Shock-related unsteadiness of axisymmetric spiked bodies in supersonic flow

Sahoo, Devabrata; Karthick, S. K.; Das, Subhajyoti; Cohen, Jacob

doi:10.1007/s00348-020-03130-2

Cited by 20 publications

(11 citation statements)

References 54 publications

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“…In Figure 14 a-b, cumulative energy contents of the ranked modes 70,71 are shown for the variations in θ and ξ . The dominant mode (k = 1) contains roughly 20% of the total energy in the fluid domain in θ variation cases (Figure 14a).…”

Section: F Spatiotemporal Modesmentioning

confidence: 99%

Unsteady dynamics in a subsonic duct flow with a bluff body

George,

Karthick,

Srikrishnan

et al. 2022

Preprint

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A series of reduced-order numerical simulations on a specific bluff body type (v-gutters) in a subsonic duct flow is done to assess the unsteady wake dynamics. Two of the v-gutter's geometrical parameters are varied: the v-gutter's base angle (θ ) and the size of a slit (ξ ) at the leading-edge of the v-gutter. Turbulent flow kinematics and pressure field are analyzed to evaluate the unsteadiness at a freestream Mach number of M ∞ = 0.25 and a freestream Reynolds number based on bluff body's transverse length (L) of Re L = 0.1 × 10 6 . Five v-gutter angles are considered (θ , • = π/6, π/4, π/3, 5π/12, π/2) and three slit sizes (ξ , mm =0,0.25,0.5) are considered only for a particular θ = [π/6]. In general, high fluctuations in velocity and pressure are seen for the bluffest body in consideration (θ = π/2) with higher drag (c d ) and total pressure loss (∆p 0 ). However, bluffer bodies produce periodic shedding structures that promote flow mixing. On the other hand, the presence of a slit on a streamlined body (θ = π/6) tends to efficiently stabilize the wake and thus, producing almost a periodic shedding structure with lower c d and ∆p 0 . For θ = [π/6], broadened spectra in vortex shedding is seen with a peak at [ f L/u ∞ ] ∼ 0.08. For θ ≥ [π/4], a dominant discrete shedding frequency is seen with a gradual spectral decay. Similarly, the effects of ξ on the θ = [π/6] case produce a discrete shedding frequency instead of a broadened one, as told before. The shedding frequency increases to a maximum of [ f L/u ∞ ] ∼ 0.26 for the maximum slit size of ξ = 0.5. From the analysis of the x − t diagram and the modal analysis of vorticity and velocity magnitude in the wake, the peaks are indeed found to agree with the spectral analysis. More insights on the shedding vortices, momentum deficit in the wake, varying energy contents in the flow field, and the dominant spatiotemporal structures are also provided.

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Section: F Spatiotemporal Modesmentioning

confidence: 99%

Unsteady dynamics in a subsonic duct flow with a bluff body

George,

Karthick,

Srikrishnan

et al. 2022

Preprint

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“…Most of them are experiments, and a few of them are computations. The plot is generated from the collective literature available on the spiked body flow physics presented in Table 1 of Sahoo et al 44 Surprisingly, from the figure, it can be seen that there are scarcely a few cases available at high M 1 and high Re D .…”

Section: Introductionmentioning

confidence: 99%

Unsteady pulsating flowfield over spiked axisymmetric forebody at hypersonic flows

et al. 2022

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The paper gives experimental observations of the hypersonic flow past an axisymmetric flat-face cylinder with a protruding sharp-tip spike. Unsteady pressure measurements and high-speed schlieren images are performed in tandem on a hypersonic Ludwieg tunnel at a freestream Mach number of M 1 ¼ 8:16 at two different freestream Reynolds numbers based on the base body diameter (Re D ¼ 0:76 Â 10 6 and 3:05 Â 10 6 ). The obtained high-speed images are subjected further to modal analysis to understand the flow dynamics parallel to the unsteady pressure measurements. The protruding spike of length to base body diameter ratio of ½l=D ¼ 1 creates a familiar form of an unsteady flowfield called "pulsation." Pressure loading and fluctuation intensity at two different Re D cases are calculated. A maximum drop of 98.24% in the pressure loading and fluctuation intensity is observed between the high and low Re D cases. Due to the low-density field at low Re D case, almost all image analyses are done with the high Re D case. Based on the analysis, a difference in the pulsation characteristics is noticed, which arises from two vortical zones, each from a system of two "k" shocks formed during the "collapse" phase ahead of the base body. The interaction of shedding vortices from the k-shocks' triple-points, along with the rotating stationary waves, contributes to the asymmetric high-pressure loading and the observation of shock pulsation on the flat-face cylinder. The vortical interactions forming the second dominant spatial mode with a temporal mode carry a dimensionless frequency (f 2 D=u 1 % 0:34) almost twice that of the fundamental frequency (f 1 D=u 1 % 0:17). The observed frequencies are invariant irrespective of the Re D cases. However, for the high-frequency range, the spectral pressure decay is observed to follow an inverse and À7/3 law for the low and high Re D cases, respectively.

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“…Many researchers have conducted numerous experimental and computational studies in order to understand flow instability arising out of spike. 16,[20][21][22][23][24][25] In open literature, the influences of spike have been experimented and computed by changing various geometric features and with different altered flow parameters. For example, the influence of spike have been studied with different L/D ratios (L is the length of the spike from the tip and D is the base body diameter), tip geometry shape of spike, positioning and inclination of spike to the base body, Mach number, Reynolds number, Angle of incidence, etc.…”

Section: Introductionmentioning

confidence: 99%

Supersonic flow investigation of a drag reducing conical spike on a hemispherically blunted nose body

Sarwar¹,

Kumar²,

Das³

2022

Proceedings of the Institution of Mechanical Engineers, Part G:

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Experiments and computations were made at a Mach number of 2.0 on a hemispherical blunt nose body with a conical spike of L/D ratio = 1.0. Attempts were made to alter the axisymmetric cavity formation between the spike tip head and the blunt base body. Qualitative measurements and quantitative details indicate the changes which support the drag reduction beyond the conventional sharp spike. Additional drops in drag values were observed by the techniques used in the present investigation. A linear trend of drag reduction is obtained with conical spikes which lead to the drag of a pure conical body.

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Shock-related unsteadiness of axisymmetric spiked bodies in supersonic flow

Cited by 20 publications

References 54 publications

Unsteady dynamics in a subsonic duct flow with a bluff body

Unsteady dynamics in a subsonic duct flow with a bluff body

Unsteady pulsating flowfield over spiked axisymmetric forebody at hypersonic flows

Supersonic flow investigation of a drag reducing conical spike on a hemispherically blunted nose body

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