13 research outputs found
Virtual wall oscillations forced by a dbd plasma actuator operating under beat frequency – a concept for turbulent drag reduction
No full textA modified concept for generating DBD-based virtual spanwise wall oscillations is introduced in continuation of earlier efforts by Hehner et al. (2019) ["Stokes-layer formation under absence of moving parts – A novel oscillatory plasma actuator design for turbulent drag reduc-tion", Phys. Fluids 31, 051701]. Four groups of a multi-electrode actuator array are operated at interfering high-voltage signals to achieve an oscillating discharge intensity at 50 Hz beat frequency. The resulting velocity fields have been recorded with time-resolved planar high-speed particle image velocimetry so as to analyse the induced flow topology and wall-normal velocity profiles. A direct comparison of the results to Hehner et al. (2019) has indicated favourable effects of the new concept in terms of flow topology (i.e improved spanwise flow homogeneity, velocity magnitude increase and reduced lift-off), which renders the new operation concept of the actuator array particularly promising for Stokes-layer-like flow formations and, consequently, for turbulent drag reduction over a range of Reynolds numbers.Aerodynamic
How to boost soundscapes with tax breaks—On the application of Henry George’s environmental economics to noise annoyance
No full text
Effects of actuation mode on plasma-induced spanwise flow oscillations
No full textTwo different plasma actuation strategies for producing near-wall flow oscillations, namely the burst-modulation and beat-frequency mode, are characterized with planar particle image velocimetry in quiescent air. Both concepts are anticipated to work as non-mechanical surrogates of oscillating walls aimed at turbulent flow drag reduction, with the added benefit of no moving parts, as the fluid is purely manipulated by plasma-generated body forces. The current work builds upon established flow-control and proof-of-concept demonstrators, as such, delivering an in-depth characterization of cause and impact of the plasma-induced flow oscillations. Various operational parameter combinations (oscillation frequency, duty cycle and input body force) are investigated. A universal performance diagram that is valid for plasma-based oscillations, independent of the actuation concept is derived. Results show that selected combinations of body force application methods suffice to reproduce oscillating wall dynamics from experimental data. Accordingly, the outcomes of this work can be exploited to create enhanced actuation models for numerical simulations of plasma-induced flow oscillations, by considering the body force as a function of the oscillation phase. Furthermore, as an advantage over physically displaced walls, the exerted body force appears not to be hampered by resonances and therefore remains constant independent of the oscillation frequency. Hence, the effects of individual parameter changes on the plasma actuator performance and fluid response as well as strategies to avoid undesired effects can be determined. AerodynamicsFlow Physics and Technolog
Swept-wing transition control using DBD plasma actuators
No full textIn the present work, laminar flow control, following the discrete roughness elements (DRE) strategy, also called upstream flow deformation (UFD) was applied on a 45◦ swept-wing at a chord Reynold’s number of Rec = 2.1 · 106 undergoing cross-flow instability (CFI) induced transition. Dielectric barrier discharge (DBD) plasma actuation was employed at a high frequency (fac = 10kHz) for this purpose. Specialized, patterned actuators that generate spanwinse-modulated plasma jets were fabricated using spray-on techniques and positioned near the leading edge. An array of DREs was installed upstream of the plasma forcing to lock the origin and evolution of critical stationary CFI vortices in the boundary layer. Two forcing configurations were investigated-in the first configuration the plasma jets were directly aligned against the incoming CF vortices while in the second the CF vortices passed between adjacent plasma jets. Infrared thermography was used to inspect transition location, while quantitative measurements of the boundary layer were obtained using particle image velocimetry. The obtained results show that the plasma forcing reduces the amplitude of stationary CF modes, thus delaying laminar-to-turbulent transition. In contrast to previous efforts [1], the plasma forcing did not introduce unsteady fluctuations into the boundary layer. The mechanism responsible for the observed transition delay appears to leverage more on localised base-flow modification rather than the DRE/UFD control strategy.Aerodynamic
Boundary Algebra: A Simple Notation for Boolean Algebra and the Truth Functors
No full textBoundary algebra [BA] is a simpler notation for Spencer-Brown’s (1969) primary algebra [pa], the Boolean algebra 2, and the truth functors. The primary arithmetic [PA] consists of the atoms ‘()’ and the blank page, concatenation, and enclosure between ‘(‘ and ‘)’, denoting the primitive notion of distinction. Inserting letters denoting the presence or absence of () into a PA formula yields a BA formula. The BA axioms are "()()=()" (A1), and "(()) [=?] may be written or erased at will” (A2). Repeated application of these axioms to a PA formula yields a member of B= {(),?} called its simplification. (a) has two intended interpretations: (a) ? a? (Boolean algebra 2), and (a) ? ~a (sentential logic). BA is self-dual: () ? 1 [dually 0] so that B is the carrier for 2, ab ? a?b [a?b], and (a)b [(a(b))] ? a=b, so that ?=() [()=?] follows trivially and B is a poset. The BA basis abc= bca (Dilworth 1938), a(ab)= a(b), and a()=() (Bricken 2002) facilitates clausal reasoning and proof by calculation. BA also simplifies normal forms and Quine’s (1982) truth value analysis. () ? true [false] yields boundary logic.G. Spencer Brown; boundary algebra; boundary logic; primary algebra; primary arithmetic; Boolean algebra; calculation proof; C.S. Peirce; existential graphs.
Experimental control of swept-wing transition through base-flow modification by plasma actuators
No full textControl of laminar-to-turbulent transition on a swept-wing is achieved by base-flow modification in an experimental framework, up to a chord Reynolds number of 2.5 million. This technique is based on the control strategy used in the numerical simulation by Dörr & Kloker (J. Phys. D: Appl. Phys., vol. 48, 2015b, 285205). A spanwise uniform body force is introduced using dielectric barrier discharge plasma actuators, to either force against or along the local cross-flow component of the boundary layer. The effect of forcing on the stability of the boundary layer is analysed using a simplified model proposed by Serpieri et al. (J. Fluid Mech., vol. 833, 2017, pp. 164–205). A minimal thickness plasma actuator is fabricated using spray-on techniques and positioned near the leading edge of the swept-wing, while infrared thermography is used to detect and quantify transition location. Results from both the simplified model and experiment indicate that forcing along the local cross-flow component promotes transition while forcing against successfully delays transition. This is the first experimental demonstration of swept-wing transition delay via base-flow modification using plasma actuators.Aerodynamic
The representation of trauma in narrative : a study of six late twentieth century novels
No full textThis thesis conducts a close analysis of representations of trauma in six
late twentieth century novels. I construct a theoretical framework by examining
debates about trauma and narrative which have taken place in the fields of
historiography, social studies, psychoanalysis and literary fiction. By drawing on
these debates, I argue that the relationship between narrative and trauma is
paradoxical: narrative is an essential tool, both for working-through and bearing
witness to the trauma, but it can also intentionally or unintentionally be used to
create an inauthentic version of events.
I illustrate the need felt by many late twentieth century theorists for the
development of a narrative form that will be able to produce an effective version
of trauma. This narrative needs to facilitate working-through and enable
witnessing of trauma. However, it must strive to avoid producing a falsifying
version of the trauma. I argue that it can achieve this by acknowledging its own
provisionality and therefore highlighting the limitations but also the necessity of
narrative representations of trauma.
I argue that the six contemporary novels I have chosen are examples of
narratives that strive to develop a more effective means of representing trauma.
The novels explore their concerns about trauma and narrative on both a thematic
and formal level. The story told in each novel follows a similar pattern of events:
in each novel the protagonist is depicted as suffering from the effects of trauma;
they all try to evade their traumas by creating falsifying versions of their
experiences; and they all offered a means of interpreting which will allow them to
work-though and, therefore, bear witness to their traumas. Finally, the six authors
utilise their narrative strategies to teach their readers this therapeutic and ethical
hermeneutics which corresponds with contemporary concerns about trauma and
narrative
Parthenolide: From plant shoots to cancer roots
No full textParthenolide (PTL), a sesquiterpene lactone (SL) originally purified from the shoots of feverfew (Tanacetum parthenium), has shown potent anticancer and anti-inflammatory activities. It is currently being tested in cancer clinical trials. Structure-activity relationship (SAR) studies of parthenolide revealed key chemical properties required for biological activities and epigenetic mechanisms, and led to the derivatization of an orally bioavailable analog, dimethylamino-parthenolide (DMAPT). Parthenolide is the first small molecule found to be selective against cancer stem cells (CSC), which it achieves by targeting specific signaling pathways and killing cancer from its roots. In this review, we highlight the exciting journey of parthenolide, from plant shoots to cancer roots. © 2013 Elsevier Ltd. 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