Trailing Edge Noise Reduction by Passive and Active Flow Controls

This paper presents the results on the use of porous metal foams (passive control) and dielectric barrier surface plasma actuations (active control) for the reduction of vortex shedding tonal noises from the nonflat plate type trailing edge serration in a NACA0012 airfoil previously discussed in Chong et al. (AIAA J. Vol. 51, 2013, pp. 2665-2677). The use of porous metal foams to fill the interstices between adjacent members of the sawtooth can almost completely suppress the vortex shedding tonal noise, whilst the serration effect on the broadband noise reduction is retained. This concept will promote the nonflat plate type serrated trailing edge to become a genuine alternative to the conventional flat plate type serrated trailing edge, which is known to have drawbacks in the structural stability, aerodynamic performances and implementation issues. For the plasma actuators, configuration which produces electric wind in a tangential direction is found to be not very effective in suppressing the vortices emanated from the serration blunt root. On the other hand, for the plasma configuration which produces electric wind in a vertical direction, good level of vortex shedding tonal noise reduction has been demonstrated. However, the self noise produced by the plasma actuators negates the noise benefits on the tonal noise reduction. This characteristic illustrates the need to further develop the plasma actuators in a two pronged approach. First is to increase the electric wind speed, thereby allowing the plasma actuators to be used in a higher free jet velocity which naturally produces a larger level of jet noise. Second, the self noise radiated by the plasma actuators should be reduced

Dynamics in a supercooled liquid of symmetric dumbbells: Reorientational hopping for small molecular elongations

We present extensive molecular dynamics simulations of a liquid of symmetric dumbbells, for constant packing fraction, as a function of temperature and molecular elongation. For large elongations, translational and rotational degrees of freedom freeze at the same temperature. For small elongations only the even rotational degrees of freedom remain coupled to translational motions and arrest at a finite common temperature. The odd rotational degrees of freedom remain ergodic at all investigated temperature and the temperature dependence of the corresponding characteristic time is well described by an Arrhenius law. Finally, we discuss the evidence in favor of the presence of a type-A transition temperature for the odd rotational degrees of freedom, distinct from the type-B transition associated with the arrest of the translational and even rotational ones, as predicted by the mode-coupling theory for the glass transition.Comment: 4 pages, 3 figure

From zonal flow to convection rolls in Rayleigh-B\'enard convection with free-slip plates

Rayleigh-B\'enard (RB) convection with free-slip plates and horizontally periodic boundary conditions is investigated using direct numerical simulations. Two configurations are considered, one is two-dimension (2D) RB convection and the other one three-dimension (3D) RB convection with a rotating axis parallel to the plate. We explore the parameter range of Rayleigh numbers Ra from $10^7 to$10^9$and Prandtl numbers$Pr$from$1$to$100. We show that zonal flow, which was observed, for example, by Goluskin \emph{et al}. \emph{J. Fluid. Mech.} 759, 360-385 (2014) for \Gamma=2$, is only stable when$\Gamma$is smaller than a critical value, which depends on$Ra$and$Pr$. With increasing$\Gamma$, we find a second regime in which both zonal flow and different convection roll states can be statistically stable. For even larger$\Gamma$, in a third regime, only convection roll states are statistically stable and zonal flow is not sustained. For the 3D simulations, we fix$Ra=10^7$and$Pr=0.71$, and compare the flow for$\Gamma=8$and$\Gamma = 16$. We demonstrate that with increasing aspect ratio$\Gamma$, zonal flow, which was observed for small$\Gamma=2\pi by von Hardenberg \emph{et al}. \emph{Phys. Rev. Lett.} 15, 134501 (2015), completely disappears for \Gamma=16$. For such large$\Gamma$only convection roll states are statistically stable. In between, here for medium aspect ratio$\Gamma = 8$, the convection roll state and the zonal flow state are both statistically stable. What state is taken depends on the initial conditions, similarly as we found for the 2D case.Comment: 26 pages, 12 figure

Top quark rare three-body decays in the littlest Higgs model with T-parity

In the littlest Higgs model with T-parity (LHT), the mirror quarks have flavor structures and will contribute to the top quark flavor changing neutral current. In this work, we perform an extensive investigation of the top quark rare three-body decays $t\to cVV (V=\gamma,Z,g)$ and $t\to cf\bar{f} (f=b,\tau,\mu,e)$ at one-loop level. Our results show that the branching ratios of $t\to cgg$ and $t\to cb\bar{b}$ could reach $\mathcal {O}(10^{-3})$ in the favorite parameter space of the littlest Higgs model with T-parity, which implies that these decays may be detectable at the LHC or ILC, while for the other decays, their rates are too small to be observable at the present or future colliders.Comment: 12 pages, 10 figure

Photon-induced production of the mirror quarks from the LHTLHT model at the LHCLHC

The photon-induced processes at the $LHC$ provide clean experimental conditions due to absence of the proton remnants, which might produce complementary and interesting results for tests of the standard model and for searching of new physics. In the context of the littlest $Higgs$ model with T-parity, we consider the photon-induced production of the mirror quarks at the $LHC$. The cross sections for various production channels are calculated and a simply phenomenology analysis is performed by assuming leptonic decays.Comment: 20 pages, 10 figure

The development of turbulent pipe flow

Whilst turbulence still remains one of the great mysteries of classical physics, its reputation for a chaotic lack of structure is under intense scrutiny. Research now points to the existence of highly organized large-scale structures within turbulent flows. Much of this research have almost exclusively been carried out within a so called fully-developed region of flow. This region is downstream of a point beyond which the flow field’s behavior is invariant. However, it has not been conclusively proven that a fully developed region actually exists. A literature survey found that most facilities are cited as being ‘sufficiently long’, yet no formal definition or documentary evidence of the fully developed condition is widely accepted. The aim of the study is to produce a detailed analysis of the flow from the uniform inlet conditions through to the fully-developed turbulent state, along with an accurate definition of what constitutes fully developed flow. This investigation concerns the affect of both the growth of large-scale structures and their role in the evolution of the flow to the fully-developed condition. With the increasing acceptance of the turbulent large-scale structures model, previous research has not yet shown how large-scale structures affect this development length. These aims were achieved by the design, development and deployment of a carriage to transport hot-wires within the pipe allowing measurements at any stream wise point within the working sectio

Implementing Inquiry-based Learning and Examining the Effects in Junior College Probability Lessons

This study examined how Year 12 students use their inquiry skills in solving conditional probability questions by means of Inquiry-Based Learning application. The participants consisted of 66 students of similar academic abilities in Mathematics, selected from three classes, along with their respective teachers. Observational rubric and lesson observation checklist were used as the data collection instruments. The results obtained were analyzed and then quantitatively reported. Findings from the observational rubric revealed that Year 12 students were able to understand most of the questions during the activity, but they only select and use one previously learned method to solve the questions during the activity. In addition, these students rarely seek and asked probing questions during the activity. They only used words, diagrams and numbers to interpret the solutions to the questions and make connections between them but with few mistakes detected.DOI: http://dx.doi.org/10.22342/jme.8.2.3964.157-16

Investigation of passive flow control techniques to enhance the stall characteristics of a microlight aircraft

This report investigates the enhancement of aerodynamic stall characteristics of a Skyranger microlight aircraft by the use of passive flow control techniques, namely vortex generators and turbulators. Each flow control device is designed and scaled to application conditions. Force balance measurements and surface oil flow visualisation are carried out on a half-model of the microlight to further investigate the nature of the flow on the aircraft with and without the flow control devices. The results indicate a clear advantage to the use of turbulators compared with vortex generators. Turbulators increased the maximum lift coefficient by 2.8%, delayed the onset of stall by increasing the critical angle by 17.6% and reduced the drag penalty at both lower (pre-stall) and higher angles of attack by 8% compared to vortex generators. With vortex generators applied, the results indicated a delayed stall with an increase in the critical angle by 2% and a reduced drag penalty at higher angles of attack

Novelty Search in Competitive Coevolution

One of the main motivations for the use of competitive coevolution systems is their ability to capitalise on arms races between competing species to evolve increasingly sophisticated solutions. Such arms races can, however, be hard to sustain, and it has been shown that the competing species often converge prematurely to certain classes of behaviours. In this paper, we investigate if and how novelty search, an evolutionary technique driven by behavioural novelty, can overcome convergence in coevolution. We propose three methods for applying novelty search to coevolutionary systems with two species: (i) score both populations according to behavioural novelty; (ii) score one population according to novelty, and the other according to fitness; and (iii) score both populations with a combination of novelty and fitness. We evaluate the methods in a predator-prey pursuit task. Our results show that novelty-based approaches can evolve a significantly more diverse set of solutions, when compared to traditional fitness-based coevolution.Comment: To appear in 13th International Conference on Parallel Problem Solving from Nature (PPSN 2014