Quieter air conditioning on aircraft
The subsonic air jet pump for the air conditioning system must be located in close proximity to the passenger and crew cabins. Since noise is linked to hearing impairment, cardiovascular dysfunction, sleep disturbance and decreased mental function, noise reduction here is particularly important. The EU-funded OPA (Optimisation of air jet pump design for acoustic application) project set out to evaluate designs for low noise. Project partners optimised a subsonic jet pump in terms of aerodynamics using Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) analyses. RANS identifies trends in flow behaviour when performing a parameter study, and LES provides reliable and accurate examination of the most promising configurations. They used RANS to select several configurations and performed numerical simulations through a turbulence model and commercial software. The OPA team analysed the production of turbulence kinetic energy, wall pressure distribution, uniformity index and the vorticity components. This helped to obtain information on the location and strength of the acoustic sources as well as on the mixing performance. It then selected the three most promising designs and the baseline for further experimentation and evaluation. The baseline configuration was manufactured and the three optimised solutions were designed. Researchers developed simulations of the unsteady regime of a simplified jet pump's operation. Findings were then compared to experimental data both to evaluate the performance of the test rig in producing accurate representations as well as to fine-tune the model for future development campaigns. The LES models were completed and applied to several configurations, revealing the most promising design. OPA shed light on subsonic jet pump aerodynamics, noise propagation and reduction techniques through a combined numerical and experimental approach. Successful noise reduction will have important benefits for passengers, crew and manufacturers alike.
Keywords
Air conditioning, subsonic air jet pump, noise reduction, OPA
