Air Flow Model Of The Bellarussian National Academic Grand Theatre Of Opera And Ballet

The National Academic Grand Theatre of Opera and Ballet or Opernyi teatr (in Russian), was built between 1935 and 1937 by Josef Langbard and opened with a performance of Eugene Tikotsky's Michas Padhorny. Since then the theatre has endured closure due to invasion during World War 2, the fall of communism and independence from Russia. In 2006 the renovation of the theatre began with an overhaul of the interior decoration and all the stage equipment.

As part of the renovation the complete installation of a new lighting system, significantly more powerful than the existing installation, was undertaken. This new system posed significant engineering challenges as the heat generation increased significantly leading to the need to retrofit a new air conditioning and cooling system. This new system was designed to not only ensure that the lighting itself does not overheat but also that occupant comfort in the auditorium was not adversely affected.

The theatre itself, in fitting with its grand nature, encloses a massive volume of air, with a stage suitable for up to 60 actors, an orchestra pit housing 83 musicians and over 1000 seats in the auditorium. The seating area can be subdivided into three areas, the stalls, balcony and dress circle. The stalls and stage are cooled by a displacement ventilation system while the orchestra pit and balcony use convection top-to-top ventilation.  In the stalls air is supplied through special low-speed distributors located under the seats of the audience.

To ensure that the ventilation installed is effective enough to ensure that both audience, orchestra, actors and lighting stay comfortable; simulations were carried out using STAR-CD. A “worst case scenario” study was carried out looking at the conditions that are likely to be encountered during a performance, with a full auditorium, orchestra and stage up to capacity with performers, stage lights on and house lights off.

A fully unstructured mesh was used to simulate the temperature and flow within the theatre with inlets used to simulate the ventilation systems and volumetric heat sources for the audience, actors, lights etc. Inlet volumetric flow rates and temperatures are shown in table 1. Given the anisotropic and largely buoyancy driven nature of the flow, the quadratic k-ε model was used.  

Table 1 Inlet boundary conditions for the theatre ventilation results

It is seen that the temperature distributions throughout the height of the theatre are considerably non-uniform primarily due to the displacement ventilation scheme as well as the considerable height of the building itself, the leads to a dominance of buoyancy-convective flows of warm air in a large part of the volume.

It is seen that the large amounts of heat generated by the lights (generating up to 900 kW of power) actually lead to overheating of the stage area. This in turn leads to air “spilling” into the main auditorium and out through the ceiling exhaust ventilation.  The positioning of the lights is non uniform so the volume above the stage, some 27 meters high, high temperature gradients are formed with a considerable velocity, due to buoyancy effects, present. That said the temperature on stage does remain within comfortable values.

It is also seen that in the balcony zone convection currents produced by the heating of the air by the occupants deflects the inlet cool air stream so increasing the mean age of air and reducing the comfort of the occupants. The stalls are effectively cooled with temperatures in the expected range, it seems that the cheap seats certainly live up to their name!

To better analyse the effect of the under seat ventilation, studies were carried out on an individual audience member sitting in their seat. Again inlet boundary conditions are used to model the effect of the inlet ducts and the resulting temperature field studied to evaluate the ventilation scheme’s effectiveness.

It can be seen that the given the flow rates the occupant of the seat remains at a comfortable temperature of between 22 and 24 ˚C with air velocities below 0.2m/s. This would conform well to the occupant comfort requirements with moderate temperatures and velocities low enough not to irritate the occupant.

Conclusion

The integration of CFD into the design stage of the renovation process allowed the simulation of flow fields around an extremely large volume that would otherwise be impractical, indeed physical testing of such a situation would be near impossible. Lack of numerical and/or experimental results in such an expensive and extensive re-fit could lead to damage of electrical equipment and un-sellable seats this in turn would facilitate a costly and disruptive retrofit of ventilation within the theatre. This study quickly showed potential floors in the design, specifically the lack of effectiveness of the ventilation around the balcony area, this in turn lead to a redesign to compensate so ensuring that all occupants remain comfortable throughout the performance.