skip to main content

Search for: All records

Creators/Authors contains: "Ahmed, K."

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Abstract

    Bio-inspired flow control strategies can provide a new paradigm of efficiency and adaptability to overcome the operational limitations of traditional flow control. This is particularly useful to small-scale uncrewed aerial vehicles since their mission requirements are rapidly expanding, but they are still limited in terms of agility and adaptability when compared to their biological counterparts, birds. One of the flow control strategies that birds implement is the deployment of covert feathers. In this study, we investigate the performance characteristics and flow physics of torsionally hinged covert-inspired flaps mounted on the suction side of a NACA2414 airfoil across different Reynolds numbers, specifically 200,000 and 1,000. These two Reynolds numbers are representative of different avian flight regimes where covert feathers have been observed to deploy during flight, namely cruising and landing/perching. We performed experiments and simulations where we varied the flap location, the hinge stiffness, and the moment of inertia of the flap to investigate the aerodynamic performance and describe the effects of the structural parameters of the flap on the aerodynamic lift improvements. Results of the study show up to 12% lift improvement post-stall for the flapped cases when compared to the flap-less baseline. The post-stall lift improvement is sensitive to the flap’s structural properties and location. For instance, the hinge stiffness controls the mean deflection angle of the flap, which governs the resulting time-averaged lift improvements. The flap moment of inertia, on the other hand, controls the flap dynamics, which in turn controls the flap’s lift-enhancing mechanism and how the flap affects the instantaneous lift. By examining the time-averaged and instantaneous lift measurement, we uncover the mechanisms by which the covert-inspired flap improves lift and highlights similarities and differences across Reynolds numbers. This article highlights the feasibility of using covert-inspired flaps as flow control across different flight missions and speeds.

    more » « less
  2. Abstract

    Flow control is the attempt to favorably modify a flow field’s characteristics compared to how the flow would have developed naturally along the surface. Natural flyers and swimmers exploit flow control to maintain maneuverability and efficiency under different flight and environmental conditions. Here, we review flow control strategies in birds, insects, and aquatic animals, as well as the engineered systems inspired by them. We focus mainly on passive and local flow control devices which have utility for application in small uncrewed aerial and aquatic vehicles (sUAVs) with benefits such as simplicity and reduced power consumption. We also identify research gaps related to the physics of the biological flow control and opportunities for device development and implementation on engineered vehicles.

    more » « less
  3. In this case study, we found three primary factors that influenced the high rates of teacher retention in the Kingfisher School District. The first was that teaching was seen as both a good and available job for which the Kingfisher teachers were well-qualified. Second, having a career in their home community appeared to be important many teachers and administrators in Kingfisher. This was strongly related to teachers’ identification and sense of belonging with the local Native American tribe. There was ample evidence that teachers saw their work in schools as an extension of kinship and community ties, and that schooling in Kingfisher was not antithetical to sustaining indigenous culture, as might be the case in other public-school districts with significant indigenous populations. Finally, teachers uniformly noted that that they were provided opportunities to grow and develop through professional development. Teachers directly referenced such opportunities as factors in which they believe teachers have decided to remain in the Kingfisher School District. 
    more » « less
  4. This paper presents a case study of a successful district effort to retain novice science teachers, drawn from a larger national project. The Mulberry School District (pseudonym) had one of the highest five-year retention rates of novice science teachers in the state for teachers hired between 2007–2012, with the majority of hires identifying as teachers of color. We conducted interviews with district teachers and administrators in this mixed methods study to identify five factors that likely influenced the high science teacher retention rate observed in the Mulberry Public School District. These were: (1) a competitive salary, (2) caring colleagues, (3) a culturally protected environment and community for teachers of color, (4) professional autonomy, and (5) opportunities for professional growth. 
    more » « less
  5. This paper presents the framework of teacher embeddedness, borrowed from the theory of job embeddedness used in economics and applied psychology, and applies it to the unique circumstances of teachers in order to help better understand reasons for teacher retention. Used as a theoretical framework for studying teacher retention, teacher embeddedness consists of three components—links, fit, and assets—which are examined through the lens of both the school organization and the community. The analytic power of this framework is demonstrated with an analysis of the challenges of teacher retention during the COVID-19 global pandemic, as an example of its promise to inform supports for teachers during a time for radical change in many teachers’ work and home lives. 
    more » « less
  6. null (Ed.)