Pressure shielding mechanism of canopies for trailing edge noise reduction in aerofoils

Session: Airframe / High-Lift Noise IView Video Presentation: https://doi.org/10.2514/6.2023-3204.vidThe pressure shielding mechanism of bio-inspired surface treatment, called canopies, has been investigated experimentally and applied to reduce trailing edge noise generated by aero- foils. Surface pressure experiments beneath the boundary layer on a flat and aerofoil section show that canopies can attenuate surface pressure in two frequency ranges, ∆ f 1 = 0.1 to 1.0 kHz and ∆f2 = 2 to 12 kHz, at some critical canopies’ height from the wall. Canopies with an Open-Area-Ratio (OAR or σ) of 50 % placed closer (h/δ=0.08) to the surface tend to in- crease attenuation with frequency, without any low-frequency peak attenuation. This high- frequency attenuation is mainly due to the mechanism of dissipation, of small-scale structures in the boundary-layer, provided by the canopies, which have relatively higher wall shear stress compared to flat plate or thicker canopy designs. As h/δ increases, the low-frequency atten- uation in the surface pressure becomes noticeable, with a peak value of 5 dB for a critical height of h/δ∗ ∼ 1, indicating the mechanism of blockage or shielding of large structures in the boundary-layer is responsible for the low-frequency attenuation. For h/δ ≥ 0.16, both the low- and high-frequency attenuation reduces and becomes almost zero for h/δ = 0.5. Furthermore, the mechanism of pressure shielding provided by the canopy treatment is shown to be a local phenomenon, for 70% <OAR < 90 % and very sensitive to the location of the canopy itself. The maximum attenuation in surface pressure is seen for the canopy geometries with small rod diameters with less spacing. The optimum canopy geometry, based on the surface pres- sure studies, was applied near the trailing edge of the NACA0012 aerofoil. The far-field noise study demonstrates, for the first time, that canopies can reduce broadband noise levels up to 12-14 dB in the frequency range between 2 and 12 kHz, provided they are scaled appropriately based on the incoming turbulent boundary-layer flow.EPSRC under grant No. EP/V038273/1

Modified TNO-Blake model for aerofoil surface pressure prediction with canopies

Session: Airframe / High-Lift Noise IView Video Presentation: https://doi.org/10.2514/6.2023-3203.vidThe modelling of the surface pressure spectrum beneath a turbulent boundary layer near the trailing edge of an aerofoil with bio-inspired surface treatments, called canopies, is investigated. Canopies are simply a cylindrical rods uniformly spaced along the span of the aerofoil. The velocity measurements indicated that the flow at the trailing edge of an aerofoil treated with canopies is localised and shows periodic behaviour across the span with treatment spacing. As a result, the mean-flow velocity gradient along the span (@U1=@x3) cannot be assumed as zero for x2=h = 4, which is shown in this paper. Therefore, the original surface pressure solution of Poisson’s equation is modified by introducing an additional source term consisting of the mean-shear contribution, given as @U1=@x3 @u3=@x1. Furthermore, the surface pressure attenuation due to the canopies shows a periodic behaviour across the span for treatments with an Open-Area-Ratio (OAR) between 70% and 90 %. This observation is consistent with our previous experimental results; therefore, the primary motivation for proposing a 3D TNO-Blake model, accounting for the interaction between the gradient of the stream-wise mean velocity along the span and span-wise fluctuating component along the stream. The model is built based on the inputs from Large Eddy Simulation results and additional wind tunnel measurements.EPSRC under grant No EP/V038273/1

M&A and diversification strategies: what effect on quality of inventive activity?

The aim of this paper is to examine how an acquirer's diversification strategy shapes the multiple dimensions of inventive activity. Differing from prior research, we use a set of indicators to investigate this phenomenon. In particular, we consider three different but complementary dimensions of inventive quality: technological impact, originality of the synthesized knowledge streams, and generality of applicability across different technological domains. The results obtained using a quasi-experimental approach show that diversification via acquisitions has a negative effect on post-acquisition technological impact. However, firms that have diversified outperform those firms that have not. Last, the acquirer's originality and generality increase after the merger and acquisition transaction, evidencing that the inventive activity benefited from the diversification strategy