an entirely new ventilation system, to be installed during the English National Opera's off-season over the next three years, Arup studied the airflow of the auditorium using computational fluid dynamics.

The London Coliseum was completed in late 1904 and, since then, has enjoyed a diverse role in show business. Its offerings have ranged from horse races to variety shows and movies.

The Coliseum started with a plenum-style ventilation system that was changed in 1932 to a design that supplied air at the floor and extracted it at the ceiling. The current air handling units and horizontal ductwork were installed 50 years later, in 1982.

Arup plans a new design in which air is supplied through nozzle banks in the domed ceiling. This will create a swirling airflow within the auditorium that won't affect the quality of the acoustics. Air is extracted at the back of three seating regions.

The computational domain for Arup's ventilation study contained approximately 550,000 cells and represented the main auditorium.

The problem was to see how best to optimize the nozzle system in the domed ceiling by tweaking the mechanical air extraction system. Air is exhausted through grilles positioned at the rear of the balcony, upper circle, and dress circle. The model included those areas, the stalls (corresponding to orchestra seats in the United States), the orchestra pit, and three of the theater's many boxes.

For its CFD calculations, Arup used STAR-CD from Computational Dynamics Ltd. in London. Engineers loaded the results into EnSight, visualization software from CEI of Apex, N.C., and were able to see airflow patterns as animated particle trace paths. Predicted air velocities were plotted on bounding surfaces for the audience-occupied zones and along a streamline for particle traces.

"The air movement is very complex," said Darren Woolf, a fluid dynamicist at Arup. "It's driven by jet momentum, air temperature differentials, and wall-to-air temperature differentials that vary spatially and in magnitude. We needed to understand all of these factors and their various influences in order to improve the design of the system."

Arup ran three case scenarios. In all three, air introduced through the nozzles was set at 17°C, or 63°F. The model included a convective heat load equivalent to 35W per person for the total 2,364-person occupancy, in order to understand the atmosphere of the Coliseum under peak conditions. Lighting and other stage effects were not taken into consideration, as a neutral boundary was assumed between the stage and audience areas.

In order to learn exactly what to expect of its proposed ventilation system for the London Coliseum, Arup created a model composed of more than a half-million cells.

Grahic Jump LocationIn order to learn exactly what to expect of its proposed ventilation system for the London Coliseum, Arup created a model composed of more than a half-million cells.

A visualization of air temperature distribution in the best-case scenario: 40 percent of the airflow is extracted at the rear of the dress circle.

Grahic Jump LocationA visualization of air temperature distribution in the best-case scenario: 40 percent of the airflow is extracted at the rear of the dress circle.

The computer pictures currents in the auditorium space; air enters from nozzles in the ceiling dome and circulates before it is extracted at the rear of the dress circle, upper circle, and balcony.

Grahic Jump LocationThe computer pictures currents in the auditorium space; air enters from nozzles in the ceiling dome and circulates before it is extracted at the rear of the dress circle, upper circle, and balcony.

In the first case, air was extracted in equal volumes: 33.3 percent from each of the three vented sections. CFD testing revealed that airflow in the balcony area was short-circuited; that is, air was extracted before it had a chance to effectively cool the occupants. Likewise, a fresh supply of air was unable to penetrate far enough into the lower regions, such as the expensive stalls seating, resulting in stagnant airflow and higher temperatures.

In a second trial, engineers varied the amount of air being drawn from each section: 50 percent of the air volume drawn out through the dress circle (governing the most-populated sections), 30 percent through the upper circle, and 20 percent through the balcony. Analysis showed that the new percentages increased the scope of the swirling airflow, allowing it to reach occupants in the dress circle and the stalls.

The changes were an overcompensation, but temperatures were spread more evenly throughout the audience than in the first instance.

A third case assigned 40 percent of air circulation to the dress circle, 33 percent to the upper circle, and 27 percent to the balcony. Engineers saw that the swirling air penetrated lower in the sea ting areas, resulting in cooler temperatures in the most densely populated sections. This scenario was determined to be the optimum choice for the ventilation system.

Arup's CFD study took approximately five weeks to complete on a DEC Alpha Unix workstation.

Thanks to the engineers, opera enthusiasts can enjoy their favorite arias in comfort, as the anguish takes place on the stage, not in the seats.

Copyright © 2001 by ASME
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