12th International Symposium on Turbulence and Shear Flow Phenomena (TSFP12)
Osaka, Japan (Online), July 19-22, 2022

TRANSITIONAL SHOCK-WAVE BOUNDARY LAYER INTERACTION OVER
A COMPRESSION RAMP

Nikhil Mahalingesh
Aix Marseille Univ, CNRS, IUSTIMarseille, Francenikhil.mahalingesh@univ-amu.fr

Sébastien Piponniau
Aix Marseille Univ, CNRS, IUSTIMarseille, France
sebastien.piponniau@univ-amu.fr

Pierre Dupont
Aix Marseille Univ, CNRS, IUSTIMarseille, France
pierre.dupont@univ-amu.fr

cies (Erengil & Dolling, 1991; Piponniau et al., 2009; Touber& Sandham, 2009) of the flow. Délery et al. (1986) reviewed
some of the early studies on the topic, while Dolling (2001)
provided some perspectives for future research. Clemens &Narayanaswamy (2014) recently provided a detailed retrospection of the prevailing debate on the origins of the low frequency unsteadiness. Comprehensive reviews on the subject
include books by Smits & Dussauge (2006), Doerffer et al.
(2010) and Babinsky & Harvey (2011).
However, limitations from an experimental and computational point of view had restricted much of the focus on turbulent interactions. And hence, attention to the interaction
between shock-waves and laminar boundary layers had been
relatively lower. Recent advancements in experimental techniques and computational resources, together with emerging
focus on sustainability and increased efficiency (Commission
et al., 2011), have renewed interest on laminar interactions.
As part of the European TFAST project, experiments were
performed to study such interactions at the IUSTI laboratoryof Aix-Marseille University, involving an oblique shock-wave
impinging on a laminar boundary layer. The results showeda relatively long length of interaction with large aspect ratios
compared to turbulent interactions (Diop et al., 2017). Further, temporal measurements revealed several frequencies being amplified along the interaction, with the low frequency
unsteadiness of the separation region being much higher thanthat of turbulent interactions (Diop et al., 2016). Several open
questions were left unanswered, including the specific effectsof transitional mechanisms on the spatial and temporal scalesof the interaction (Diop et al., 2019).
The current work is an extension of those experiments,
being performed with a compression ramp geometry as opposed to an oblique shock reflection case. The paper discusses the interaction between a laminar boundary layer anda 6◦ compression ramp at Mach 1.66. Reynolds number isvaried by a factor of two to investigate its effect on the interaction. The experimental setup and methodology are detailed
in the following section, describing the Pitot probe, hot-wireanemometry and Schlieren imaging. The initial part of the results focuses on the validation of the laminar boundary layer
and canonical nature of the ramp SBLI. The latter part highlights the differences in length and time scales between the

ABSTRACT
Experiments are performed to study the interaction between shock-waves and a laminar boundary layer on a compression ramp at Mach 1.66. Pitot probe measurements andhot-wire anemometry are complemented with Schlieren visualisation, while Reynolds number is varied by a factor of
two. The results suggest a “fully laminar” type of interaction
where transition of the boundary layer occurs downstream ofreattachment. On the contrary, oblique shock-wave laminarboundary layer interactions resulted in a “transitional” typeof interaction with transition occurring at reattachment, forsimilar freestream conditions and equivalent shock strength.
This difference in the type of interaction resulted in subtle deviations in the relative length and time scales of the shockwave boundary layer interaction. The non-dimensional lengths
of interactions, based on mass balance across the interaction,
were similar for the two geometrical configurations, but theevolution of these length scales with increasing Reynolds number were found to be different. The Strouhal number associated with low frequency unsteadiness matched across both theconfigurations, with typical time scales associated with transitional mechanisms in oblique shock reflection, “delayed” inthe compression ramp measurements.

INTRODUCTION
The interaction between shock-waves and boundary layers (SBLI) is a classical flow phenomenon in the field of aerodynamics. It is found in a number of real-world applications
such as transonic aerofoils, rocket nozzles, supersonic inlets,
high-speed engines, etc. and is usually characterised by a number of unfavourable effects including separation of the boundary layer, intense thermal loading, structural fatigue, leading
to unsteadiness of the associated shock-waves. Consequently,
SBLIs have been a subject of research since the 1940s (Ackeret et al., 1947). Experiments and numerical simulations havebeen performed for various geometrical configurations (suchas oblique shock impingement, compression ramps, aerofoils,
compressor and/or turbine blades, etc.) and for various flow
parameters, including different Mach and Reynolds numbers.
These studies have shed light on the spatial scales (Dupont
et al., 2006; Souverein et al., 2013) and characteristic frequen-1

12th International Symposium on Turbulence and Shear Flow Phenomena (TSFP12)
Osaka, Japan (Online), July 19-22, 2022
Pitot probe and hot-wire measurements are made in thevertical plane containing the streamwise and wall-normal directions, at the mid-span of the wind tunnel. The supersonic
Pitot probe has a flat tip of 0.15 mm in height and is used
for measurements of the laminar boundary layer profile, witha spatial resolution of 0.05 mm in the wall-normal direction.
Longitudinal explorations are also made with the Pitot probe
outside the boundary layer at a height of 5 mm from the wallwith a spatial resolution of 1 mm in the streamwise direction.
External measurements of mass-flux fluctuations are also
made using hot-wire anemometry with a tungsten and platinum wire of 2.5 µm diameter. The Streamline amplifier byDantec Dynamics is used in symmetrical bridge configuration,
operating in constant temperature mode with an overheat ratioof 0.8. The effective frequency bandwidth of the anemometer is approximately 150 kHz (depending on the unit Reynolds
number). The calibration of the anemometer is not performed
and hence the resulting spectral data are analysed in arbitrary
units of the measured voltage. Temporal acquisition is obtained using National Instruments system (NI6133) at a sampling frequency of 400 kHz for 10 seconds, resulting in four
million points of acquisition.
Flow visualisation is carried out with a conical Schlieren
setup with a low-speed acquisition system. A classical fullframe digital SLR camera (Nikon D700) is used, having a
CMOS sensor with a pixel size of 8.45 µm and a maximum
resolution of 4256 × 2832 pixels with a exposure time of 150µs.

compression ramp and oblique SBLI. These differences are
addressed in the discussion section and conclusions are drawn.

EXPERIMENTAL METHODOLOGY
The experiments are conducted in the supersonic windtunnel of IUSTI laboratory of Aix-Marseille University. It
is a closed-loop hypo-turbulent facility which can be continuously operated up to four hours without significant changes
in freestream properties. The freestream Mach number is 1.66
for a test-section of 170 mm in spanwise width and a heightof 105 mm. The compression ramp consists of an initial flat
section with a sharp leading edge and a 6◦ deflection at 115
mm from the leading edge. This geometry is placed at a heightof 25 mm from the floor of the wind tunnel as shown in Figure1.

(a) Schematic of Geometry.

RESULTS

Reattachment
Shock
LE
Shock

Mach Wave

Corner(b) Picture of Geometry.

Figure 2: Schlieren visualisation at Rec = 0.65 × 106 .

Figure 1: Compression Ramp.

Figure 2 shows the Schlieren image for the lowest
Reynolds number. A weak shock-wave from the leading edgeof the ramp (annotated by LE Shock) can be seen. A weak
Mach wave is seen originating from the roof of the wind tunnel upstream of the leading edge. This Mach wave is due toa microscopic structural discontinuity between the end of thediverging section of the nozzle and the start of the test section. Looking closely near the corner, it can be seen that theboundary layer separates a few millimetres upstream of thecorner and consequently re-attaches downstream of the corner.
A separation bubble is visible between the points of separation
and reattachment (identified by the small bright white region).
Separation of the boundary layer is not characterised by a distinct shock-wave, but rather weak compression waves whichcannot be seen by Schlieren imaging. However diffuse compression waves are observed at reattachment, which coalesce
further away from the wall and merge in to a shock-wave.
Measurements of the laminar boundary layer are madeover a simple flat plate using the Pitot probe. The geometry

Experiments are repeated for different freestream totalpressures, corresponding to different unit Reynolds numbers.
Table 1 describes the equivalent unit Reynolds number (Reu )and the Reynolds number based on the location of the corner(Rec ) for different freestream total pressures (P0 ).

Table 1: Operating conditions of the experiments.

P0 [atm]
Reu m−1 × 106

Rec × 106

0.4

5.61

0.65

0.6

8.37

0.96

0.8

11.01

1.27



2

12th International Symposium on Turbulence and Shear Flow Phenomena (TSFP12)
Osaka, Japan (Online), July 19-22, 2022
1.2

s
2c f
p − p0= F(X ∗ )(1/2)q0
M2 − 1

1

u/u e

0.8

Standard values of the coefficient of free-interaction fromvarious studies of laminar SBLIs (Babinsky & Harvey, 2011)at separation and plateau are also plotted in Figure 4. The
streamwise coordinates are normalised with respect to the location of the corner (X ∗ = 1) and the mean location of boundary layer separation (X ∗ = 0). The mean location of separation
is determined by identifying the inflection point in the gradientof pressure measurements. The measurements show a classical two-step pressure rise characteristic of separated SBLIs forthe three Reynolds numbers. The values predicted by freeinteraction theory at separation and over the plateau region are
well reproduced by the experiments, validating the canonicalnature of the measurements.

0.6
6

Rex (

0.4

10 )

0.65
0.96
1.27
Blasius BL

0.2
0
0

0.2

0.4

0.6

0.8

1

1.2

1.4

(1)

1.6

y/ 99

Figure 3: Boundary layer velocity profiles for various

streamwise locations and comparison with Blasius profile.

and setup of the flat plate is identical to the compression ramp,
and is used mainly to study the supersonic laminar boundary
layer. As the geometry is placed at a height from the floor of
the wind tunnel, a new natural laminar boundary layer develops from the leading edge. These measurements are repeated
for the same three Reynolds numbers of the compression ramp
and are shown in similarity coordinates (Figure 3). The boundary layer has a distinct linear section and having a thickness ofless than 1 mm. The measurements collapse on top of eachother and agree well with the Blasius boundary layer profile(the compressible Blasius boundary layer equations are solved
numerically to obtain the theoretical results). These measurements confirm the laminar nature of the boundary layer for thethree Reynolds numbers for the flat plate. The nature of theboundary layer is expected to be same over the compression
ramp given the similarity of two geometrical setups.

180
Oblique Shock Reflection (Diop, 2017)
Compression Ramp

140

100

60

20
0.55

0.75

0.95

1.15

1.35

Rec (x 106 )Figure 5: Variation of non-dimensional length of interaction for the three Reynolds numbers.

6
5
4

F

3

Rec (

10 6)

Additionally, Pitot measurements provide quantitative insight into the upstream influence of the SBLI through thelength of interaction, which is defined as the streamwise distance between the compression corner and the mean locationof boundary layer separation. Figure 5 shows the evolutionof this non-dimensional length of interaction (L) (normalisedwith the compressible displacement thickness of the boundary
layer at the point of separation) for the three Reynolds numbers. It seems that the non-dimensional length of interaction isnearly constant for the three Reynolds numbers. Furthermore,
Figure 5 compares the lengths of interaction to the oblique
shock reflection of Diop (2017) for a flow deflection of 3◦ . The
inviscid location of the impingement shock-wave is used as thelength scale for the Reynolds number for the oblique SBLI results. The lengths of interaction in the compression ramp cases
are lower by 47% on average, compared to the oblique shockreflection cases.
Souverein et al. (2013) proposed a scaling model for thelength scales of shock-wave boundary layer interactions taking into account the effect of different geometrical configurations. This non-dimensional length scale is defined according to Equation 2, where δ ∗ is the compressible displacement
thickness at separation, β is the inviscid shock-wave angle andϕ is the imposed flow deflection.

0.65
0.96
1.27
Plateau
Separation

2
1
0
-1
-2

-1

0

1

2

3

X*

Figure 4: Free interaction theory.

Longitudinal measurements using the Pitot probe in theexternal flow are plotted in terms of the free-interaction coefficient (Chapman et al., 1958) in Figure 4. The coefficient of
free-interaction (F(X ∗ )) is determined according to Equation
1, which takes into account the change in Reynolds number
through the skin-friction coefficient.

3

12th International Symposium on Turbulence and Shear Flow Phenomena (TSFP12)
Osaka, Japan (Online), July 19-22, 2022
Schlieren imaging. Generally, the hot-wire anemometer is sensitive to fluctuations of total temperature, mass-flux and Mach
number of the flow. In the potential region of the flow (23mm from the wall), where the Mach number is greater than
1.4 and for a high overheat of 0.8, voltage fluctuations of the
anemometer can be directly related to mass-flux fluctuations
through the King’s law coefficient (Morkovin, 1956; Dupont,
1990). The longitudinal evolution of the non-dimensionalroot-mean square (RMS) of these fluctuations are shown in
Figure 7 for the three Reynolds numbers. The streamwise coordinates are normalised similar to Figure 4.
The first point measured upstream of the interaction is anindication of the freestream noise of the wind tunnel and isaround 0.3% of the freestream mass-flux. This low value ensures that the noise is not too high to trigger bypass transitionof the laminar boundary layer (Van Ingen, 2008). An overshoot of RMS can be observed before separation (X ∗ ≈ −0.35)
and is due to the Mach wave observed from the Schlieren visualisation (Figure 2). This Mach wave is considered to be quite
weak as it has no significant effect on the mean flow (Figure4) and the RMS returns to its original value after crossing thiswave.
It can be seen that the shape of the curves are similar forthe three Reynolds numbers, suggesting that the type of interaction is similar. A clear local overshoot of RMS can be seenaround separation and reattachment, with the RMS gradually
returning to its original value after both events. No exponential
increase of RMS is observed after reattachment for the three
Reynolds numbers.

15
Oblique Shock Reflection (Diop, 2017)
Compression Ramp

L*

10

5

0
0.55

0.75

0.95

1.15

1.35

Rec (x 106 )Figure 6: Scaling of length of interaction using Souverein
et al. (2013) model.

L∗ = Lsin (β ) sin (ϕ)
sin (β − ϕ)


=

L
δ∗



sin (β ) sin (ϕ)
sin (β − ϕ)(2)

The variation of this length scale (L∗ ) for the three
Reynolds numbers is shown in Figure 6. It can be seen that thescaling significantly reduces the difference in lengths between
the two geometrical configurations, with the mean difference
being 12%.
Additionally, it is of interest to note that while the lengthscales are nearly constant for the compression ramp configuration, the same cannot be said for the oblique SBLI. Figures
5 and 6 show that the length of interaction is decreasing withincreasing Reynolds numbers. This difference is addressed in
the discussion section, after presenting the temporal results.

0.4

Normalised f * PSD

101
Rec (

Rec (

0.35

10 6)

10 6)
0.65
0.96
1.27

0.3
0.25
0.2
0.15
0.1
0.05

0.65
0.96
1.27

0
10-3

10-2

10-1

100

St L

100

Figure 8: Pre-multiplied power spectral density at reat-tachment shock-wave for the three Reynolds numbers.

10-1
-0.5

0

0.5

1

1.5

Looking at the spectral space for the three Reynolds numbers, Figure 8 shows the estimates of the power spectral density measured at the reattachment shock-wave in the external flow. The spectral data is represented in normalised premultiplied form to highlight the contribution of different frequency bands to the total energy content. Frequency is shownin the classical non-dimensional form of Strouhal number
based on the length of interaction and the freestream velocity. Probe vibrations and support oscillations are magnified
at the reattachment shock-wave, characterised by sharp localisation of energy at very low frequency and their harmonics(StL < 10−2 ). The shape of the spectra is similar for the three
Reynolds numbers with two major time scales. A low frequency scale around 0.07 ≤ StL ≤ 0.09 and a high frequency

2

X*

Figure 7: Longitudinal evolution of non-dimensionalroot-mean square of mass-flux for the three Reynolds
numbers.

Moving to the time scales of the SBLI, hot-wire anemometry gives insight into the temporal aspects of the flow. External longitudinal measurements are made over the interaction
at 23 mm from the wall. This height is chosen such that theinteraction of the probe with the SBLI is minimal, verified by4

12th International Symposium on Turbulence and Shear Flow Phenomena (TSFP12)
Osaka, Japan (Online), July 19-22, 2022
scale around 0.5 ≤ StL ≤ 0.7, which are more clearly visible atlower Reynolds numbers.

Figure 10: Longitudinal evolution of normalised pre-multiplied power spectral density at Rec = 0.65 × 106
from oblique SBLI (Diop, 2017).
Figure 9: Longitudinal evolution of normalised pre-multiplied power spectral density at Rec = 1.27 × 106
for the compression ramp.

DISCUSSION
The experiments of the oblique SBLI from Diop (2017)
showed that transitional mechanisms were strongly amplified
over the interaction, evidenced by exponential amplificationof characteristic frequency scales associated with the mixing
layer. Particularly, intermediate frequency scales (StL ≈ 0.5)
were significantly amplified over the separation bubble. These
scales were typically associated with the non-linear phase of
the transition process (Mayer et al., 2011). This led to transition of the laminar boundary layer at reattachment, featuredby the concentration of energy at high frequencies near this region. On the contrary, there is no clear evidence of transitionat reattachment in the current experiments of the compression
ramp (Figures 7 and 9), even though the freestream conditions
and the equivalent shock strength is the same. Correspondingly, the intermediate scales, thought to be essential for transition, are found after reattachment. Therefore, it seems that thetransition to turbulence occurs at some point far downstreamof reattachment. Of course, the boundary layer after reattachment is definitely altered and might not follow the shape ofa canonical Blasius profile, but it is not fully turbulent either.
This suggests that the compression ramp has a “fully laminar”
interaction as opposed to a “transitional” type for the oblique
SBLI.
This fundamental difference in the type of interaction has
subtle effects on the length and time scales between the twogeometrical configurations. It is known that the length scalesof the compression ramp are relatively smaller compared to
oblique SBLIs, due to the geometrical constraints imposed by
the ramp on the reattachment of the boundary layer, as highlighted in Figure 5 . While scaling the length scales basedon the respective geometrical configurations significantly reduces the large differences (Figure 6), a non-trivial differenceis still observed in the slope of the curves between the two geometrical configurations. For a fully laminar interaction, astransition occurs far downstream of reattachment, the lengthof interaction is thought to be governed solely from a massbalance point of view (Souverein et al., 2013). For a transitional interaction, the length scale is governed by a combination of mass balance and transitional mechanisms, which tend
to reduce the length of interaction when Reynolds number isincreased. The presence of these transitional mechanisms canbe characterised by the dominance of intermediate frequency
scales, which can be found over the separation bubble in the

To understand the evolution of dominant frequency scales
over the interaction, Figure 9 shows the contours of the normalised pre-multiplied power spectral density for the highest
Reynolds number. The Mach wave observed in Figure 7 ishighlighted by the dashed white line. Probe vibrations andtheir harmonics observed in Figure 8 can be identified here
through sharp red spots at very low frequencies at the reattachment shock-wave. The overall organisation is similar forthe three Reynolds numbers and hence the results for only one
case is shown here.
It can be seen that most of the energy is concentrated athigh frequencies before separation (notwithstanding the Machwave). Separation of the boundary layer is associated with thesame low frequency observed in Figure 8 (0.07 ≤ StL ≤ 0.09,
annotated by the black circle). On the contrary, the region
over the separation bubble is associated with high frequency
scales centred around StL ≈ 1. Low frequencies are again
found at the reattachment shock-wave of the boundary layer.
However, further downstream, intermediate frequency scales
around 0.1 ≤ StL ≤ 0.2 are most dominant. The high frequency
scales observed over the separation bubble are also found after
reattachment, although not the dominant scales.
Figure 10 is a similar visualisation of the power spectral density from the hot-wire measurements of Diop (2017)
for the interaction between an oblique shock-wave and a laminar boundary layer. These experiments were performed at thesame Mach number for a effective flow deflection of 3.7◦ andReynolds number of 0.65 million. The very low frequency
content (StL < 10−2 ) around separation (X ∗ = 0) corresponds
to an artefact of the experiment, possibly due to probe vibrations and support oscillations.
Comparison with Figure 9 shows that similar frequencies are involved at separation and over the mixing layer, with
StL ≈ 0.09 (annotated by the black circle at the bottom left)
and StL ≈ 1.5 respectively. The major difference is the concentration of most of the energy at high frequencies after reattachment (annotated by the black circle at the top right). This is associated with breakdown of coherent structures in the boundary layer leading to transition to full turbulence (Diop et al.,2019).

5

12th International Symposium on Turbulence and Shear Flow Phenomena (TSFP12)
Osaka, Japan (Online), July 19-22, 2022
2011 Flightpath 2050 : Europe’s vision for aviation : maintaining global leadership and serving society’s needs. Publications Office.
Délery, Jean, Marvin, John G & Reshotko, Eli 1986 Shockwave boundary layer interactions. Tech. Rep.. Advisory
Group for Aerospace Research and Development NeuillySur-Seine (France).
Diop, Moussa 2017 Transition à la turbulence en écoulements
compressibles décollés. PhD thesis, thèse de doctorat
dirigée par Dupont, Pierre et Piponniau, SébastienMécanique et physique des fluides. Mécanique énergétique
Aix-Marseille 2017.
Diop, Moussa, Piponniau, Sébastien & Dupont, Pierre 2017
Transition mechanism in a shock wave boundary layer interaction. In Tenth International Symposium on Turbulenceand Shear Flow Phenomena. Begel House Inc.
Diop, Moussa, Piponniau, Sébastien & Dupont, Pierre 2019
High resolution lda measurements in transitional oblique
shock wave boundary layer interaction. Experiments in Fluids 60 (4), 1–15.
Diop, Moussa, Piponniau, Sébastien & Pierre, Dupont 2016
On the length and time scales of a laminar shock wave
boundary layer interaction. In 54th AIAA Aerospace Sciences Meeting, p. 0073.
Doerffer, Piotr, Hirsch, Charles, Dussauge, Jean-Paul, Babinsky, Holger & Barakos, George N 2010 Unsteady effects ofshock wave induced separation, , vol. 114. Springer Science& Business Media.
Dolling, David S 2001 Fifty years of shock-wave/boundarylayer interaction research: what next? AIAA journal 39 (8),1517–1531.
Dupont, Pierre 1990 Etude expérimentale des champs turbulents dans une couche limite supersonique fortement
chauffée. PhD thesis, Aix-Marseille 2.
Dupont, P, Haddad, C & Debieve, JF 2006 Space and timeorganization in a shock-induced separated boundary layer.
Journal of fluid Mechanics 559, 255–277.
Erengil, Mehmet E & Dolling, David S 1991 Unsteady wave
structure near separation in a mach 5 compression rampinteraction. AIAA journal 29 (5), 728–735.
Mayer, Christian SJ, Von Terzi, Dominic A & Fasel, Hermann F 2011 Direct numerical simulation of complete transition to turbulence via oblique breakdown at mach 3. Journal of Fluid Mechanics 674, 5–42.
Morkovin, Mark V 1956 Fluctuations and hot-wire anemometry in compressible flows. North Atlantic Treaty Organization advisory Group for aeronautical research . . . .
Piponniau, Sébastien, Dussauge, Jean-Paul, Debieve, JeanFrançois & Dupont, Pierre 2009 A simple model for lowfrequency unsteadiness in shock-induced separation. Journal of Fluid Mechanics 629, 87–108.
Smits, Alexander J & Dussauge, Jean-Paul 2006 Turbulent
shear layers in supersonic flow. Springer Science & Business Media.
Souverein, LJ, Bakker, PG & Dupont, P 2013 A scaling analysis for turbulent shock-wave/boundary-layer interactions.
Journal of Fluid Mechanics 714, 505–535.
Touber, Emile & Sandham, Neil D 2009 Large-eddy simulation of low-frequency unsteadiness in a turbulent shockinduced separation bubble. Theoretical and Computational
Fluid Dynamics 23 (2), 79–107.
Van Ingen, J 2008 The en method for transition prediction.
historical review of work at tu delft. In 38th Fluid Dynamics
Conference and Exhibit, p. 3830.

oblique SBLI experiments and after reattachment for the compression ramp. Perhaps, the length scales of the compression
ramp might show the same behaviour at higher Reynolds numbers, where transition could occur at reattachment. But this isoutside the feasibility of the current experiments and hence
could not be explored.
With regard to the time scales, the low-frequency unsteadiness associated with separation are mostly similar between the two configurations, even though the type of interaction is different. This suggests that the intermediate frequency
scales do not play a significant role in the mechanisms of thelow-frequency unsteadiness. The other part of the picture is
the amplitude of unsteadiness, as Chapman et al. (1958) suggested that fully laminar interactions are “steady” in nature
while transitional interactions are unsteady. Further investigations are necessary to understand this effect in more detail.
These results highlight the delicate effects of transitional
mechanisms on the type of interaction, and consequently affecting the associated length and time scales.

CONCLUSIONSThe effect of Reynolds number on the interaction between
a laminar boundary layer and shock-waves are investigatedexperimentally over a compression ramp. Pitot probe, hotwire anemometry and Schlieren visualisation are performed
for three Reynolds numbers, varying by a factor of two between the extreme cases. The results suggest that the interaction is of the “fully laminar” type, with transition occurring far
downstream of reattachment. This is in contrast to what was
found in experiments of oblique SBLIs for the same freestream
conditions and shock strength, where transition occurred atreattachment. Further comparisons with oblique shock reflection cases show reduced lengths of interaction for the compression ramp and different evolutions of the length scale withincreasing Reynolds numbers. However, low-frequency unsteadiness associated with separation are mostly identical forboth configurations.

This work is part of the European TEAMAero project(Towards Effective Flow Control and Mitigation of Shock Effects in Aeronautical Applications). The authors would like toacknowledge the support from the European Union’s Horizon
2020 research and innovation programme under grant agreement No. EC grant 860909.

REFERENCES
Ackeret, Jakob, Feldmann, F & Rott, N 1947 Investigations ofcompression shocks and boundary layers in gases moving
at high speed. Tech. Rep..
Babinsky, Holger & Harvey, John K 2011 Shock waveboundary-layer interactions, , vol. 32. Cambridge University Press.
Chapman, Dean R, Kuehn, Donald M & Larson, Howard K
1958 Investigation of separated flows in supersonic and subsonic streams with emphasis on the effect of transition.
Clemens, Noel T & Narayanaswamy, Venkateswaran 2014
Low-frequency unsteadiness of shock wave/turbulent
boundary layer interactions. Annual Review of Fluid Mechanics 46, 469–492.
Commission, European, for Mobility, Directorate-General,
Transport, for Research, Directorate-General & Innovation

6