Reynald Bur | Onera - Academia.edu (original) (raw)

Papers by Reynald Bur

An important goal of the TFAST project was to study the effect of the location of transition in r... more An important goal of the TFAST project was to study the effect of the location of transition in relation to the shock wave on the separation size, shock structure and unsteadiness of the interaction area. Boundary layer tripping (by wire or roughness) and flow control devices (Vortex Generators and cold plasma) were used for boundary layer transition induction. As flow control devices were used here in the laminar boundary layer for the first time, their effectiveness in transition induction was an important outcome. It was intended to determine in what way the application of these techniques induces transition. These methods should have a significantly different effect on boundary layer receptivity, i.e. the transition location. Apart from an improved understanding of operation control methods, the main objective was to localize the transition as far downstream as possible while ensuring a turbulent character of interaction. The final objective, involving all the partners, was to b...

Experiments in Fluids, 2022

Transitional shockwave/boundary layer interactions (SBLI) are studied experimentally. Experiments... more Transitional shockwave/boundary layer interactions (SBLI) are studied experimentally. Experiments are conducted on a hollow-cylinder flare model in the R2Ch blowdown facility at a Mach number of 5 for three different Reynolds numbers in the transitional regime. Unsteady wall pressure measurements are conducted along with mean and unsteady heat flux measurements and high-speed Schlieren imaging. The images are then processed using Proper Orthogonal Decomposition (POD) and Spectral Proper Orthogonal Decomposition (SPOD) to extract relevant information. Two main phenomena are identified and documented: the oblique modes traveling in the shear layer above the recirculation region and the streaks appearing in the reattachment region. New results illustrating the multiple physical origins of the streaks, either linked with globally unstable modes and convectively unstable mechanisms, are discussed.

Theor. Comput. Fluid Dyn., 2021

A high-fidelity simulation of the massively separated shock/transitional boundary layer interacti... more A high-fidelity simulation of the massively separated shock/transitional boundary layer interaction caused by a 15-degrees axisymmetrical compression ramp is performed at a free stream Mach number of 6 and a transitional Reynolds number. The chosen configuration yields a strongly multiscale dynamics of the flow as the separated region oscillates at low-frequency, and high-frequency transitional instabilities are triggered by the injection of a generic noise at the inlet of the simulation. The simulation is post-processed using Proper Orthogonal Decomposition to extract the large scale low-frequency dynamics of the recirculation region. The bubble dynamics from the simulation is then compared to the results of a global linear stability analysis about the mean flow. A critical interpretation of the eigenspectrum of the linearized Navier-Stokes operator is presented. The recirculation region dynamics is found to be dominated by two coexisting modes, a quasi-steady one that expresses itself mainly in the reattachment region and that is caused by the interaction of two self-sustained instabilities, and an unsteady one linked with the separation shock-wave and the mixing layer. The unsteady mode is driven by a feedback loop in the recirculation region, which may also be relevant for other unsteady shock-motion already documented for shock-wave/turbulent boundary layer interaction. The impact of the large-scale dynamics on the transitional one is then assessed through the numerical filtering of those low wavenumber modes; they are found to have no impact on the transitional dynamics.

The present study is aimed to analyse the effect of passive vortex generators in a transonic inte... more The present study is aimed to analyse the effect of passive vortex generators in a transonic interaction between a shock-wave and a turbulent boundary layer in a channel flow at Mach number M = 1.45. Control of the boundary layer detachment downstream of the shock is obtained thanks to momentum transfer given by passive control devices, mechanical vortex generators (VG), located upstream of the shock and distributed in the spanwise direction. The channels lower wall is equipped with a contour profile - a bump - allowing flow separation. Two-component PIV velocity measurements are performed using the iterative gradient-based cross-correlation algorithm FOLKI-SPIV developed at ONERA. The evolution of the bulk flow and of the separated bubble due to the shock-wave boundary layer interaction is accurately quantified. Changes in the turbulent behaviour are also analysed thanks to the fluctuating fields. Comparisons with the already known flow without control give an appraisal of the eff...

40th Fluid Dynamics Conference and Exhibit, 2010

The purpose of the present study is to investigate two-dimensional unsteady transonic flows in a ... more The purpose of the present study is to investigate two-dimensional unsteady transonic flows in a channel with a sonic throat and a moderately strong normal shock downstream of the throat. The aim of the present work is to obtain a precise description of the unsteady flow in order to characterize the evolution of the boundary layer and the shock in space and time. Shock oscillations whose amplitudes are of about 10 times the order of the boundary layer thickness and frequencies much lower than turbulence frequencies (Strouhal number of about 3×10-4) are investigated. Two optical diagnostic methods were used. The first one is a spark light system coupled with a rotating camera. The second one is an acquisition method using a two-component laser Doppler velocimeter synchronized with a reference signal. Continuous and unsteady pressure measurements were performed.

Journal of Spacecraft and Rockets, 2001

This paper gives an extensive presentation of the accessible experimental data bank of the ONERA ... more This paper gives an extensive presentation of the accessible experimental data bank of the ONERA Fundamental/Experimental Aerodynamics Department concerning high speed flows. Sophisticated non-intrusive measurements (3-component Laser Velocimetry, Particle Image Velocimetry, Coherent Anti-Stokes Raman Scattering, Pressure Sensitive Paint), flow visualisations (Electron Beam Fluorescence, Schlieren photography, Shadowgraphy) and more classical measurements have been used to the investigation of complex aerodynamic phenomena involved in jets, nozzle and base flows, air intakes and wing profiles. These experimental data contribute to the physical analysis of high speed flow interactions and they constitute “computable” test cases with perfectly defined limit conditions on typical geometries. The presented test cases are accessible under authorisation request with the ONERA-DAFE department. The motivation of this paper is to give rise to new numerical contributions and to favour Eastern...

This paper has the objective to present an overview of recent experimental studies conducted in t... more This paper has the objective to present an overview of recent experimental studies conducted in the S3Ch transonic wind tunnel of the ONERA Meudon centre. Experimental investigations have been carried out on a civil transport aircraft power plant configuration to point out the complex wing / pylon / nacelle interference. Control of turbulent buffet phenomenon was performed on a swept wing by means of mechanical and fluidic vortex generators actuators. As a follow up study, the problem of laminar flow over wings in transonic flow conditions was tackled by an in-depth analysis of the shock dynamics in laminar conditions.

27th AIAA Aerodynamic Measurement Technology and Ground Testing Conference, 2010

This paper presents an application of the Pressure Sensitive Paint (PSP) technique to investigate... more This paper presents an application of the Pressure Sensitive Paint (PSP) technique to investigate two-dimensional unsteady flow in a transonic channel. This work takes place in the study of the transonic interaction between an oscillating shock-wave and a separated boundary layer in a channel flow. Oscillation of the shock-wave is forced thanks to a periodic variation of the downstream throat section given by a rotating elliptical shaft located near this throat inducing pressure perturbations moving upstream. The channel's lower wall is equipped with a contour profile-or a bump-allowing for flow separation. In order to achieve reduced response time, we use Anodized-Aluminum coating as PSP (AA-PSP) instead of usual paint. Thus, an aluminum insert including the bump has been manufactured in the contour profile and coated with AA-PSP. Images are acquired by using a fast frame rate camera and PSP results are compared with pressure tap and Kulite sensor measurements implemented in the insert. Spectral analysis have been carried out to assess the ability of AA-PSP for understanding unsteady aspects of the flow against unsteady pressure sensors.

Aerospace Science and Technology, 2003

... b Aerothermodynamics Branch, NASA Langley Research Center, Hampton, VA, 23681-2199, USA. ... ... more ... b Aerothermodynamics Branch, NASA Langley Research Center, Hampton, VA, 23681-2199, USA. ... [7]. BR Hollis, Experimental and computational aerothermodynamics of a Mars Entry vehicle, Ph.D., North Carolina State University, Raleigh (USA), Dec. ...

Aerospace Science and Technology, 1998

Passive control applied to a turbulent shock wave/boundary layer interaction has been investigate... more Passive control applied to a turbulent shock wave/boundary layer interaction has been investigated by considering a two-dimensional channel flow. The field resulting from application of passive control has been probed in great detail by using a two-component laser Doppler velocimetry system to execute mean velocity and turbulence measurements. Four different perforated plates have been considered, as also the solid wall reference case. The performed measurements have shown that passive control deeply modifies the inviscid flowfield structure, the unique strong shock being replaced by a lambda shock system. This fractionning of the compression induces a substantial reduction of the wave drag associated with the interaction. On the other hand, the combined injection-suction effect taking place in the control region provokes an important thickening of the boundary layer. There results an increase of the friction drag which nearly outbalances the gain in wave drag. A determination of the total drag in the control region was made. It was found that passive control induced a modest decrease of this drag compared to the solid wall case. Also, the rugosity of the holes is an important source of drag (excrescence drag) which contributes to compromise the potential benefit of the passive control technique. 0 Elsevier, Paris

Aerospace Science and Technology, 2000

AIAA Journal, 2020

Flow control of separation caused by transonic shock-wave/boundary-layer interaction (SWBLI) is i... more Flow control of separation caused by transonic shock-wave/boundary-layer interaction (SWBLI) is investigated. The control of the unsteadiness associated with SWBLI is not an objective of this paper. A SWBLI in a transonic channel is considered, and Reynolds-averaged Navier-Stokes simulations are carried out to compute the flow in the test section. The massive separation due to the interaction is controlled by fluidic vortex generators (VGs). Ten VGs are positioned in the center of the test section according to analyses based on physical considerations and literature results. A first kriging-based optimization is used to determine the most appropriate pitch and skew angles of the VGs. The optimum configuration found is then considered, and a second kriging algorithm is used to enhance the control of the corner flow by adding two VGs. The longitudinal and lateral locations and the pitch and skew angles of the two lateral VGs are optimized. The objective of these optimizations is to minimize the total pressure losses through the shock-wave/boundary-layer interaction. A configuration improving the objective function by 61% is found with slightly upstream-blowing jets. To understand this original finding, a comparison of the vorticity patterns generated by downstream-and upstream-blowing jets is therefore carried out.

Journal of Fluid Mechanics, 2021

A high-fidelity simulation of the shock/transitional boundary layer interaction caused by a 15° a... more A high-fidelity simulation of the shock/transitional boundary layer interaction caused by a 15° axisymmetrical compression ramp is performed at a free stream Mach number of 5 and a transitional Reynolds number. The inlet of the computational domain is perturbed with a white noise in order to excite convective instabilities. Coherent structures are extracted using spectral proper orthogonal decomposition (SPOD), which gives a mathematically optimal decomposition of spatio-temporally correlated structures within the flow. The mean flow is used to perform a resolvent analysis in order to study non-normal linear amplification mechanisms. The comparison between the resolvent analysis and the SPOD results provides insight on both the linear and nonlinear mechanisms at play in the flow. To carry out the analysis, the flow is separated into three main regions of interest: the attached boundary layer, the mixing layer and the reattachment region. The observed transition process is dependent on the linear amplification of oblique modes in the boundary layer over a broad range of frequencies. These modes interact nonlinearly to create elongated streamwise structures which are then amplified by a linear mechanism in the rest of the domain until they break down in the reattachment region. The early nonlinear interaction is found to be essential for the transition process.

J. Fluid Mech., 2019

A two-dimensional analysis of the resolvent spectrum of a Mach 1.6 transitional boundary layer i... more A two-dimensional analysis of the resolvent spectrum of a Mach 1.6 transitional
boundary layer impacted by an oblique shock wave is carried out. The investigation
is based on a two-dimensional mean flow obtained by a RANS model that includes
a transition criterion. The goal is to evaluate whether such a low cost RANS based
resolvent approach is capable of describing the frequencies and physics involved in
this transitional boundary layer/shock-wave interaction. Data from an experiment and
a companion large eddy simulation (LES) are utilized as reference for the validation
of the method. The flow is characterized by a laminar boundary layer upstream, a
laminar separation bubble (LSB) in the interaction region and a turbulent boundary
layer downstream. The flow exhibits low amplitude unsteadiness in the LSB and at
the reflected shock wave with three particular oscillation frequencies, qualified as
low, medium and high in reference to their range in Strouhal number, here based on
free stream velocity and LSB length (St = 0:03–0:11, 0.3–0.4 and 2–3 respectively).
Through the resolvent analysis this dynamics is found to correspond to an amplifier
behaviour of the flow. The resolvent responses match the averaged Fourier mode of
the time dependent flow field, here described by the LES, with a close agreement in
frequency and spatial distribution, thereby validating the resolvent approach. The low
frequency dynamics relates to a pseudo-resonance process that sequentially implies
the amplification in the separated shear layer of the LSB, an excitation of the shock
foot and a backward travelling density wave. As this wave hits back the separation
point the amplification in the shear layer starts again and loops. The medium and
high frequency modes relate to the periodic expansion/reduction of the bubble and to
the turbulent fluctuations at the reattachment point of the bubble, respectively.

SCIENCE ADVANCES, 2018

When a flying object becomes supersonic, a concomitant increase in drag leads to a considerable r... more When a flying object becomes supersonic, a concomitant increase in drag leads to a considerable rise in fuel consumption. We show experimentally that an embarked terawatt femtosecond laser can significantly decrease this drag. We measured a 50% transient reduction of drag on a test model placed in a supersonic wind tunnel at Mach 3. This effect was initiated by the thin hot air column created in front of the supersonic object by filamentation of the laser pulse. We also show that this technique offers possibilities for steering.

A transonic interaction between a shock wave and a turbulent boundary layer is experimentally and... more A transonic interaction between a shock wave and a turbulent boundary layer is experimentally and theoretically investigated. The configuration is a transonic channel flow over a bump, where a shock wave causes the separation of the boundary layer in the form of a recirculating bubble downstream of the shock foot. Different experimental techniques allow for the identification of the main unsteadiness features. As recognised in similar shock-wave/boundary-layer interactions, the flow field exhibits two distinct characteristic frequencies, whose origins are still controversial: a low-frequency motion which primarily affects the shock wave; and medium-frequency perturbations localised in the shear layer. A Fourier analysis of a series of Schlieren snapshots is performed to precisely characterise the structure of the perturbations at low-and medium-frequencies. Then, the Reynolds-averaged Navier–Stokes (RANS) equations closed with a Spalart–Allmaras turbulence model are solved to obtain a mean flow, which favourably compares with the experimental results. A global stability analysis based on the linearization of the full RANS equations is then performed. The eigenvalues of the Jacobian operator are all damped, indicating that the interaction dynamic cannot be explained by the existence of unstable global modes. The input/output behaviour of the flow is then analysed by performing a singular-value decomposition of the Resolvent operator; pseudo-resonances of the flow may be identified and optimal forcings/responses determined as a function of frequency. It is found that the flow strongly amplifies both medium-frequency perturbations, generating fluctuations in the mixing layer, and low-frequency perturbations, affecting the shock wave. The structure of the optimal perturbations and the preferred frequencies agree with the experimental observations.

This paper presents an application of the pressure-sensitive paint technique to investigate two-d... more This paper presents an application of the pressure-sensitive paint technique to investigate two-dimensional unsteady flow in a transonic channel. This work is a contribution to the study of the transonic interaction between an oscillating shock wave and a separated boundary layer in a channel flow. The shock-wave oscillation is forced by the periodic variation of the section of a second throat by means of a rotating elliptical shaft located in its section. The channel’s lower wall is equipped with a contour profile, or bump, allowing for flow separation. To achieve a reduced response time for surface pressure measurements, we use anodized-aluminum coating as pressure-sensitive paint instead of usual paint. An aluminum insert including the bump was manufactured and coated with anodized-aluminum pressure-sensitive paint. Images were acquired by using a high-speed camera, and pressure-sensitive paint results were compared with pressure tap and Kulite sensor measurements implemented in the insert. Spectral analysis was carried out to assess the ability of anodized-aluminum pressure-sensitive paint for understanding unsteady aspects of such a complex channel flow.

Experiments in Fluids, 2022

Theor. Comput. Fluid Dyn., 2021

40th Fluid Dynamics Conference and Exhibit, 2010

Journal of Spacecraft and Rockets, 2001

27th AIAA Aerodynamic Measurement Technology and Ground Testing Conference, 2010

Aerospace Science and Technology, 2003

Aerospace Science and Technology, 1998

Aerospace Science and Technology, 2000

AIAA Journal, 2020

Journal of Fluid Mechanics, 2021

J. Fluid Mech., 2019

SCIENCE ADVANCES, 2018

8th EUCASS, 2019

Femtosecond lasers can form long plasma filaments over distances ranging from several centimetres... more Femtosecond lasers can form long plasma filaments over distances ranging from several centimetres to several meters which can be used advantageously for high speed flow control, in particular for drag reduction. Recently the first experimental demonstration of femtosecond energy deposition in a wind tunnel has been reported. This paper completes this report by presenting a parametric analysis of the effect of the femtosecond energy deposition in the flow. In particular, the effect stagnation pressure on the flow perturbation and the drag variation is investigated. Drag measurements show that higher reductions in drag are obtained for larger stagnation pressures.

54th 3AF International Conference on Applied Aerodynamics, 2019

In this work, flow control of transonic shock wave boundary layer interactions is investigated. A... more In this work, flow control of transonic shock wave boundary layer interactions is investigated. A wind-tunnel experiment featuring the Délery bump is considered and RANS simulations are carried out to compute the flow inside the test section. The massive separation due to shock wave / boundary layer interaction is controlled by fluidic Vortex Generators (VGs). A two steps Kriging optimization of the pitch and skew angles of twelve VGs is performed. The second step consisting in a precise optimization of the control of the corner flow separation. The goal of these optimizations is to minimize the total pressure losses through the shock wave and along both the boundary layer and the corner flows.

ECCOMAS Congress, 2016

Shock-wave/boundary layer interaction plays a major role in any circumstances where the flow beco... more Shock-wave/boundary layer interaction plays a major role in any circumstances where the flow becomes supersonic, either locally or in totality. This phenomenon is not clearly understood when the transitional regime (from laminar to turbulent) of the boundary layer appears during the interaction process, which is the case for compressor or turbine cascades configurations and for laminar transport/business aircraft wing.
An experimental investigation in the S8Ch research wind tunnel of the ONERA Meudon Centre at a moderate supersonic (Mach number equal to 1.6) regime is carried out to quantify the effect of the shock-wave intensity on the boundary layer transition. The detection of the transition region is obtained by means of Schlieren visualizations, IR (Infra-red) thermography and TSP (Temperature Sensitive Paint) measurements. LES computation is performed on this configuration by using the block-structured solver elsA of ONERA. Comparisons of results are performed on two configurations, one at a moderate shock intensity and the other for a strong shock intensity leading to a massive boundary layer separation.