Supersonic boundary-layer response to optically generated
J. D. Schmisseur, S. P. Schneider, S. H. Collicott
Abstract Controlled, localized disturbances were intro-
duced into the supersonic freestream upstream of a 4:1
elliptic cross-section cone. The response of the initially
laminar boundary layer to the laser-generated freestream
perturbation was measured above the cone minor axis.
The experiment was conducted in the Mach-4 Purdue
Quiet-ﬂow Ludwieg tube at a freestream unit Reynolds
number of 4.5 million/m. The focused beam from a fre-
quency-doubled Nd:YAG laser was used to generate the
disturbance. The perturbation existed in the ﬂowﬁeld as a
region of locally heated air, referred to here as the thermal
spot. Constant-temperature anemometry was used to
characterize the boundary-layer response to the intro-
duction of the thermal spot. The response was largest and
most complex near the boundary-layer edge. The duration
of the measured boundary-layer response was an order of
magnitude greater than the measured duration of the
disturbance in the freestream. Within the boundary layer,
the mass-ﬂux deviation introduced by the thermal spot
was of the same magnitude as the local mean mass ﬂux.
The optically generated disturbance is potentially useful as
a perturbation source in future boundary-layer receptivity
The design of more efﬁcient hypersonic vehicles requires
accurate methods for predicting the transition from lam-
inar to turbulent ﬂow in high-speed boundary layers.
Knowledge of the physics of transition is essential for the
development of adequate prediction tools. Unfortunately,
few elements of the high-speed transition process are well
understood. In the past, most research focused on the
growth of boundary-layer instabilities that trigger transi-
tion. However, accurate calibrated data still remain to be
obtained, even for a round cone at zero angle of attack
(Schneider 2001). Recently, increasing emphasis has been
placed on characterizing the introduction of instabilities
by external disturbances. Disturbances enter the boundary
layer from both external and surface sources (Bushnell
1990; Reshotko 1994). External sources include acoustic
waves, particles, and freestream variations in vorticity and
entropy, while surface sources include roughness and
tripping mechanisms. Receptivity describes the propaga-
tion of external disturbances in the boundary layer, and
the resulting initiation of instabilities.
Theoretical understanding of high-speed receptivity is
in its infancy (Choudhari and Street 1993; Duck et al.
1997). Study of the critical nose region, which always has
ﬁnite bluntness, is only beginning (Zhong 1998). Very few
experimental investigations of supersonic receptivity
phenomena have been made to date. Kendall (1994) in-
vestigated the effect of both freestream turbulence and
acoustic waves on the growth of instabilities on ﬂat plates
and circular cones. Semionov et al. (1996) examined the
effect of vortical and acoustic disturbances impinging on
the leading edge of a ﬂat plate.
The processing of disturbances by shock waves has
been studied for many years, usually in the context of
incoming turbulent boundary layers (Barre et al. 1996).
Hussaini and Erlebacher (1999) have examined the inter-
action between a plane shock and a localized entropy spot,
and show that this generates a vortex ring; however, the
geometry is too different to make quantitative compari-
sons with the present measurements. To the author’s
knowledge, none of these studies has been carried out
under conditions similar to those described here.
This paper documents the application of an optically
generated, localized, freestream perturbation to the mea-
surement of disturbances in a supersonic boundary layer.
The perturbation was introduced upstream of an elliptic
cross-section cone, and the resulting response of the cone
boundary layer to the disturbance was measured. The
present effort is distinguished by the use of a single lo-
calized freestream disturbance, as opposed to the use of a
disturbance ﬁeld (Kendall 1994; Semionov et al. 1996).
Additionally, to the authors’ knowledge, this is the ﬁrst
attempt to examine boundary-layer receptivity in a
Experiments in Fluids 33 (2002) 225–232 Ó Springer-Verlag 2002
Received: 15 February 2000 / Accepted: 16 October 2001
J. D. Schmisseur (&)
Air Force Ofﬁce of Scientiﬁc Research
AFOSR/NA 801 N Randolph St Rm 732
Arlington VA 22203-1977, USA
S. P. Schneider, S. H. Collicott
W. Lafayette, IN 47907, USA
This paper is a work of the US Government and is not subject
to copyright protection in the United States.
This work was funded by the Air Force Ofﬁce of Scientiﬁc
Research under contracts monitored by Dr. Len Sakell and
Dr. Steven Walker. Additional funding for the facility was
provided by gifts from the Boeing Company and in memory of