The three-dimensional development of controlled transition in a flat-plate boundary layer is investigated by direct numerical simulation (DNS) using the complete Navier-Stokes equations. investigations are based on so-called spatial model, thus allowing realistic simulations spatially developing phenomena as observed laboratory experiments. For solving equations, an efficient and accurate method was developed employing fourth-order finite differences downstream wall-normal directions...

A numerical method for solving the complete Navier-Stokes equations incompressible flows is introduced that applicable investigating three-dimensional transition phenomena in a spatially growing boundary layer. Results are discussed test case with small disturbances which detailed comparison to linear stability theory possible. The validity of our model nonlinear demonstrated by realistic spatial simulations experiments Kachanov and Levchenko1 subharmonic resonance breakdown Klebanoff et...

Abstract The convective primary amplification of a forced two-dimensional perturbation initiates the formation essentially large-scale vortices in laminar separation bubble. These are then shed from bubble with forcing frequency. Immediately downstream their formation, get distorted spanwise direction and quickly disintegrate into small-scale turbulence. laminar–turbulent transition is dominated by this vortex breakup process. Using numerical experimental data, we give an in-depth...

The mechanism of turbulence development in periodic Klebanoff transition a boundary layer has been studied experimentally and direct numerical simulation (DNS) with controlled disturbance excitation. In order to compare the results quantitatively, flow parameters were matched both methods, thus providing complementary data which origin process could be explained. Good agreement was found for amplitude shape typical structures, Λ-vortices, including ring-like vortices spikes time traces....

The mutual interaction of laminar–turbulent transition and mean flow evolution is studied in a pressure-induced laminar separation bubble on flat plate. flat-plate boundary layer subjected to sufficiently strong adverse pressure gradient that develops. Upstream the small-amplitude disturbance introduced which causes transition. Downstream transition, strongly changes and, due viscous–inviscid interaction, overall distribution changed as well. As consequence, also upstream location....

A direct-numerical-simulation study of spatially evolving compressible zero-pressure-gradient turbulent boundary layers is presented for a fine-meshed range Mach numbers from 0.3 to 2.5. The use an identical set-up all subsonic and supersonic cases warrants proper comparability allows highly reliable quantitative evaluation mean-flow scaling laws the settlement on commonly accepted velocity profile in considered Reynolds number range. All data are compared literature data-base where...

Abstract Aquatic animals have developed effective strategies to reduce their body drag over a long period of time. In this work, the influence scales fish on laminar-to-turbulent transition in boundary layer is investigated. Arrays biomimetic typical overlapping arrangements are placed flat plate low-turbulence laminar water channel. Transition turbulence triggered by controlled excitation Tollmien–Schlichting (TS) wave. It was found that TS wave can be attenuated with which generate...

Methods for data reconstruction and spatial enhancement of experimental a transitional boundary layer with laminar separation bubble are investigated. Particularly, proper orthogonal decomposition (POD) is applied to direct numerical simulation (DNS) extract the DNS-based POD modes, which projected onto (via least-squares procedure) in order obtain model coefficients. These coefficients then used reconstruct, “interpolate,” smooth based on DNS modes. In addition, compare assess effectiveness...

This paper presents detailed investigations related to active transition control in laminar separation bubbles. The rely on direct numerical simulations based the complete Navier-Stokes equations for a flat-plate boundary layer. A bubble is created by imposing streamwise adverse pressure gradient at freestream of integration domain. Different steady and unsteady layer disturbances are then introduced disturbance strip upstream their effects studied. It shown that size separated region can be...

Steady linear three-dimensional disturbances are investigated in a two-dimensional laminar boundary layer. The layer is subject to streamwise favourable-to-adverse pressure gradient and eventually undergoes separation. separating flow corresponds the first part of pressure-induced laminar-separation bubble on flat plate. Streamwise disturbance development such studied by means direct numerical simulation, water-tunnel experiment an adjoint-based parabolic theory suited study spatial optimal...

The influence of forward-facing steps on the amplification disturbances in transonic flows is studied numerically. main goal to find a function for an additional factor that can be incorporated into method. In present study, both two-dimensional direct numerical simulation as well linear stability theory are used gain detailed information flow. Good agreement between -factor results from and obtained. Subsonic slightly supersonic show differences flow topology shape curve, but effective...

The effects of isolated, cylindrical roughness elements on laminar–turbulent transition in a flat-plate boundary layer are investigated laminar water channel. Our experiments aim at providing comparison to global linear stability theory (LST) by means hot-film anemometry and particle image velocimetry. Although the critical Reynolds number from does not match observed experiments, there distinct experimental observations indicating changeover purely convective absolute/global instability...

A laminar boundary layer separates in a region of adverse pressure gradient on flat plate and undergoes transition. The detached shear rolls up into spanwise vortices that rapidly break down small-scale turbulence. Finally, the turbulent reattaches, forming separation bubble. Development role three-dimensional disturbances for transition such bubble are studied by means direct numerical simulation with controlled disturbance input. In present case, level incoming perturbations is not...

The onset of unsteadiness in a boundary-layer flow past cylindrical roughness element is investigated for three configurations at subcritical Reynolds numbers, both experimentally and numerically. On the one hand, quasi-periodic shedding hairpin vortices observed all experiment. other global stability analyses have revealed existence varicose isolated mode, as well sinuous one, being linearly stable. Nonetheless, stable modes are highly sensitive, ascertained by pseudospectrum analysis. To...

The ine uence of two-dimensional humps and steps on the stability characteristics a laminar boundary layer is investigated by means direct numerical simulations (DNS). localized surface irregularity ishereby modeled within theCartesian grid assigning body forces oversurfacesthat need notcoincidewith lines.Comparedtotheuseofabody-e ttedcoordinatesystem,thismethodsavesmemoryandcomputationtime.The method validated ree nement tests as well comparison with water channel experiments. DNS results...

Gaining a comprehensive understanding of turbulent flows still poses one the great challenges in fluid dynamics. A well-established approach to advance this research is analysis vortex structures contained flow. In order be able perform efficiently, supporting visualization tools with clearly defined requirements are needed. paper, we present system which matches these large extent. The consists two components. first component analyzes flow by means novel combination core line detection and...

Abstract The evolution of two- and three-dimensional small-amplitude disturbances in the laminar part a separation bubble is investigated detail. We apply combination local linear stability theory, results from different experimental measurement campaigns direct numerical simulations to identify two discrete eigenmodes bubble. A stable eigenmode, outer mode, governs unsteady oscillations upstream However, this perturbation quickly overtaken by an unstable inner which eventually leads...

Abstract The linear stability of the compressible flow in a streamwise corner is studied. steady laminar mean obtained as solution to parabolized Navier–Stokes equations with asymptotic cross-flow velocity enforced on far-field boundaries via sponge region and was found be good agreement corresponding self-similar solution. eigenvalue problem theory solved for base flows at three different Mach numbers representing incompressible limit ( $\mathit{Ma}= 0. 01$ ), subsonic 95$ ) supersonic 1....

A direct numerical simulation study of self-similar compressible flat-plate turbulent boundary layers (TBLs) with pressure gradients (PGs) has been performed for inflow Mach numbers 0.5 and 2.0. All cases are computed smooth PGs both favourable adverse PG distributions (FPG, APG) thus akin to experiments using a reflected-wave set-up. The equilibrium character allows systematic comparison between sub- supersonic cases, enabling the isolation pure effects from Mach-number an investigation...