Scaling characteristics, essential to the mechanisms of transition in square-prism shear layers, were explored experimentally. In particular, the evolution of the dominant instability modes as a function of Reynolds number were reported in the range $1.5\times 10^{4}\lesssim Re_{D}\lesssim 7.5\times 10^{4}$. It was found that the ratio between the shear layer frequency and the shedding frequency obeys a power-law scaling relation. Adherence to the power-law relationship, which was derived from hot-wire measurements, has been supported by two additional and independent scaling considerations, namely, by particle image velocimetry measurements to observe the evolution of length and velocity scales in the shear layer during transition, and by comparison to direct numerical simulations to illuminate the properties of the front-face boundary layer. The nonlinear dependence of the shear layer instability frequency is sustained by the influence of $Re_{D}$ on the thickness of the laminar front-face boundary layer. In corroboration with the original scaling argument for the circular cylinder, the length scale of the shear layer was the only source of nonlinearity in the frequency ratio scaling, within the range of Reynolds numbers reported. The frequency ratio scaling may therefore be understood by the influence of $Re_{D}$ on the appropriate length scale of the shear layer. This length scale was observed to be the momentum thickness evaluated at a transition point, defined where the Kelvin–Helmholtz instability saturates.
Critical Conversations are held by members of the greater Engineering, Social Justice, and Peace network in the activist tradition of reflecting on our public engagement and collectively discovering ways of deepening our action. The particpants are selected based on their submissions (Expressions of Interest) in response to the Call for Participation in the Critcial Conversations disseminated through the ESJP website (esjp.org). For years, we have gathered in locations immersed in nature. In 2018 and 2019, the gathering took place in Cala Munda, organized by Caroline Baillie and Eric Feinblatt, in the beautiful Catskills mountains in upstate New York in the U.S.A. We want to feel our connection with the land while we engage in critical conversations on the intersection of the engineering field with social justice and peace. Caroline Baillie facilitates these conversations employing forest pedagogy. Through this pedagogy, we open our hearts to the forest for seeking guidance on how our profession can help restore, heal, and serve people, planet, and life instead of its current practice of destroying, pillaging, and harming nature. In the throes of the coronavirus pandemic, the urgency of action was evident in 2020 like never before. On June 26 and 27, 2020, a group of up to 40 educators, researchers, activists, and field practitioners, from 4 continents, met virtually for the 4th Annual Critical Conversations – almost thrice as large as the 2018 and 2019 groups that met in-person. The virtual format allowed for broader participation – both in numbers as well as geographical locations. Though we were physically separated in the online gathering, situated in our respective modern, often disconnected-from-nature enclaves, our hearts and minds were engaged in envisioning transition to a just and egalitarian society. In keeping with the need of the moment, our focus was on brainstorming action projects that we can implement in the near future. The retreat facilitated the formation of action teams, which spent the summer discussing possible action items moving forward. These teams are now looking for a more permanent structure with team leaders, team members, an infrastructure, and social media presence. This is a call to action! We carried out these deliberations in an open-space format, wherein the agenda for the two days was set by the participants. In the two sessions on day one, using this participatory approach, we were able to sift six main themes that participants were interested in exploring in-depth. On day two, we divided ourselves into six teams and each team took a deeper dive into their theme of choice. Five of these teams have written summaries of their deliberations and proposed their Calls to Action for the engineering community, which we report below.
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