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One of our and our clients’, key objectives is the reduction of flow aero-noise produced in HVAC components and to increase the airflow rate of the air-conditioning at lower fan input powers.
The test case investigated by OYL research department was a cross flow fan. This problem involves complex geometries and flow physics; requiring meshing of a 2-D geometry, running a transient setup with moving mesh motion.
Using FLUENT, the CFD simulation is studied to examine the effects of parameters such as scroll design, blade angle, blade shape and heat exchangers layout on flow pattern inside the wall mounted air-conditioner.
We generated approximately 60,000 quadrilateral cells in total with coarser mesh defined at the upstream and downstream of computational domain.
The modeling strategy employs RNG k-ε turbulence model with enhanced wall treatment for solving the turbulence sources. The initial study conducted at steady state with multiple reference frames (MRF) approach, followed by the transient solver and sliding mesh (SM) approach.
The rotation speed for the cross flow fan (CFF) ranged from 1100 to 1250rpm. For the MRF, a steady-state solution is first obtained. It is then validated for the unsteady sliding mesh calculation. Porous media approach was used to predict the pressure drop across the heat exchangers. In order to obtain the pressure drop coefficients, the flow rate and pressure drop across the heat exchanger was carried out by experimental work using in-house test jig.
The CFD results were compared with the experimental data and good agreement was achieved. The velocity vector plot shows that eccentric vortex occur within the blades region. The results are fundamental for improving the design rules with less actual trial-out.
References
[1] Bleier, F. P., Fan Handbook: Selection, application and design, McGraw-Hill, United States Of America, 1998.
[2] Sakai H., Tokushige S., Ishikawa M., and Ishihara T., Numerical analysis for the air flow of cross flow fan, Trans. of JSRAE, Vol.17, No.2 (2000), pp.137-146.
[3] Klemm T. and Gabi M., Using PIV to investigate the effect of casing design on cross flow fan performance, Proceedings of PSFVIP-4,Chamonix, France, June 3-5, 2003.
Velocity vectors showing eccentric vortex within the blades region.
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