Large- and small-amplitude shock-wave oscillations over axisymmetric bodies in high-speed flow

Sasidharan, Vaisakh; Subrahmanyam, D.

doi:10.1017/jfm.2021.115

Cited by 9 publications

(9 citation statements)

References 13 publications

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“…Results from these studies show that even as flow moves into a higher dimensional geometric parameter space from the single-parameter spike-cylinder geometry, it only exhibits two distinct states of unsteadiness: pulsation and oscillation. These unsteady flow states are qualitatively the same as the pulsation and oscillation states reported in earlier literature on spike-cylinder flow and, hence, the same terminology was used by Sasidharan & Duvvuri (2021), Kumar & De (2021 a ) and Hornung et al. (2021) to refer to the two unsteady flow states.…”

Section: Introductionsupporting

confidence: 75%

“…In recent years there has been an interest in understanding the double cone/ramp flow behaviour with variation in more than one geometric parameter. Sasidharan & Duvvuri (2021) experimentally studied the double cone flow in the - parameter space with fixed at (cone-cylinder model), whereas Kumar & De (2021 a ) studied the double wedge flow through computations in the - parameter space with fixed at . Hornung, Gollan & Jacobs (2021) performed computations of the double cone flow with variation in all three geometric parameters.…”

Section: Introductionmentioning

confidence: 99%

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A model for frequency scaling of flow oscillations in high-speed double cones

Kumar,

Sasidharan,

Kumara

et al. 2024

J. Fluid Mech.

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Coherent small-amplitude unsteadiness of the shock wave and the separation region over a canonical double cone flow, termed in literature as oscillation-type unsteadiness, is experimentally studied at Mach 6. The double cone model is defined by three non-dimensional geometric parameters: fore- and aft-cone angles ( $\theta _1$ and $\theta _2$ ), and ratio of the conical slant lengths ( $\varLambda$ ). Previous studies of oscillations have been qualitative in nature, and mostly restricted to a special case of the cone model with fixed $\theta _1 = 0^\circ$ and $\theta _2 = 90^\circ$ (referred to as the spike-cylinder model), where $\varLambda$ becomes the sole governing parameter. In the present effort we investigate the self-sustained flow oscillations in the $\theta _1$ - $\varLambda$ parameter space for fixed $\theta _2 = 90^\circ$ using high-speed schlieren visualisation. The experiments reveal two distinct subtypes of oscillations, characterised by the motion (or lack thereof) of the separation point on the fore-cone surface. The global time scale associated with flow oscillation is extracted using spectral proper orthogonal decomposition. The non-dimensional frequency (Strouhal number) of oscillation is seen to exhibit distinct scaling for the two oscillation subtypes. The relationship observed between the local flow properties, instability of the shear layer, and geometric constraints on the flow suggests that an aeroacoustic feedback mechanism sustains the oscillations. Based on this understanding, a simple model with no empiricism is developed for the Strouhal number. The model predictions are found to match well with experimental measurements. The model provides helpful physical insight into the nature of the self-sustained flow oscillations over a double cone at high speeds.

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Section: Introductionsupporting

confidence: 75%

Section: Introductionmentioning

confidence: 99%

A model for frequency scaling of flow oscillations in high-speed double cones

Kumar,

Sasidharan,

Kumara

et al. 2024

J. Fluid Mech.

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“…The latter, in turn, generate down-stream going pressure and density waves that drive the fast transition. We note that unsteady bow shocks in hypersonic flow over axisymmetric cone-tipped cylindrical bodies have recently been observed [20]. Intriguingly, in that study, shock oscillations required an unsteady separation bubble and an unstable shear layer passing over the bubble.…”

Section: Boundary Layer Transition and A Near-nose 'Ring Of Fire'mentioning

confidence: 71%

Hypersonic Flow over Closed and Open Nose Missile Bodies: Raw and SVD-Enhanced Schlieren Imaging, Numerical Modeling, and Physical Analysis

Watkins¹,

Redford²,

Green³

et al. 2023

Boundary Layer Flows - Modelling, Computation, and Applications of Laminar, Turbulent Incompressible and Compressible Flows

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Understanding and mitigating against high heat loads at leading and blunt aerodynamic surfaces during hypersonic flight represents an ongoing technological challenge. Recent work has shown that the commercial software package, STAR CCM+, can provide reliable predictions of hypersonic aerothermodynamic flow and heating, under a wide range of complex, but common conditions. This chapter presents a preliminary experimental and numerical investigation of hypersonic flow over closed- and open-nose missile bodies, where the latter have been proposed as a means of reducing leading edge heat transfer. Four contributions are presented. First, a novel singular value decomposition (SVD)-based image processing technique is introduced, which significantly enhances the quality of raw schlieren images obtained in high-speed compressible flows. Second, numerically predicted hypersonic flow about a scale-model missile body, obtained using STAR-CCM+, is validated against experimental schlieren image data, an empirical correlation connecting bow shock stand-off distance and shock density ratio, and estimated drag forces. Third, scaling and physical arguments are presented as a means of choosing appropriate gas equations of state and for interpreting results of numerical simulations and experiments. Last, numerical experiments show that the forward facing cavity used in our wind tunnel experiments functions as a heat sink, reducing heat fluxes on the missile body downstream of the cavity.

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“…Experiments were performed at six different Reynolds numbers in the range 2.3 × 10 5 ≤ Re D ≤ 5 × 10 5 ; the flow conditions are summarised in table I, where P 0 and T 0 denoted the total pressure and total temperature, respectively. In all experiments high-speed schlieren data was recorded at 100,000 frames per second in the near wake flow region; the schlieren set-up is similar to the one used earlier in RNHWT [13]. The schlieren "knife-edge" was set to a horizontal position to capture density (ρ) gradients normal to the free-stream flow direction, i.e.…”

Section: Wind Tunnel Experimentsmentioning

confidence: 99%

Strouhal number universality in high-speed cylinder wake flows

Thasu¹,

Subrahmanyam²

2022

Preprint

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Flow oscillations in the near-wake region of a 2D circular cylinder are experimentally investigated at Mach 6 over the Reynolds number range 2.3 × 10 5 to 5 × 10 5 . The oscillation frequency is obtained by spectral proper orthogonal decomposition of high-speed schlieren data. The Strouhal number based on the length of the near-wake shear layers is found to exhibit universal behavior. This corroborates experimental findings at Mach 4 from recent literature, and further, the universal behavior is also seen to hold with respect to Mach number. Time-resolved pressure measurements at the flow separation points on the cylinder aft surface show that coherent oscillatory activity occurs with a phase difference of π radians between the two statistically-symmetric halves of the flow. This aspect of the flow dynamics at high speeds is in common with its low-speed counterpart, i.e. the canonical problem of cylinder wake in an incompressible flow.

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Large- and small-amplitude shock-wave oscillations over axisymmetric bodies in high-speed flow

Abstract: Abstract

Cited by 9 publications

References 13 publications

A model for frequency scaling of flow oscillations in high-speed double cones

A model for frequency scaling of flow oscillations in high-speed double cones

Hypersonic Flow over Closed and Open Nose Missile Bodies: Raw and SVD-Enhanced Schlieren Imaging, Numerical Modeling, and Physical Analysis

Strouhal number universality in high-speed cylinder wake flows

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