Numerical study of trailing and leading vortex dynamics in a forced jet with coflow

Bhatia, Beena; De, Ashoke

doi:10.1016/j.compfluid.2019.02.001

Cited by 11 publications

(7 citation statements)

References 61 publications

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“…The effect of trailing jet on the fully formed vortex ring is not significant as the flow expands like a subsonic jet (Lumley 1967). similar to incompressible vortex ring (Widnall & Sullivan 1973, Bhatia & De 2019. The Biot-Savart interaction of primary and shear layer vortex rings results in increase in diameter and decrease in velocity of the primary (can also be seen in figure 9a and 12b for t* > 4).…”

Section: Resultsmentioning

confidence: 58%

Characteristics of shock tube generated compressible vortex rings at very high shock Mach numbers

et al. 2021

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Compressible vortex rings, usually formed at the open end of a shock tube, often show interesting phenomena during their formation, evolution, and propagation depending on the shock Mach number (Ms) and exit flow conditions. The Mach number of the translating compressible vortex rings (Mv) investigated so far in the literature is subsonic as, the shock tube pressure ratio (PR) considered is relatively low. In this numerical study we focus on low to high vortex ring Mach numbers (0.31 < Mv < 1.08) cases with a particular focus on very high Mv cases that are not been reported in experiments as, it is difficult to obtain in laboratory. Using hydrogen as a driver section gas inside the shock tube, a supersonic compressible vortex ring (Mv > 1) is obtained for first time.It is established that the SST k-ω based DES turbulent model replicates the experimental observation better than the previously published results at different stages of development of the vortex ring. DES, which is an inbuilt hybrid of LES and RANS approaches is evoked that can automatically switch to the sub-grid scale (SGS) model in the LES regions (i.e. with different scale vortical structures) and to a RANS model in the rest of the region (i.e. where the grid spacing is greater than the turbulent length scale). The DES model can predict characteristics of the shear layer vortices as well as counter-rotating vortex rings (CRVRs) as reported in the experimental measurements. Formation of multiple triple points and the corresponding slip-stream shear layers and thus multipleCRVRs behind the primary vortex ring at different radial locations, in addition to the usual CRVRs, appears to be a unique characteristic for high Mach number vortex rings. For high PR, H2, case during formation stage, a vortex layer of reverse circulation (that of primary vortex ring) is formed from the outer wall of the shock tube, whose instability formed another series of opposite circulation vortices which interfere with the primary vortex ring considerably. Also, near the central zone, a near stationary slipstream vortex and multiple, fast moving tiny vortices of opposite circulation to slipstream vortex are observed. Mechanisms for formation of these complex vortex structures are identified. The implications of these phenomena on vortex rings' geometric and kinematic characteristics such as ring diameter, core diameter, circulation, translational velocity as well as vortex Mach number are discussed in detail illustrating their differences with low PR cases.

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Section: Resultsmentioning

confidence: 58%

Characteristics of shock tube generated compressible vortex rings at very high shock Mach numbers

et al. 2021

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“…Using a reconstruction based on a low number of modes containing a significant part of the variance ('energy'), a low dimensional representation of the system is obtained, often providing a way to understand critical transport phenomena in the original flow. The detailed methodology is specified in the earlier works [59][60][61][62][63][64][65][66][67] .…”

Section: F Proper Orthogonal Decomposition (Pod)mentioning

confidence: 99%

“…The choice of field variable for POD depends on the type of study, flow field, and application. Unlike an incompressible flow, analysis of a compressible or reacting flow should include a thermodynamic quantity such as temperature in addition to the velocity vector field 62 . For autoigniting flames, ignition kernels may be studied using HO2, a species playing an important role in the ignition as used in Ref.…”

Section: F Proper Orthogonal Decomposition (Pod)mentioning

confidence: 99%

Numerical analysis of dilute methanol spray flames in vitiated coflow using extended flamelet generated manifold model

Bhatia

Roekaerts

et al. 2022

Physics of Fluids

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The present work focuses on the large eddy simulation (LES) and the study of turbulent dilute methanol spray flames in vitiated coflow using the secondary-oxidizer Flamelet Generated Model (FGM). The modified FGM model uses an additional secondary oxidizer parameter in addition to the three other parameters previously used for spray flames - progress variable, mixture fraction, and enthalpy. The results for gas phase and droplet properties are validated against the dilute methanol spray flame database for varying fuel injection amounts. The droplet statistics and the lift-off flame heights are accurately captured for all the cases. A proper orthogonal decomposition (POD) of the scalar fluctuating hydroxyl radical (OH) field and velocity-temperature field capture the flame structures in the downstream region of ignition kernels. The detailed POD analysis reveals that the base frequency of the dominant OH field equals that of the dominant vortical structure of 67.3 Hz. The flame propagation happens around these dominant vortical structures because of the less-strained fluid mixing.

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“…Kosambi 45 first proposed this and later extended it by other researchers like Lumley 46 and Sirovich 47 . Previous works of the present group extensively used this technique for different flow configurations [48][49][50][51][52][53][54][55][56] . Noticeably, POD, being a powerful tool to identify spatial coherence, can not capture the phase information and miss out on the dynamic information embedded inside the system.…”

Section: Introductionmentioning

confidence: 99%

“…This means the POD eigen modes are unable to resolve the small perturbation leading to instability. Later, Schmid 53 introduced a technique based on the Koopman analysis called Dynamic Mode Decomposition (DMD), capable of extracting the dynamic information of the system. The primary difference between POD and DMD lies in orthogonalization in space and time, respectively, where each DMD mode is organized based on the observed frequencies.…”

Section: Introductionmentioning

confidence: 99%

Numerical study of trailing and leading vortex dynamics in a forced jet with coflow

Cited by 11 publications

References 61 publications

Characteristics of shock tube generated compressible vortex rings at very high shock Mach numbers

Characteristics of shock tube generated compressible vortex rings at very high shock Mach numbers

Numerical analysis of dilute methanol spray flames in vitiated coflow using extended flamelet generated manifold model

Suppression of vortex shedding using a slit through the circular cylinder at low Reynolds number

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