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Hanifi, Ardeshir, DocentORCID iD iconorcid.org/0000-0002-5913-5431
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Publications (10 of 114) Show all publications
Morra, P., Sasaki, K., Hanifi, A., Cavalieri, A. V. G. & Henningson, D. S. (2020). A realizable data-driven approach to delay bypass transition with control theory. Journal of Fluid Mechanics, 883, Article ID A33.
Open this publication in new window or tab >>A realizable data-driven approach to delay bypass transition with control theory
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2020 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 883, article id A33Article in journal (Refereed) Published
Abstract [en]

The current work presents a realizable method to control streaky disturbances in boundary layer flows and delay transition to turbulence by means of active flow control. Numerical simulations of the nonlinear transitional regime in a Blasius boundary layer are performed where streaks are excited in the boundary layer by means of a high level of free-stream turbulence. The occurring disturbances are measured by means of localized wall-shear-stress sensors and damped out using near-wall actuators, which resemble ring plasma actuators. Each actuator is powered by a time-varying signal whose amplitude is computed by processing signals from the sensors. The processed signal is the result of two control laws: the linear quadratic Gaussian regulator (LQG) and the inverse feed-forward control technique (IFFC). The use of the first control method, LQG, requires a state-space representation of the system dynamics, so the flow is described by means of a linear time-invariant operator that captures only the most relevant information of the dynamics and results in a reduced-order model (ROM). The ROM is computed by means of the eigensystem realization algorithm (ERA), which is based on the impulse responses of the real system. Collecting such impulse responses may be unfeasible when considering free-stream turbulence because of the high dimensionality of the input forcing needed for a precise description of such a phenomenon. Here, a new method to identify the relevant system dynamics and generate the needed impulse responses is proposed, based on additional shear-stress measurements in an upstream location. Transfer functions between such measurements and other downstream sensors are obtained and allow the derivation of the ERA system, in a data-driven approach that would be realizable in experiments. Finally, in order to discuss the advantages of the LQG based on the ROM and analyse its performance, the implemented LQG is compared to the IFFC, which consists of wave cancellation. The work (i) presents a systematic and straightforward way to deal with high-dimensional disturbances in order to build ROMs for a feasible control technique, and (ii) shows that even when considering practical constraints, such as the type and size of actuators and sensors, it is possible to achieve at least as large delay of bypass transition as that obtained in more idealized cases found in the literature.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS, 2020
Keywords
boundary layer control, drag reduction, transition to turbulence
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-267149 (URN)10.1017/jfm.2019.793 (DOI)000508121500033 ()
Note

QC 20200217

Available from: 2020-02-17 Created: 2020-02-17 Last updated: 2020-02-17Bibliographically approved
von Deyn, L. H., Forooghi, P., Frohnapfel, B., Schlatter, P., Hanifi, A. & Henningson, D. S. (2020). Direct Numerical Simulations of Bypass Transition over Distributed Roughness. AIAA Journal, 58(2), 702-711
Open this publication in new window or tab >>Direct Numerical Simulations of Bypass Transition over Distributed Roughness
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2020 (English)In: AIAA Journal, ISSN 0001-1452, E-ISSN 1533-385X, Vol. 58, no 2, p. 702-711Article in journal (Refereed) Published
Abstract [en]

Bypass transition in a boundary layer subjected to freestream turbulence and distributed surface roughness is studied numerically. The distributed surface roughness is reproduced with an immersed boundary technique, and the freestream turbulence is artificially generated by a superposition of eigenmodes of the Orr-Sommerfeld and Squire equations. Both an undisturbed laminar inflow and a disturbed inflow with freestream turbulence are studied. In either case a parametric study on the effects of the roughness size and density is carried out. The simulations reveal that the presence of roughness induces streaks in the laminar flow. When the freestream is turbulent, both roughness height and density show an impact on the onset of transition. The superposition of surface roughness and freestream turbulence causes amplified streaks. As a result, the streak instability occurs earlier within the boundary layer. The results show good qualitative and quantitative agreement to both experimental and numerical studies available in the literature.

Place, publisher, year, edition, pages
AMER INST AERONAUTICS ASTRONAUTICS, 2020
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-269475 (URN)10.2514/1.J057765 (DOI)000513533200015 ()
Note

QC 20200310

Available from: 2020-03-10 Created: 2020-03-10 Last updated: 2020-03-10Bibliographically approved
Chauvat, G., Peplinski, A., Henningson, D. S. & Hanifi, A. (2020). Global linear analysis of a jet in cross-flow at low velocity ratios. Journal of Fluid Mechanics, 889, Article ID A12.
Open this publication in new window or tab >>Global linear analysis of a jet in cross-flow at low velocity ratios
2020 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 889, article id A12Article in journal (Refereed) Published
Abstract [en]

The stability of the jet in cross-flow is investigated using a complete set-up including the flow inside the pipe. First, direct simulations were performed to find the critical velocity ratio as a function of the Reynolds number, keeping the boundary-layer displacement thickness fixed. At all Reynolds numbers investigated, there exists a steady regime at low velocity ratios. As the velocity ratio is increased, a bifurcation to a limit cycle composed of hairpin vortices is observed. The critical bulk velocity ratio is found at approximately for the Reynolds number , above which a global mode of the system becomes unstable. An impulse response analysis was performed and characteristics of the generated wave packets were analysed, which confirmed results of our global mode analysis. In order to study the sensitivity of this flow, we performed transient growth computations and also computed the optimal periodic forcing and its response. Even well below this stability limit, at , large transient growth ( in energy amplification) is possible and the resolvent norm of the linearized Navier-Stokes operator peaks above . This is accompanied with an extreme sensitivity of the spectrum to numerical details, making the computation of a few tens of eigenvalues close to the limit of what can be achieved with double precision arithmetic. We demonstrate that including the meshing of the jet pipe in the simulations does not change qualitatively the dynamics of the flow when compared to the simple Dirichlet boundary condition representing the jet velocity profile. This is in agreement with the recent experimental results of Klotz et al. (J. Fluid Mech., vol. 863, 2019, pp. 386-406) and in contrast to previous studies of Cambonie & Aider (Phys. Fluids, vol. 26, 2014, 084101). Our simulations also show that a small amount of noise at subcritical velocity ratios may trigger the shedding of hairpin vortices.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS, 2020
Keywords
boundary layer stability, jets
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-269438 (URN)10.1017/jfm.2020.85 (DOI)000514704100001 ()2-s2.0-85081086529 (Scopus ID)
Note

QC 20200316

Available from: 2020-03-16 Created: 2020-03-16 Last updated: 2020-03-16Bibliographically approved
Sasaki, K., Morra, P., Cavalieri, A. V. G., Hanifi, A. & Henningson, D. S. (2020). On the role of actuation for the control of streaky structures in boundary layers. Journal of Fluid Mechanics, 883, Article ID A34.
Open this publication in new window or tab >>On the role of actuation for the control of streaky structures in boundary layers
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2020 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 883, article id A34Article in journal (Refereed) Published
Abstract [en]

This work deals with the closed-loop control of streaky structures induced by free-stream turbulence (FST), at the levels of 3.0% and 3.5 %, in a zero-pressure-gradient transitional boundary layer, by means of localized sensors and actuators. A linear quadratic Gaussian regulator is considered along with a system identification technique to build reduced-order models for control. Three actuators are developed with different spatial supports, corresponding to a baseline shape with only vertical forcing, and to two other shapes obtained by different optimization procedures. A computationally efficient method is derived to obtain an actuator that aims to induce the exact structures that are inside the boundary layer, given in terms of their first spectral proper orthogonal decomposition (SPOD) mode, and an actuator that maximizes the energy of induced downstream structures. All three actuators lead to significant delays in the transition to turbulence and were shown to be robust to mild variations in the FST levels. Integrated total drag reductions observed were up to 21% and 19% for turbulence intensity levels of 3.0% and 3.5 %, respectively, depending on the considered actuator. Differences are understood in terms of the SPOD of actuation and FST-induced fields along with the causality of the control scheme when a cancellation of disturbances is considered along the wall-normal direction. The actuator optimized to generate the leading downstream SPOD mode, representing the streaks in the open-loop flow, leads to the highest transition delay, which can be understood due to its capability of closely cancelling structures in the boundary layer.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS, 2020
Keywords
boundary layer control, drag reduction, transition to turbulence
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-267150 (URN)10.1017/jfm.2019.893 (DOI)000508121500034 ()
Note

QC 20200217

Available from: 2020-02-17 Created: 2020-02-17 Last updated: 2020-02-17Bibliographically approved
Borodulin, V. I., Ivanov, A. V., Kachanov, Y. S., Mischenko, D. A., Örlü, R., Hanifi, A. & Hein, S. (2019). Experimental and theoretical study of swept-wing boundary-layer instabilities. Three-dimensional Tollmien-Schlichting instability. Physics of fluids, 31(11), Article ID 114104.
Open this publication in new window or tab >>Experimental and theoretical study of swept-wing boundary-layer instabilities. Three-dimensional Tollmien-Schlichting instability
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2019 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 31, no 11, article id 114104Article in journal (Refereed) Published
Abstract [en]

Extensive combined experimental and theoretical investigations of the linear evolution of three-dimensional (3D) Tollmien-Schlichting (TS) instability modes of 3D boundary layers developing on a swept airfoil section have been carried out. The flow under consideration is the boundary layer over an airfoil at 350 sweep and an angle of attack of +1.5 degrees. At these conditions, TS instability is found to be the predominant one. Perturbations with different frequencies and spanwise wavenumbers are generated in a controlled way using a row of elastic membranes. All experimental results are deeply processed and compared with results of calculations based on theoretical approaches. Very good quantitative agreement of all measured and calculated stability characteristics of swept-wing boundary layers is achieved.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2019
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-271311 (URN)10.1063/1.5125812 (DOI)000515320800038 ()2-s2.0-85075269350 (Scopus ID)
Note

QC 20200331

Available from: 2020-03-31 Created: 2020-03-31 Last updated: 2020-03-31Bibliographically approved
Borodulin, V. I., Ivanov, A. V., Kachanov, Y. S., Mischenko, D. A., Örlü, R., Hanifi, A. & Hein, S. (2019). Experimental and theoretical study of swept-wing boundary-layer instabilities. Unsteady crossflow instability. Physics of fluids, 31(6), Article ID 064101.
Open this publication in new window or tab >>Experimental and theoretical study of swept-wing boundary-layer instabilities. Unsteady crossflow instability
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2019 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 31, no 6, article id 064101Article in journal (Refereed) Published
Abstract [en]

Extensive combined experimental and theoretical investigations of the linear evolution of unsteady (in general) Cross-Flow (CF) and three-dimensional (3D) Tollmien-Schlichting (TS) instability modes of 3D boundary layers developing on a swept airfoil section have been carried out. CF-instability characteristics are investigated in detail at an angle of attack of -5 degrees when this kind of instability dominates in the laminar-turbulent transition process, while the 3D TS-instability characteristics are studied at an angle of attack of +1.5 degrees when this kind of instability is predominant in the transition process. All experimental results are deeply processed and compared with results of calculations based on several theoretical approaches. For the first time, very good quantitative agreement of all measured and calculated stability characteristics of swept-wing boundary layers is achieved both for unsteady CF- and 3D TS-instability modes for the case of a boundary layer developing on a real swept airfoil. The first part of the present study (this paper) is devoted to the description of the case of CF-dominated transition, while the TS-dominated case will be described in detail in a subsequent second part of this investigation.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2019
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-255496 (URN)10.1063/1.5094609 (DOI)000474440800020 ()2-s2.0-85067248795 (Scopus ID)
Note

QC 20190919

Available from: 2019-09-19 Created: 2019-09-19 Last updated: 2019-09-19Bibliographically approved
Negi, P., Hanifi, A. & Henningson, D. S. (2019). Global Stability of rigid-body-motion fluid-structure-interaction problems.
Open this publication in new window or tab >>Global Stability of rigid-body-motion fluid-structure-interaction problems
2019 (English)Report (Other academic)
Abstract [en]

A rigorous derivation and validation for linear fluid-structure-interaction (FSI) equations for a rigid-body-motion problem is performed in an Eulerian framework. We show that the “added-stiffness” terms arising in the formulation of Fanion et al. (2000) vanish at the FSI interface in a first-order approximation. Several numerical tests with rigid-body motion are performed to show the validity of the derived formulation by comparing the time evolution between the linear and non-linear equations when the base flow is perturbed by identical small-amplitude perturbations. In all cases both the growth rate and angular frequency of the instability matches within 0.1% accuracy. The derived formulation is used to investigate the phenomenon of symmetry breaking for a rotating cylinder with an attached splitter-plate. The results show that the onset of symmetry breaking can be explained by the existence of a zero-frequency linearly unstable mode of the coupled fluid-structure-interaction system. Finally, the structural sensitivity of the least stable eigenvalue is studied for an oscillating cylinder, which is found to change significantly when the fluid and structural frequencies are close to resonance.

Publisher
p. 38
Series
TRITA-SCI-RAP ; 2019:007
National Category
Fluid Mechanics and Acoustics Aerospace Engineering
Research subject
Aerospace Engineering
Identifiers
urn:nbn:se:kth:diva-262856 (URN)
Funder
Swedish National Infrastructure for Computing (SNIC)
Note

QC 20191025. QC 20191030

Available from: 2019-10-23 Created: 2019-10-23 Last updated: 2019-10-30Bibliographically approved
Quintanilha, H. J., Theofilis, V. & Hanifi, A. (2019). Global transient-growth analysis of hypersonic flow on the hifire-5 elliptic cone model. In: AIAA Scitech 2019 Forum: . Paper presented at AIAA Scitech Forum, 7-11 January 2019, San Diego, California. American Institute of Aeronautics and Astronautics Inc, AIAA
Open this publication in new window or tab >>Global transient-growth analysis of hypersonic flow on the hifire-5 elliptic cone model
2019 (English)In: AIAA Scitech 2019 Forum, American Institute of Aeronautics and Astronautics Inc, AIAA , 2019Conference paper, Published paper (Refereed)
Abstract [en]

Linear global non-modal instability analysis of the boundary layer over the Hypersonic International Flight Research Experimentation 5 (HIFiRE-5) rounded-tip 2:1 elliptic cone model is performed on a plane normal to the cone symmetry axis. The base flow has been computed using the US3D solver at Ma=7 and flight altitude of 33km and has been analyzed with respect to its modal instability in earlier work. The present objective is to interrogate the same flow regarding the existence of optimal transiently growing small-amplitude disturbances and correlate the latter with exponentially-growing modal instability mechanisms that have been confirmed to exist in this flow. Perturbation energy growth is calculated here using Singular Value Decomposition (SVD) of the linearized Navies-Stokes evolution operator: local transient growth analysis is performed by linearizing about an one-dimensional profile extracted from the base flow, while global non-modal analysis is performed by performing the SVD of the operator linearized about the full two-dimensional steady state on the plane. In both cases linear optimal perturbations are computed; local results are consistent with those of earlier analysis of the compressible flat-plate boundary layer, while global transient growth analysis results obtained herein reveal both symmetric and antisymmetric global modes emerging out of the temporal integration of the linearized operator in the limit of asymptotically large times. This scenario of emergence of modal perturbations in a non-modal analysis, in which no explicit assumption of harmonic time-dependence of linear perturbations has been made, is consistent with analogous findings in a number of incompressible flows and reconciles earlier modal and non-modal linear instability analysis results obtained on the HIFiRE-5 model configuration. � 2019 by German Aerospace Center (DLR). Published by the American Institute of Aeronautics and Astronautics, Inc.

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics Inc, AIAA, 2019
Keywords
Aerodynamics, Aviation, Hypersonic boundary layers, Hypersonic flow, Incompressible flow, Linearization, Singular value decomposition, Stability, Transient analysis, Warships, American Institute of Aeronautics and Astronautics, Flat plate boundary layers, German aerospace centers, Harmonic time dependence, International flights, Linear instability analysis, Linear perturbations, Temporal integration, Modal analysis
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-262461 (URN)10.2514/6.2019-2148 (DOI)2-s2.0-85068893493 (Scopus ID)9781624105784 (ISBN)
Conference
AIAA Scitech Forum, 7-11 January 2019, San Diego, California
Note

QC 20191018

Available from: 2019-10-18 Created: 2019-10-18 Last updated: 2019-10-18Bibliographically approved
Brynjell-Rahkola, M., Hanifi, A. & Henningson, D. S. (2019). On the stability of a Blasius boundary layer subject to localised suction. Journal of Fluid Mechanics, 871, 717-741
Open this publication in new window or tab >>On the stability of a Blasius boundary layer subject to localised suction
2019 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 871, p. 717-741Article in journal (Refereed) Published
Abstract [en]

In this study the origins of premature transition due to oversuction in boundary layers are studied. An infinite row of circular suction pipes that are mounted at right angles to a flat plate subject to a Blasius boundary layer is considered. The interaction between the flow originating from neighbouring holes is weak and for the parameters investigated, the pipe is always found to be unsteady regardless of the state of the flow in the boundary layer. A stability analysis reveals that the appearance of boundary layer transition can be associated with a linear instability in the form of two unstable eigenmodes inside the pipe that have weak tails, which extend into the boundary layer. Through an energy budget and a structural sensitivity analysis, the origin of this flow instability is traced to the structures developing inside the pipe near the pipe junction. Although the amplitudes of the modes in the boundary layer are orders of magnitude smaller than the corresponding amplitudes inside the pipe, a Koopman analysis of the data gathered from a nonlinear direct numerical simulation confirms that it is precisely these disturbances that are responsible for transition to turbulence in the boundary layer due to oversuction.

Place, publisher, year, edition, pages
CAMBRIDGE UNIV PRESS, 2019
Keywords
boundary layer stability, transition to turbulence
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-264150 (URN)10.1017/jfm.2019.326 (DOI)000493076600011 ()2-s2.0-85066907512 (Scopus ID)
Note

QC 20191209

Available from: 2019-12-09 Created: 2019-12-09 Last updated: 2019-12-09Bibliographically approved
Borodulin, V. I., Ivanov, A. V., Kachanov, Y. S., Mischenko, D. A., Örlü, R., Hanifi, A. & Hein, S. (2019). Receptivity coefficients of vortex-vibrational type at excitation of 3D Tollmien-Schlichting waves in a boundary layer on a swept wing. In: HIGH-ENERGY PROCESSES IN CONDENSED MATTER (HEPCM 2019): Proceedings of the XXVI Conference on High-Energy Processes in Condensed Matter, dedicated to the 150th anniversary of the birth of S.A. Chaplygin: . Paper presented at 26th All-Russian Conference on High Energy Processes in Condensed Matter: Dedicated to the 150th Anniversary of the Birth of S.A. Chaplygin, HEPCM 2019; Novosibirsk; Russian Federation; 3 April 2019 through 5 April 2019. American Institute of Physics (AIP), Article ID 030044.
Open this publication in new window or tab >>Receptivity coefficients of vortex-vibrational type at excitation of 3D Tollmien-Schlichting waves in a boundary layer on a swept wing
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2019 (English)In: HIGH-ENERGY PROCESSES IN CONDENSED MATTER (HEPCM 2019): Proceedings of the XXVI Conference on High-Energy Processes in Condensed Matter, dedicated to the 150th anniversary of the birth of S.A. Chaplygin, American Institute of Physics (AIP), 2019, article id 030044Conference paper, Published paper (Refereed)
Abstract [en]

The paper is devoted to the first results of an experimental quantitative study of the receptivity mechanism of a swept-wing laminar boundary layer related to scattering of 2D freestream vortices (with frequency fv) at 3D local surface vibrations (with frequency fs) resulting in an excitation of Tollmien-Schlichting (TS) waves (having combination frequencies f+ = fs+fv and f- = fs - fv). The experiments were carried out in a low-turbulence level wind tunnel on a high-precision experimental model of long-laminar-run swept airfoil (sweep angle of 35°) at a freestream speed of about 10 m/s. Controlled localized 3D surface vibrations and 2D freestream vortices were generated by special disturbance sources. Quantitative characteristics of the studied receptivity mechanism (receptivity coefficients) were estimated.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2019
Series
AIP Conference Proceedings, ISSN 0094-243X ; 2125
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-262562 (URN)10.1063/1.5117426 (DOI)2-s2.0-85070555367 (Scopus ID)9780735418653 (ISBN)
Conference
26th All-Russian Conference on High Energy Processes in Condensed Matter: Dedicated to the 150th Anniversary of the Birth of S.A. Chaplygin, HEPCM 2019; Novosibirsk; Russian Federation; 3 April 2019 through 5 April 2019
Note

QC 20191025

Available from: 2019-10-25 Created: 2019-10-25 Last updated: 2019-10-25Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-5913-5431

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