## Publications

89 results found

Chernyshenko SI, Zhang C, Butt H,
et al., 2019, A large-scale filter for applications of QSQH theory of scale interactions in near-wall turbulence, *FLUID DYNAMICS RESEARCH*, Vol: 51, ISSN: 0169-5983

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- Citations: 1

Ghebali S, Chernyshenko SI, Leschziner MA, 2019, Turbulent-drag reduction by oblique wavy wall undulations, ERCOFTAC Series, Pages: 545-551

© Springer Nature Switzerland AG 2019. Reducing the turbulent skin-friction drag over civilian aircraft is a potentially high-reward target, as this drag component accounts for about half of the total drag in cruise conditions. Thus, even modest reductions convert into material savings, resulting in significant cuts in costs. Active-control techniques can be remarkably effective at suppressing turbulence and drag, but pose major engineering challenges in terms of actuation, efficient operation, reliability and maintainability. In contrast, passive techniques based on riblets are easier to implement, but face important durability and maintenance limitations related to the extremely small spacing of the grooves. The alternative passive-control method that is the subject of the present paper was first proposed in Chernyshenko (Drag reduction by a solid wavy wall emulating spanwise oscillations. Part 1. [physics.flu-dyn](arXiv:1304.4638 ), (2013), [1]). The key characteristic of the method is that it involves wavy surface undulations directed obliquely to the mean flow and having wave lengths two orders of magnitude larger than riblets, and would thus be much more practical to manufacture and maintain.

Huang D, Jin B, Lasagna D,
et al., 2017, Expensive Control of Long-Time Averages Using Sum of Squares and Its Application to A Laminar Wake Flow, *IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY*, Vol: 25, Pages: 2073-2086, ISSN: 1063-6536

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- Citations: 2

Ghebali S, Chernyshenko SI, Leschziner MA, 2017, Can large-scale oblique undulations on a solid wall reduce the turbulent drag?, *PHYSICS OF FLUIDS*, Vol: 29, ISSN: 1070-6631

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- Citations: 5

Ghebali S, Chernyshenko SI, Leschziner MA, Can large-scale oblique undulations on a solid wall reduce the turbulent drag?, *Physics of Fluids*, Vol: 29, Pages: 105102-105102

Direct numerical simulations of fully-developed turbulent channel flows withwavy walls are undertaken. The wavy walls, skewed with respect to the mean flowdirection, are introduced as a means of emulating a Spatial Stokes Layer (SSL)induced by in-plane wall motion. The transverse shear strain above the wavywall is shown to be similar to that of a SSL, thereby affecting the turbulentflow, and leading to a reduction in the turbulent skin-friction drag. Thepressure- and friction-drag levels are carefully quantified for various flowconfigurations, exhibiting a combined maximum overall-drag reduction of about0.5%. The friction-drag reduction is shown to behave approximatelyquadratically for small wave slopes and then linearly for higher slopes, whilstthe pressure-drag penalty increases quadratically. Unlike in the SSL case,there is a region of increased turbulence production over a portion of thewall, above the leeward side of the wave, thus giving rise to a local increasein dissipation. The transverse shear-strain layer is shown to be approximatelyReynolds-number independent when the wave geometry is scaled in wall units.

Ghebali S, Chernyshenko S, Leschziner M, 2017, Turbulent drag reduction by wavy wall, 10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017

Fully-developed turbulent flow in channels with oblique wavy walls is analysed, from a drag-reduction perspective, by means of Direct Numerical Simulations (DNS). The wavy geometry is chosen to emulate the shear strain produced by a Spatial Stokes Layer (SSL) generated by oscillatory wall motion. As the cost of performing a parametric optimisation is prohibitive, an alternate solution is presented, based on a linear model of a perturbed plane-channel flow, using a turbulent viscosity. Flow properties and levels of drag reduction or increase are reported for various configurations.

Chernyshenko S, 2017, Relationship between the methods of bounding time averages

The problem of finding bounds of time-averaged characteristics of dynamicalsystems, such as for example the bound on the mean energy dissipation rate in aturbulent flow governed by incompressible Navier-Stokes equations, isconsidered. It is shown that both the well-known background flow method ofDoering and Constantin and the direct method proposed by Seis in 2015correspond to the same quadratic storage functional in the framework of theindefinite storage functional method. In particular, a background flow can befound corresponding to the linear functional used in the direct method and viceversa. It is shown that any bound obtained with the background flow method canalso be obtained by the direct method. The reverse is true subject to anadditional constraint. The relative advantages of the three methods arediscussed.

Chernyshenko SI, Zhang C, Butt H, et al., 2017, Extrapolating statistics of turbulent flows to higher Re using quasi-steady theory of scale interaction in near-wall turbulence, 10th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2017

A new technique for extrapolating statistical characteristics of near-wall turbulence from medium to higher Re is outlined. Results for extrapolating the velocity two-point correlation from Reτ= 2003 to Reτ= 4179 and for the parameters of an optimized comb probe for detecting the large-scale velocity component required for applying the technique in practice are presented.

Lasagna D, Huang D, Tutty OR,
et al., 2016, Sum-of-squares approach to feedback control of laminar wake flows, *JOURNAL OF FLUID MECHANICS*, Vol: 809, Pages: 628-663, ISSN: 0022-1120

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- Citations: 2

Fantuzzi G, Goluskin D, Huang D,
et al., 2016, Bounds for deterministic and stochastic dynamical systems using sum-of-squares optimization, *SIAM Journal on Applied Dynamical Systems*, Vol: 15, Pages: 1962-1988, ISSN: 1536-0040

We describe methods for proving upper and lower bounds on inﬁnite-time averages in deterministic dynamical systems and on stationary expectations in stochastic systems. The dynamics and the quantities to be bounded are assumed to be polynomial functions of the state variables. The methods are computer-assisted, using sum-of-squares polynomials to formulate suﬃcient conditions that can be checked by semideﬁnite programming. In the deterministic case, we seek tight bounds that apply to particular local attractors. An obstacle to proving such bounds is that they do not hold globally; they are generally violated by trajectories starting outside the local basin of attraction. We describe two closely related ways past this obstacle: one that requires knowing a subset of the basin of attraction, and another that considers the zero-noise limit of the corresponding stochastic system. The bounding methods are illustrated using the van der Pol oscillator. We bound deterministic averages on the attracting limit cycle above and below to within 1%, which requires a lower bound that does not hold for the unstable ﬁxed point at the origin. We obtain similarly tight upper and lower bounds on stochastic expectations for a range of noise amplitudes. Limitations of our methods for certain types of deterministic systems are discussed, along with prospects for improvement.

Zhang C, Chernyshenko SI, 2016, Quasisteady quasihomogeneous description of the scale interactions in near-wall turbulence, *PHYSICAL REVIEW FLUIDS*, Vol: 1, ISSN: 2469-990X

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- Citations: 20

Lasagna D, Tutty OR, Chernyshenko S, 2016, Flow regimes in a simplified Taylor-Couette-type flow model, *EUROPEAN JOURNAL OF MECHANICS B-FLUIDS*, Vol: 57, Pages: 176-191, ISSN: 0997-7546

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- Citations: 1

Fantuzzi G, Goluskin D, Huang D,
et al., 2016, Bounds for Deterministic and Stochastic Dynamical Systems using Sum-of-Squares Optimization, *SIAM JOURNAL ON APPLIED DYNAMICAL SYSTEMS*, Vol: 15, Pages: 1962-1988, ISSN: 1536-0040

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- Citations: 7

Huang D, Chernyshenko S, 2016, LONG-TIME AVERAGE COST CONTROL OF POLYNOMIAL SYSTEMS: A SUM-OF-SQUARES-BASED SMALL-FEEDBACK APPROACH, 8th ASME Annual Dynamic Systems and Control Conference (DSCC 2015), Publisher: AMER SOC MECHANICAL ENGINEERS

Lasagna D, Huang D, Tutty OR, et al., 2016, Controlling Fluid Flows with Positive Polynomials, 35th Chinese Control Conference (CCC), Publisher: IEEE, Pages: 1301-1306, ISSN: 2161-2927

Huang D, Chernyshenko S, Goulart P,
et al., 2015, Sum-of-squares of polynomials approach to nonlinear stability of fluid flows: an example of application, *PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES*, Vol: 471, ISSN: 1364-5021

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- Citations: 6

Huang D, Chernyshenko S, 2015, Low-order State-feedback Controller Design for Long-time Average Cost Control of Fluid Flow Systems: A Sum-of-squares Approach, 34th Chinese Control Conference (CCC), Publisher: IEEE, Pages: 2479-2484, ISSN: 2161-2927

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- Citations: 1

Huang D, Chernyshenko S, Lasagna D, et al., 2015, Long-time Average Cost Control of Polynomial Systems: A Sum of Squares Approach, European Control Conference (ECC), Publisher: IEEE, Pages: 3244-3249

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- Citations: 1

Huang D, Chernyshenko S, 2015, Long-time Average Cost Control of Stochastic Systems Using Sum of Squares of Polynomials, 34th Chinese Control Conference (CCC), Publisher: IEEE, Pages: 2344-2349, ISSN: 2161-2927

Chernyshenko SI, Goulart P, Huang D,
et al., 2014, Polynomial sum of squares in fluid dynamics: a review with a look ahead, *PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES*, Vol: 372, ISSN: 1364-503X

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- Citations: 19

Chernyshenko S, Huang D, Goulart P, et al., 2013, Nonlinear Stability Analysis of Fluid Flow using Sum of Squares of Polynomials, 11th International Conference of Numerical Analysis and Applied Mathematics (ICNAAM), Publisher: AMER INST PHYSICS, Pages: 265-268, ISSN: 0094-243X

Vodop'yanov IS, Nikitin NV, Chernyshenko SI, 2013, Turbulent drag reduction by spanwise oscillations of a ribbed surface, *FLUID DYNAMICS*, Vol: 48, Pages: 461-470, ISSN: 0015-4628

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- Citations: 1

Blesbois O, Chernyshenko SI, Touber E,
et al., 2013, Pattern prediction by linear analysis of turbulent flow with drag reduction by wall oscillation, *JOURNAL OF FLUID MECHANICS*, Vol: 724, Pages: 607-641, ISSN: 0022-1120

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- Citations: 12

Chernyshenko S, 2013, Drag reduction by a solid wall emulating spanwise oscillations. Part 1

A new idea for turbulent skin-friction reduction is proposed, wherein theshape of the solid wall is designed to create the spanwise pressure gradientacting similarly to the well-known method of drag reduction by in-planespanwise wall motion. Estimates based on the assumption of similarity with dragreduction effect of in-plane wall motion suggest that drag reduction of about2.4% can be achieved in the flow past a wavy wall, with the crests forming anangle of about 38 degrees with the main flow direction, and the wave period inthe main flow direction equal to about 1500 wall units. The required height ofthe wall waves have to be adjusted to achieve the same intensity of thespanwise motion as that created by an in-plane moving wall of the samewavelength and with peak wall velocity equal to 2 wall units. Further researchis being conducted in order to determine this height. Suggestions are made forfurther research on confirming the feasibility of the proposed method and onoptimising the wall shape.

Mathis R, Marusic I, Chernyshenko SI,
et al., 2013, Estimating wall-shear-stress fluctuations given an outer region input, *JOURNAL OF FLUID MECHANICS*, Vol: 715, Pages: 163-180, ISSN: 0022-1120

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- Citations: 63

Duque-Daza CA, Baig MF, Lockerby DA,
et al., 2012, Modelling turbulent skin-friction control using linearized Navier-Stokes equations, *JOURNAL OF FLUID MECHANICS*, Vol: 702, Pages: 403-414, ISSN: 0022-1120

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- Citations: 16

Chernyshenko SI, Marusic I, Mathis R, 2012, Quasi-steady description of modulation effects in wall turbulence

A theoretical description of the phenomenon of modulation of near-wallturbulence by large scale structures is investigated. The description given issimple in that the effect of large-scale structures is limited to aquasi-steady response of the near-wall turbulence to slow large-scalefluctuations of the skin friction. The most natural and compact form ofexpressing this mechanism is given by the usual Reynolds-number-independentrepresentation of the total skin friction and velocity, scaled in wallvariables, where the mean quantities are replaced by large-scalelow-pass-filtered fluctuating components. The theory is rewritten in terms offuctuations via a universal mean velocity and random mean square fluctuationvelocity profiles of the small-scales and then linearised assuming that thelarge-scale fluctuations are small as compared to the mean components. Thisallows us to express the superposition and modulation coefficients of theempirical predictive models of the skin friction and streamwise fluctuatingvelocity given respectively by Marusic et al. (13th Eur. Turb. Conf., 2011) andMathis et al. (J. Fluid Mech. 2011, vol. 681, pp. 537-566). It is found thatthe theoretical quantities agree well with experimentally determinedcoefficients.

Goulart PJ, Chernyshenko S, 2012, Global stability analysis of fluid flows using sum-of-squares, *PHYSICA D-NONLINEAR PHENOMENA*, Vol: 241, Pages: 692-704, ISSN: 0167-2789

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- Citations: 19

Booker CD, Zhang X, Chernyshenko SI, 2011, Large-Scale Vortex Generation Modeling, *JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME*, Vol: 133, ISSN: 0098-2202

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- Citations: 1

Wang HL, Nikitin NV, Chernyshenko SI, 2011, Identification of a Laminar-Turbulent Interface in Partially Turbulent Flow, *FLUID DYNAMICS*, Vol: 46, Pages: 911-916, ISSN: 0015-4628

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