Use of digitally filtered inflow conditions for LES of flows over backward facing steps

Chakravarthy, V. Kalyana; Arora, Konark; Chakraborty, Debasis

doi:10.1016/j.euromechflu.2017.10.006

Cited by 6 publications

(5 citation statements)

References 36 publications

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“…Thus, uniform are observed in the first of the separation bubble (). The separated flow then rapidly reaches its strongest level at , which is very close to the value () reported by Chakravarthy, Arora & Chakraborty (2018). As the free shear layer reattaches on the downstream wall (), the turbulent boundary layer recovers and returns to a typical turbulent level ().…”

Section: Resultssupporting

confidence: 88%

“…As the free shear layer reattaches on the downstream wall (x/δ 0 = 8.9), the turbulent boundary layer recovers and C f returns to a typical turbulent level ( C f = 0.0027). The reattachment length L r ≈ 3.0h is in a good agreement with the previous experimental work by Bolgar et al (2018) and the numerical study by Chakravarthy et al (2018), who reported values of L r = 3.2h and L r = 3.0h, respectively. Compared with the laminar case (blue dotted lines), the mean skin friction further confirms the shorter separation length in the turbulent case.…”

Section: Mean Flow Featuressupporting

confidence: 91%

“…(2018) and the numerical study by Chakravarthy et al. (2018), who reported values of and , respectively. Compared with the laminar case (blue dotted lines), the mean skin friction further confirms the shorter separation length in the turbulent case.…”

Section: Resultsmentioning

confidence: 81%

See 2 more Smart Citations

Low-frequency unsteadiness mechanisms in shock wave/turbulent boundary layer interactions over a backward-facing step

Hickel

Oudheusden

2021

J. Fluid Mech.

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Section: Resultssupporting

confidence: 88%

Section: Mean Flow Featuressupporting

confidence: 91%

See 1 more Smart Citation

Low-frequency unsteadiness mechanisms in shock wave/turbulent boundary layer interactions over a backward-facing step

Hickel

Oudheusden

2021

J. Fluid Mech.

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show abstract

“…For the turbulent case, it can be seen that Lr/h = 2.93 is very close to the reported values, for example, Lr/h = 3.0 reported by Chakravarthy, Arora, and Chakraborty. 47 The root mean square (rms) of the wall pressure prms = √ ⟨p ′ p ′ ⟩/ρ∞u 2 ∞ is plotted in Fig. 5(b), illustrating the level of fluctuations and the generation of turbulence.…”

Section: A Comparison Of Transition Process With Different Initial Disturbance Levelsmentioning

confidence: 99%

Influence of upstream disturbances on the primary and secondary instabilities in a supersonic separated flow over a backward-facing step

Hickel

Oudheusden

2020

Physics of Fluids

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The development of primary and secondary instabilities is investigated numerically for a supersonic transitional flow over a backward-facing step at Ma = 1.7 and Re δ 0 = 13 718. Oblique Tollmien-Schlichting (T-S) waves with properties according to linear stability theory (LST) are introduced at the domain inlet with zero, low, or high amplitude (cases ZA, LA, and HA). A well-resolved large eddy simulation (LES) is carried out for the three cases to characterize the transition process from laminar to turbulent flow. The results for the HA case show a rapid transition due to the high initial disturbance level such that the non-linear interactions already occur upstream of the step, before the Kelvin-Helmholtz (K-H) instability could get involved. In contrast, cases ZA and LA share a similar transition road map in which transition occurs in the separated shear flow behind the step. Case LA is analyzed in detail based on the results from LST and LES to scrutinize the evolution of T-S, K-H, and secondary instabilities, as well as their interactions. Upstream of the step, the linear growth of the oblique T-S waves is the prevailing instability. Both T-S and K-H modes act as the primary mode within a short distance behind the step and undergo a quasilinear growth with a weak coupling. Upon pairing of the large K-H vortices, subharmonic waves are produced, and secondary instabilities begin to dominate the transition. Simultaneously, the growth of T-S waves is retarded by the slow resonance between subharmonic K-H and secondary instabilities. The vortex breakdown and reattachment downstream further contribute to the development of the turbulent boundary layer.

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“…Statnikov et al [15] study revealed that strong wall pressure fluctuations occur at Sr D ≈0.1, Sr D ≈0.2, and Sr D ≈0. 35 and are associated with the longitudinal cross-pumping motion of the separation bubble, the cross-flapping motion of the shear layer, and the swinging motion of the shear layer, respectively. Further, they identified the shape of the antisymmetric modes at Sr D =0.2, which is primarily responsible for the buffet loads on the nozzle.…”

Section: Introductionmentioning

confidence: 99%

Mach number dependence of Spectral Character of Unsteady Pressure field on Axisymmetric Backward Facing Step: Transonic Flows

Vikramaditya

Viji

2023

Preprint

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The unsteady pressure field over an axisymmetric backward-facing step was investigated experimentally at transonic Mach numbers of 1.05, 1.2, and 1.4. The study was aimed at examining the influence of transonic Mach numbers on the spatio-temporal character of the unsteady pressure field and on the dominant modes/mechanisms driving it. Surface flow visualization, Schlieren, and unsteady pressure measurements were carried out as a part of the experimental investigation. From oil flow visualization and schlieren, the reattachment region was identified, and consequently, the mean reattachment length was estimated. The mean reattachment length shows an increase with the increase in Mach number. The coefficient of mean pressure along the rearbody imitates a classical backward-facing step flow profile and can be divided into three distinct regions. The peak values of the coefficient of mean pressure and the coefficient of rms are seen to decrease with an increase in the freestream Mach number. Conventional spectral analysis reveals that as the Mach number increases, the dominant peak in the spectra shifts to lower frequencies. From the spectra, three dominant fluid dynamic mechanisms depending on the Mach number have been identified. Proper Orthogonal Decomposition (POD) analysis shows that 79–84% of the total energy contribution comes from the first six modes. The temporal dynamics of the POD modes indicate three prominent mechanisms are responsible for the unsteady pressure field. Spectral analysis of POD modes indicates that the spectra are primarily driven by the first three POD modes for M∞=1.05 and the first two modes for M∞=1.2 and 1.4. Moreover, it reveals the presence of three dominant modes, and the freestream Mach number strongly dictates the dominant mode that is driving the pressure field.

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Use of digitally filtered inflow conditions for LES of flows over backward facing steps

Cited by 6 publications

References 36 publications

Low-frequency unsteadiness mechanisms in shock wave/turbulent boundary layer interactions over a backward-facing step

Low-frequency unsteadiness mechanisms in shock wave/turbulent boundary layer interactions over a backward-facing step

Influence of upstream disturbances on the primary and secondary instabilities in a supersonic separated flow over a backward-facing step

Mach number dependence of Spectral Character of Unsteady Pressure field on Axisymmetric Backward Facing Step: Transonic Flows

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