Control of a Semi-Circular Planform Wing in a "Gusting" Unsteady Free Stream Flow II: Modeling and Feedback Design

Active flow control has been demonstrated in Part I of this article to modify the lift, drag and pitching moments on a semi-circular wing during "gusting" flow conditions. The low aspect ratio wing, AR = 2.54, is mounted on a captive trajectory system that responds to the instantaneous lift force and pitching moment and the "gusting" flow is simulated by a 0.2 Hz oscillation of the free stream speed of the wind tunnel. The mean chord Reynolds number of the wing is 70,600. Active flow control occurs along the leading edge of the airfoil, which contains 16 spatially localized micro-valve actuators. Details of the experimental setup, a quasi steady state lift model and results involving open-loop proof of concept validation are provided in Part I of this paper. Here we outline principles and considerations associated with close loop design that will be discussed in our talk

Lift Response of a Stalled Wing to Pulsatile Disturbances

The transient lift response of a low-Reynolds-number wing subjected to small amplitude pulsatile disturbances is investigated. The wing has a small aspect ratio and a semicircular planform, and it is fully stalled at a 20 deg angle of attack. Microvalve actuators distributed along the leading edge of the wing produce the transient disturbance. It is shown that the lift response to a single pulse increases with increasing actuator supply pressure and that the lift response curves are similar to each other when scaled by the total impulse. Furthermore, for fixed actuator supply pressure, the amplitude and total impulse of the transient lift response curve increases with increasing external flow speed. In this case, the lift response curves are similar when scaled by the dynamic pressure. The lift response to a single pulse can be treated as a filter kernel, and it can be used to predict the lift time history for the arbitrary actuator input signals. The kernel is similar in shape to transient measurements obtained by other investigators on two-dimensional wings and flaps. Comparisons between the model predictions and the experiments using multiple pulse inputs and square-wave modulated input signals at low frequencies are presented

R.D., T.L., G.C., B. Treadwell to Isaac McFarron, 26 August 1844

https://egrove.olemiss.edu/aldrichcorr_b/1073/thumbnail.jp

A Finite-Time Thermodynamics of Unsteady Fluid Flows

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Turbulent fluid has often been conceptualized as a transient thermodynamic phase. Here, a finite-time thermodynamics (FTT) formalism is proposed to compute mean flow and fluctuation levels of unsteady incompressible flows. The proposed formalism builds upon the Galerkin model framework, which simplifies a continuum 3D fluid motion into a finite-dimensional phase-space dynamics and, subsequently, into a thermodynamics energy problem. The Galerkin model consists of a velocity field expansion in terms of flow configuration dependent modes and of a dynamical system describing the temporal evolution of the mode coefficients. Each mode is treated as one thermodynamic degree of freedom, characterized by an energy level. The dynamical system approaches local thermal equilibrium (LTE) where each mode has the same energy if it is governed only by internal (triadic) mode interactions. However, in the generic case of unsteady flows, the full system approaches only partial LTE with unequal energy levels due to strongly mode-dependent external interactions. The FTT model is first illustrated by a traveling wave governed by a 1D Burgers equation. It is then applied to two flow benchmarks: the relatively simple laminar vortex shedding, which is dominated by two eigenmodes, and the homogeneous shear turbulence, which has been modeled with 1459 modes

Reduced order Galerkin models of flow around NACA‐0012 airfoil

The construction of low‐dimensional models of the flow, containing only reduced number of degrees of freedom, is the essential prerequisite of closed‐loop control of that flow. Presently used models usually base on the Galerkin method, where the flow is approximated by the number of modes and coefficients. The velocities are computed from a system of ordinary differential equations, called Galerkin System, instead of Navier‐Stokes equation. In this paper, reduced order models of the flow around NACA‐0012 airfoil are presented. The chosen mode sets include POD modes from Karhunen‐Loeve decomposition (which require previous direct numerical simulation), as well as different eigenmodes from global stability analysis of the flow. First Published Online: 14 Oct 201

Control of a Semi-Circular Planform Wing in a "Gusting" Unsteady Freestream Flow: I - Experimental Issues

Active flow control is used to modify the lift, drag and pitching moments on a semicircular wing during "gusting" flow conditions. A longitudinal oscillating flow component has an amplitude of 10 percent of the freestream speed and a frequency giving k = 0.048 (f = 0.2 Hz). The aspect ratio of the wing is AR = 2.54, and the chord Reynolds number of the wing is 70,600. Pulsed-blowing flow control actuation occurs along the leading edge of the airfoil via 16 spatially localized micro-valve actuators. Feed-forward control based on a quasi-steady lift model is used to stabilize lift fluctuations generated by an oscillating free stream, which simulates the longitudinal component of a gusting flow. The quasi-steady system model reduces the amplitude of the fundamental and first harmonics of lift oscillations, but does not account for time delays. The time delay between the lift and the freestream oscillation was measured to be τ_(u)^(+) = 4.8. The time delay between the lift and the actuator input signal was found to be τ_(a)^(+) = 11.3

Quiescience as a mechanism for cyclical hypoxia and acidosis

Tumour tissue characteristically experiences fluctuations in substrate supply. This unstable microenvironment drives constitutive metabolic changes within cellular populations and, ultimately, leads to a more aggressive phenotype. Previously, variations in substrate levels were assumed to occur through oscillations in the hæmodynamics of nearby and distant blood vessels. In this paper we examine an alternative hypothesis, that cycles of metabolite concentrations are also driven by cycles of cellular quiescence and proliferation. Using a mathematical modelling approach, we show that the interdependence between cell cycle and the microenvironment will induce typical cycles with the period of order hours in tumour acidity and oxygenation. As a corollary, this means that the standard assumption of metabolites entering diffusive equilibrium around the tumour is not valid; instead temporal dynamics must be considered

On least-order flow representations for aerodynamics and aeroacoustics

We propose a generalization of proper orthogonal decomposition (POD) for optimal flow resolution of linearly related observables. This Galerkin expansion, termed ‘observable inferred decomposition' (OID), addresses a need in aerodynamic and aeroacoustic applications by identifying the modes contributing most to these observables. Thus, OID constitutes a building block for physical understanding, least-biased conditional sampling, state estimation and control design. From a continuum of OID versions, two variants are tailored for purposes of observer and control design, respectively. Firstly, the most probable flow state consistent with the observable is constructed by a ‘least-residual' variant. This version constitutes a simple, easily generalizable reconstruction of the most probable hydrodynamic state to preprocess efficient observer design. Secondly, the ‘least-energetic' variant identifies modes with the largest gain for the observable. This version is a building block for Lyapunov control design. The efficient dimension reduction of OID as compared to POD is demonstrated for several shear flows. In particular, three aerodynamic and aeroacoustic goal functionals are studied: (i)lift and drag fluctuation of a two-dimensional cylinder wake flow; (ii)aeroacoustic density fluctuations measured by a sensor array and emitted from a two-dimensional compressible mixing layer; and (iii)aeroacoustic pressure monitored by a sensor array and emitted from a three-dimensional compressible jet. The most ‘drag-related', ‘lift-related' and ‘loud' structures are distilled and interpreted in terms of known physical processe

Meningkatkan Kemampuan Bahasa Inggris Siswa Melalui Model Pembelajaran Kooperatif Tipe Think Pair and Share (TPS) Berbasis Karya Sastra pada Sekolah Menengah Pertama di Kota Makassar

Ringkasan: Kurikulum Tingkat Satuan Pendidikan (KTSP) dalam pelaksanaannya lebih cenderung kepada pendekatan Manajemen Berbasis Sekolah (MBS) atau desentralisasi; guru mengembangkan KTSP dan silabusnya berdasarkan kerangka dasar kurikulum dan standar kompetensi lulusan dari Standar Nasional Pendidikan. Bahasa Inggris untuk satuan tingkat pendidikan menengah termasuk mata pelajaran wajib yang harus diajarkan kepada para siswa di SMP. Apakah pembelajaran bahasa Inggris menggunakan kooperatif learning, Tipe Think Pair ami Share (TPS) berbasis karya sastra dapat meningkatkan kemampuan bahasa Inggris siswa? Penelitian ini bertujuan untuk mengetahui apakah pembelajaran bahasa Inggris menggunakan kooperatif learning. Tipe. Think Pair and Share (TPS) berbasis karya sastra dapat meningkatkan kemampuan bahasa Inggris siswa. Penelitian Hasil penelitian menunjukkan bahwa pembelajaran bahasa Inggris pada Sekolah Menengah Pertama pada SMP Negeri 36 Makassar menggunakan model pembelajaran kooperatif learning, Tipe Think Pair and Share f TPS) berbasis karya sastra dapat meningkatkan kemampuan bahasa Inggris siswa