To gain insight into
chara
cteristi
c wake flow modes, whi
ch among others are responsible for asymmetri
cal loads on the engine extensions of spa
ce laun
chers at transoni
c speeds,
combined experimental and numeri
cal investigations of a turbulent wake flow are performed at
class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0997754615301801&_mathId=si49.gif&_user=111111111&_pii=S0997754615301801&_rdoc=1&_issn=09977546&md5=126983badd97574d144ebb52e56f7808" title="Click to view the MathML source">Ma∞=0.8class="mathContainer hidden">class="mathCode"> and
class="mathmlsrc">ce" class="mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0997754615301801&_mathId=si195.gif&_user=111111111&_pii=S0997754615301801&_rdoc=1&_issn=09977546&md5=8740d3dd95954a92a2a0e16e2d86fb8a">class="imgLazyJSB inlineImage" height="17" width="101" alt="View the MathML source" title="View the MathML source" src="/sd/grey_pxl.gif" data-inlimgeid="1-s2.0-S0997754615301801-si195.gif">cript>cal-align:bottom" width="101" alt="View the MathML source" title="View the MathML source" src="http://origin-ars.els-cdn.com/content/image/1-s2.0-S0997754615301801-si195.gif">cript>class="mathContainer hidden">class="mathCode">. The experiments are
condu
cted at the Bundeswehr University Muni
ch using planar PIV and wall pressure measurements, while the numeri
cal investigations are performed by the Institute of Aerodynami
cs at RWTH Aa
chen University using a zonal RANS–LES approa
ch and dynami
c mode de
composition (DMD). The analysis is done on a planar spa
ce laun
cher
configuration that
consists of a ba
ckward-fa
cing step with a long sho
ck-free forebody avoiding undesired sho
ck-boundary-layer intera
ctions upstream of the analyzed wake flow region. The investigated wake flow is
chara
cterized by a highly unsteady behavior of the shear layer shedding from the forebody and subsequently reatta
ching onto the splitter plate. The strong variation of the reatta
chment positions in the spanwise and the streamwise dire
ction leads to pronoun
ced wall pressure os
cillations and
consequently, stru
ctural loads. By means of a
classi
cal statisti
cal analysis, i.e., spatial and temporal Fourier transforms and two-point
correlations of experimental and numeri
cal data, one spatial
coherent s
cale with a spanwise wavelength of
class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0997754615301801&_mathId=si51.gif&_user=111111111&_pii=S0997754615301801&_rdoc=1&_issn=09977546&md5=7bd79660f846c4862bd49a2b4ee3320b" title="Click to view the MathML source">λz≈2hclass="mathContainer hidden">class="mathCode"> and two
chara
cteristi
c frequen
cies of
class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0997754615301801&_mathId=si10.gif&_user=111111111&_pii=S0997754615301801&_rdoc=1&_issn=09977546&md5=75b431e019dfc617d24966cd9d80eb74" title="Click to view the MathML source">Srh≈0.01class="mathContainer hidden">class="mathCode"> and
class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0997754615301801&_mathId=si12.gif&_user=111111111&_pii=S0997754615301801&_rdoc=1&_issn=09977546&md5=4025c27bda3ef70a5f8b4f9ce38d63a2" title="Click to view the MathML source">Srh≈0.07class="mathContainer hidden">class="mathCode"> have been obtained for the investigated wake flow problem. To
clarify the
coherent fluid motion dominating the dete
cted spatio-temporal behavior, a DMD algorithm is applied to the time-resolved three-dimensional streamwise velo
city field. The frequen
cies of the first two extra
cted stable sparsity DMD modes
closely
coin
cide with the
chara
cteristi
c peaks in the wall pressure spe
ctra. The analysis of the three-dimensional shape of the extra
cted DMD modes reveals that the dete
cted wake flow behavior is
caused by a pronoun
ced low-frequen
cy
cross-pumping motion of the re
cir
culation region and a high-frequen
cy
cross-flapping motion of the shear layer, respe
ctively. Both wake flow modes feature a pronoun
ced nearly-periodi
cal variation in the spanwise dire
ction with an approximate spanwise wavelength of two step heights. Thus, the extra
cted underlying wake modes
clearly explain the o
ccurren
ce of
corresponding peaks in the wall pressure spe
ctra, the periodi
cal formation of
wedge-shaped reatta
chment regions on the splitter plate, and the dete
ction of finger-like stru
ctures in the PIV experiments.