Unsteady flow organization of compressible planar base flows

Humble, Raymond; Scarano, Fulvio; Oudheusden, B.W. van

doi:10.1063/1.2739411

Cited by 25 publications

(21 citation statements)

References 59 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is due to the presence of multiple flow-scale structures that play a role in the development of the transitional wake, which requires a large number of modes to be reconstructed. A similar 'flat' energy distribution has also been observed in the transitional boundary layer developing along a swept wing, in which cross-flow instability plays an important role (Serpieri & Kotsonis 2016) and the unsteady base flow at supersonic conditions (Humble, Scarano & van Oudheusden 2007). As the unsteadiness of the micro-ramp wake is stronger at higher Re h , the decrease of energy towards higher POD modes becomes moderate, resulting in 24 % of the total energy being captured by the first 20 eigenmodes, which is lower than 30 and 36 % at Re h = 730 and 460, respectively.…”

Section: Pod Analysismentioning

confidence: 62%

On Reynolds number dependence of micro-ramp-induced transition

Schrijer

Scarano

2018

J. Fluid Mech.

View full text Add to dashboard Cite

The variation of transitional flow features past a micro-ramp is investigated when the Reynolds number is decreased approaching the critical regime. Experiments are conducted in the incompressible flow spanning from supercritical to subcritical roughness-height-based Reynolds number (Re h = 1170, 730, 460 and 320) with tomographic particle image velocimetry. The effect of Re h on three-dimensional flow behaviour is analysed in a domain encompassing 73 ramp heights in the streamwise direction. Above the critical Re h , the primary vortex pair and induced central low-speed region in the mean flow field are active over longer range when decreasing Re h . In the instantaneous flow, at Re h < 1000, the hairpin vortices induced by Kelvin-Helmholtz (K-H) instability progress gradually from close to the micro-ramp into the region where the overall shear layer is destabilized, indicating the correlation between the K-H instability and the onset of transition. The breakdown of K-H vortices as observed at Re h = 1170, does not occur at lower Re h . Decreasing Re h , the secondary vortex structures make their first appearance significantly downstream, postponing the formation of sideward disturbances, which destabilize the local shear layer by ejection events. Two major types of eigenmodes with symmetric and asymmetric spatial distribution of velocity fluctuations in the near wake are clearly identified by proper orthogonal decomposition. The symmetric and asymmetric modes correspond to the presence of vortex shedding and a sinuous wiggling motion respectively. It is found that Re h is the key factor determining the importance of the symmetric mode. At Re h = 1170, the disturbance energy of the symmetric mode decays before the onset of transition, suggesting that it is relatively insignificant in the process. However, decreasing Re h to 730 and 460, the symmetric mode produces continuous growth of high level disturbance energy, leading to transition.

show abstract

Section: Pod Analysismentioning

confidence: 62%

On Reynolds number dependence of micro-ramp-induced transition

Schrijer

Scarano

2018

J. Fluid Mech.

View full text Add to dashboard Cite

show abstract

“…Later, van Oudheusden and Scarano 16 focussed on the axi-symmetric wake and the interaction between base flow and exhaust plume. The unsteady flow organization of supersonic 2D base flows has been studied by Humble et al, 17 where the large-scale unsteady flow organization has been highlighted via modal analysis based on proper orthogonal decomposition (POD, Berkooz et al 18 ).…”

Section: And Deck and Thorigny 5 )mentioning

confidence: 99%

Spatio-temporal and modal analysis of unsteady fluctuations in a high-subsonic base flow

2014

Self Cite

View full text Add to dashboard Cite

The high-subsonic flow over an axisymmetric backward facing step is investigated at a Mach number of 0.7, with high-speed particle image velocimetry operating at acquisition frequency up to 20 kHz to resolve the time dependent behavior of the separated flow in the longitudinal plane. The statistical flow properties such as the approaching boundary layer thickness, mean and fluctuating velocity field and shear layer growth are quantified. It is found that the shear layer growth is nearly linear up to x/D = 0.6; downstream this location, the reattachment surface influences the shear layer growth rate, causing it to decrease. The visualization of the high-speed measurements shows a quasi-cyclic behavior of the separated region characterized by a fluctuation of the flow reattachment location. The growing and shrinking of the separated region is accompanied by large-scale fluctuations that dominate the flow motions and the momentum exchange across the shear layer. The analysis of the large-scale fluctuations based on proper orthogonal decomposition (POD) of the velocity field indicates that the separated region exhibits pulsating behaviour as associated to the highest energy mode. The second and third modes are approximately in phase quadrature and can be associated to the growth of large azimuthal vortices that undulate the shear layer approaching the mean reattachment location. Conditional averaging of the data indicates that the second/third mode is associated to either the entrainment of high momentum fluid or ejection of low momentum fluid from the separated region depending on the phase. The high-speed measurements enable the spectral analysis of the velocity; the power spectral density of the POD time coefficients for the first three modes is evaluated. The first mode associated to pulsatile growth and collapse of the separated region yields a dominant frequency at StrD = 0.13 (f = 585 Hz) while the second mode features a broader frequency distribution in the range from 1 to 3 kHz (0.22 < StrD < 0.67) with a distinguishable peak at StrD = 0.4. The dynamical correlation between these two modes shows that time derivative of the first mode temporal coefficient and second mode coefficient are strongly correlated. This suggests that the entrainment of high momentum fluid into the separated region is responsible for the wake growth phenomenon.

show abstract

“…Proper Orthogonal Decomposition (POD) is an efficient statistical technique to provide an optimal basis for extracting the spatial structure of the most energetic fluctuations in the flow field in an average sense [14]. Such a method is particularly well suited for the detection and the extraction of large-scale energetic coherent flow structure present in turbulent flow [4,5,12].…”

Section: Pod Investigation Of the Flow Fieldmentioning

confidence: 99%

Experimental analysis of the pressure–velocity correlations of external unsteady flow over rocket launchers

Marié¹,

Druault²,

Lambaré³

et al. 2013

Aerospace Science and Technology

View full text Add to dashboard Cite

Based on simultaneous wall pressure and velocity measurements, the aerodynamic load of a launcher body model is investigated. Two different configurations are considered in order to study the influence of geometrical artifacts on the after-body flow and consequently on the aerodynamic load. After a brief presentation of the experimental setup used to get the unsteady wall pressure and external velocity field, a global analysis of the integrated pressure along the nozzle is presented for both configurations. It is shown that the unsteady load induced on a configuration with attachment device involves characteristic frequencies which fits the mechanical response of the structure whereas no particular behavior is observed on the configuration without attachment device. Then, a Proper Orthogonal Decomposition (POD) is successively performed from the wall pressure field and from the external velocity field highlighting the relationship between the most energetic structures of the flow and the involved phenomenon. Finally, a pressure-velocity correlation of the POD modes is presented and the most energetic structures of the velocity field are linked to the unsteady load observed on the nozzle. It is then confirmed the structural influence of the attachment device and its contribution to the unsteady loads acting on the nozzle.

show abstract

Unsteady flow organization of compressible planar base flows

Cited by 25 publications

References 59 publications

On Reynolds number dependence of micro-ramp-induced transition

On Reynolds number dependence of micro-ramp-induced transition

Spatio-temporal and modal analysis of unsteady fluctuations in a high-subsonic base flow

Experimental analysis of the pressure–velocity correlations of external unsteady flow over rocket launchers

Contact Info

Product

Resources

About