Characteristics of shock-induced boundary layer separation on nacelles under windmilling diversion conditions

The boundary layer on the external cowl of an aero-engine nacelle under windmilling diversion conditions is subjected to a notable adverse pressure gradient due to the interaction with a near-normal shock wave. Within the context of Computational Fluid Dynamics (CFD) methods, the correct representation of the characteristics of the boundary layer is a major challenge to capture the onset of the separation. This is important for the aerodynamic design of the nacelle as it may assist in the characterization of candidate designs. This work uses experimental data obtained from a quasi-2D rig configuration to provide an assessment of the CFD methods typically used within an industrial context. A range of operating conditions is investigated to assess the sensitivity of the boundary layer to changes in inlet Mach number and mass flow through a notional windmilling engine. Fully turbulent and transitional boundary layer computations are used to determine the characteristics of the boundary layer and the interaction with the shock on the nacelle cowl. The correlation between the onset of shock induced boundary layer separation and pre-shock Mach number is assessed and the boundary layer integral characteristics ahead of the shock and the post-shock recovery evaluated and quantified. Overall, it was found that the CFD is able to discern the onset of boundary layer separation for a nacelle under windmilling conditions

From an experimental paper to a playful screen : How the essence of materiality modulates the process of creation

The article seeks to develop a better understanding of the contribution of materiality in a discourse between a creator (content producer) and an interface, dealing with analogue and digital artefacts. Focus is in the materiality of the two different art-creation learning processes, acrylic painting and digital painting. The objective of this paper is to consider especially the affect and meaning of these two different content creation modalities and intra-action within that. Through reflective autoethnographic consideration, the purpose is to consider the essences of materials manifesting and modulating the processes of content creation as a posthumanist phenomenon. It will be shown that the creation processes with paper are more experimental whereas the processes with digital screen are more playful. There is a growing need to deeper understand the cultural change of material cultures and the people's intra-action with the materials also enabling arts creation. This paper will widen our limited understanding and deepen our theoretical perspectives of the essence of materials which then avails confronting analogue and digital when developing teaching and learning in the posthuman era especially in early education. Practitioner Notes What is already known about this topic There is a growing interest in the new materialism and posthuman thinking amongst educational technology research and development. Reading analogue versus digital is well-documented. What this paper adds New materialist thinking offers a useful perspective in education for looking at the essence of analogue and digital materiality modulating content creation. Characterising the nuances in analogue and digital production can help in evaluating their educational potential. Implications for practice and/or policy As practitioners we should critically question the political vision of education digitalisation especially concerning early childhood education. There is a need to move beyond debates about analogue versus digital to look at more specific examples of their advantages (and disadvantages) in developing posthumanist education and intra-active pedagogy especially for young children.Peer reviewe

Numerical and experimental investigations of diffusion-induced boundary layer separation on aero-engine nacelles

Aero-engine nacelles have to fulfill design requirements at both cruise and off-design conditions. Under engine windmilling conditions the ingested streamtube massflow is relatively low. A key off-design condition is take-off, which, in conjunction with an engine windmilling scenario, results in the stagnation point of the ingested streamtube being located significantly inside the intake. The combination of high angle of attack and low engine massflow rates leads to a strong flow acceleration and subsequent diffusion of the boundary layer on the upper quadrants of the external nacelle cowl, which can terminate with subsonic separation from the leading-edge. Under this condition, Reynolds number effects can play a dominant role on the separation onset and characteristics and 3D-annular wind tunnel tests cannot always achieve Reynolds’ number equivalent to full scale. A novel quasi-2D rig configuration representative of the aerodynamics of a full-size aero-engine nacelle under windmilling end of runway conditions examined in detail the characteristics of the boundary layer on the external cowl of a nacelle prior to diffusion-induced separation. Separation of the boundary layer was independently promoted through changes to represent different engine massflow rates and freestream Mach number on the rig to determine the limits of steady Reynolds Averaged Navier Stokes (RANS) methods to discern the onset of boundary layer separation. For the conditions and geometry investigated, the combined experimental and computational results showed that there was laminar to turbulent transition of the boundary layer ahead of the subsonic diffusion. The work showed that steady RANS can predict the onset of boundary layer separation with an uncertainty of approximately 10% on notional engine massflow rate and 0.05 on freestream Mach number relative to a nominal operating freestream Mach number of 0.25. This provides guidance for the industrial design and optimization of future windmilling-tolerant nacelles for large ultra-high bypass ratio turbofan engines