Linear and Nonlinear Flow Analysis of Elements of a Supersonic Inlet

Khobragade, Nikhil; Unnikrishnan, S.; Kumar, Rajan

doi:10.2514/1.j060591

Cited by 4 publications

(4 citation statements)

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“…An explicit approach (Shu & Osher 1988) was also utilized to ensure that the mean and unsteady features of the flow fields are not sensitive to the choice of the time-integration scheme. The DNS solver has been validated and applied to boundary layer and inlet-related problems in prior publications (Unnikrishnan & Gaitonde 2020; Khobragade, Unnikrishnan & Kumar 2021).…”

Section: Methodsmentioning

confidence: 99%

“…A preliminary analysis of the ROC reported in Khobragade et al. (2021) addresses various computational requirements for this flow, including grid resolution, inflow turbulence generation parameters and spanwise extent. The grids utilized for the current simulations have a wall-normal spacing, , over the ramp-side wall, corresponding to the finer grid adopted in the above study.…”

Section: Methodsmentioning

confidence: 99%

“…The spanwise extent of the grid is chosen to be around six times the peak spanwise integral length scale over the notched ROC, as reported in Khobragade et al. (2021). In the turbulized region of the ramp (), the DNS mesh resolution in wall units is , and .…”

Section: Methodsmentioning

confidence: 99%

“…The computational domain spans 0 ≤ x ≤ 11.8, 0 ≤ y ≤ 3.26 and −0.2 ≤ z ≤ 0.2, with the origin at the leading edge of the compression ramp. The spanwise extent of the grid is chosen to be around six times the peak spanwise integral length scale over the notched ROC, as reported in Khobragade et al (2021). In the turbulized region of the ramp (x ∼ 8.5), the DNS mesh resolution in wall units is x + ∼ 6.9, y + ∼ 0.77 and z + ∼ 4.1.…”

Section: Flow Configurations Studiedmentioning

confidence: 99%

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Flow instabilities and impact of ramp–isolator junction on shock–boundary-layer interactions in a supersonic intake

2022

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Boundary layer instabilities and shock–boundary-layer interactions (SBLIs) critically affect the performance and safe operation of mixed-compression air intakes. We present a computational study anchored in companion experiments, to evaluate the multimodal mechanisms driving the dynamics of the external compression ramp flow and the cowl SBLI in a Mach $3$ intake. Boundary layer transition over the external ramp is first analysed through a global linear analysis, and the linear estimates are further validated through direct numerical simulations. The separation bubble over the ramp harbours three-dimensional stationary instabilities that induce transition, under the influence of secondary instabilities driven by the shear layer modes of the bubble. The interaction of the resulting turbulized boundary layer with the cowl shock at the ramp–isolator junction and its control through geometrical modification constitutes the second part of the study. We tested a faceted (baseline) and a notched (modified) junction design to evaluate its impact on the low-, mid- and high-frequency scales generated at the cowl SBLI region. In relation to the baseline case, the notched geometry effectively locks the separation point of the bubble, thus attenuating the upstream low-frequency breathing motion. The notch also energizes the midfrequency content through vortex shedding in a well-developed shear layer, which persists into the isolator, thus assisting in an efficient compression process through cross-stream mixing of near-wall flow. The isolator boundary layer in the notched design exhibits relatively lower static pressures and higher velocity fluctuations, which are conducive to improving the flow stability, unstart margin and efficiency of high-speed propulsion systems.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Flow Configurations Studiedmentioning

confidence: 99%

See 2 more Smart Citations

Flow instabilities and impact of ramp–isolator junction on shock–boundary-layer interactions in a supersonic intake

2022

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Response of second-mode instability to backward-facing steps in a high-speed flow

Gong,

Tu,

Wan

et al. 2024

Physics of Fluids

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Stability in a Mach 4.5 boundary layer over backward-facing steps (BFSs) is investigated using numerical methods. Two types of cases are considered with different laminar inflow conditions, imposed with single-frequency or broadband-frequency modes, respectively. Compared with the typical K-type transition over a flat plate, the boundary layer transition initiated by 90 kHz-frequency second mode appears to follow the same pattern but with a noticeable delay over the step. A larger step height leads to a better inhibition of the downstream Λ-vortices and thus a later transition, providing the step height is smaller than the local boundary layer thickness. Moreover, both the frequency weighted power spectral density and the root mean square of the streamwise velocity indicate the presence of Kelvin–Helmholtz (K–H) instability when the step height is equivalent to the thickness of the nearby boundary layer. There may exist an optimal step height for suppressing single-frequency (90 kHz) mode without exciting significant K–H modes. Similar to the previous studies on roughness, BFS can act as an amplifier for the low-frequency second modes and a suppressor for the high-frequency second modes. The critical frequency is equal to that of the unstable mode whose synchronization point is exactly located at the step corner. Additionally, the correction effects of the step induce the change of the phase speed of the fast mode, which correspondingly results in the movement of the synchronization point. Generally, the BFS is not able to completely alleviate the transition initiated by the broadband-frequency second modes but can still delay the boundary layer transition in a certain degree by suppressing the high-frequency unstable waves.

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Effects of Nose Bluntness on Hypersonic Transition over Ogive-Cylinder Forebodies

Aswathy Nair,

Unnikrishnan

2024

AIAA Journal

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Ogive cylinders are representative designs of hypersonic forebodies and harbor several flow complexities. This work evaluates the effects of nose bluntness of ogive-cylinder forebodies on their laminar, transitional, and turbulent boundary layers (BLs). Laminar simulations indicate that the thickness of BL and entropy layer (EL) increases with nose bluntness, with the latter displaying a stronger sensitivity to nose radius due to the increased strength and curvature of the leading-edge shock system. Linear perturbation analysis identifies the presence of the second mode, the first mode, and EL modes with increasing bluntness. While the former two are prevalent over a significant streamwise extent, EL modes are limited to the upstream region, well within the swallowing length. Using direct numerical simulations, it is found that transition over the sharpest nose design occurs through the modal fundamental resonance route, driven by second-mode instabilities. Due to weakened BL modes, the blunter geometries undergo transition further downstream in the low-amplitude freestream perturbation environment tested in this study. The transition mechanism in the blunter geometries is intermittent in nature and appears to be driven by turbulent spots generated from streamwise vortices reminiscent of Klebanoff modes.

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Linear and Nonlinear Flow Analysis of Elements of a Supersonic Inlet

Cited by 4 publications

References 59 publications

Flow instabilities and impact of ramp–isolator junction on shock–boundary-layer interactions in a supersonic intake

Flow instabilities and impact of ramp–isolator junction on shock–boundary-layer interactions in a supersonic intake

Response of second-mode instability to backward-facing steps in a high-speed flow

Effects of Nose Bluntness on Hypersonic Transition over Ogive-Cylinder Forebodies

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