Role of polymeric coating on metallic foams to control the aeroacoustic noise reduction of airfoils with permeable trailing edges

Hedayati, R.; Rubio Carpio, A.; Luesutthiviboon, S.; Ragni, D.; Avallone, F.; Casalino, D.; van der Zwaag, S.

doi:10.3390/ma12071087

Role of polymeric coating on metallic foams to control the aeroacoustic noise reduction of airfoils with permeable trailing edges

Title

Role of polymeric coating on metallic foams to control the aeroacoustic noise reduction of airfoils with permeable trailing edges

Author

Hedayati, R. (TU Delft Novel Aerospace Materials)
Rubio Carpio, A. (TU Delft Aircraft Noise and Climate Effects)
Luesutthiviboon, S. (TU Delft Aircraft Noise and Climate Effects)
Ragni, D. (TU Delft Wind Energy)
Avallone, F. (TU Delft Flow Physics and Technology; TU Delft Wind Energy)
Casalino, D. (TU Delft Flow Physics and Technology; TU Delft Wind Energy)
van der Zwaag, S. (TU Delft Novel Aerospace Materials)

Department

Flow Physics and Technology

Date

2019

Abstract

Studies on porous trailing edges, manufactured with open-cell Ni-Cr-Al foams with sub-millimeter pore sizes, have shown encouraging results for the mitigation of turbulent boundary-layer trailing-edge noise. However, the achieved noise mitigation is typically dependent upon the pore geometry, which is fixed after manufacturing. In this study, a step to control the aeroacoustics effect of such porous trailing edges is taken, by applying a polymeric coating onto the internal foam structure. Using this method, the internal topology of the foam is maintained, but its permeability is significantly affected. This study opens a new possibility of aeroacoustic control, since the polymeric coatings are temperature responsive, and their thickness can be controlled inside the foam. Porous metallic foams with pore sizes of 580, 800, and 1200 μm are (internally) spray-coated with an elastomeric coating. The uncoated and coated foams are characterized in terms of reduced porosity, average coating thickness and air-flow resistance. Subsequently, the coated and uncoated foams are employed to construct tapered inserts installed at the trailing edge of an NACA 0018 airfoil. The noise mitigation performances of the coated metal foams are compared to those of uncoated metal foams with either similar pore size or permeability value, and both are compared to the solid trailing edge reference case. Results show that that the permeability of the foam can be easily altered by the application of an internal coating on the metallic foams. The noise reduction characteristics of the coated foams are similar to equivalent ones with metallic materials, provided that the coating material is rigid enough not to plastically deform under flow conditions.

Subject

Aero-acoustics
Metal foam
Noise reduction
Noise-control
Spray coating
Trailing edge
noise-control
aero-acoustics
metal foam
noise reduction
spray coating
trailing edge