“Fluctuating-enthalpy source mechanisms of first- and second-mode oscillations in a hypersonic boundary layer”
Publication Type:
Conference
Authors:
Co-Authors:
D. Gaitonde
Year Published:
2019
Abstract:
Instability modes in hypersonic boundary layers (HBL) are often identified through their phase speeds. Here, we adopt a technique to quantify the physical components in various instability modes in an HBL, namely vortical, acoustic and thermal, which we designate fluid-thermodynamic (FT) components. A linear stability analysis is first performed to identify a candidate wave which exhibits first- and second-mode instabilities that are of interest in the current base flow. This wave is then excited in a forced direct numerical simulation (DNS), and the corresponding linear, harmonic solution is obtained. The DNS perturbation field is then subjected to FT splitting using the generalized approach of momentum potential theory (MPT). Results indicate that the first- and second-mode, both contain significant contribution from all the three FT components. Vortical component is the dominant form of perturbations in both the modes, with peak values appearing along the generalized inflection point. The acoustic component is significantly higher within the second-mode, compared to other locations in the HBL. Further, the source mechanisms responsible for the production of fluctuating energy in the amplification zones of the first- and second-mode are identified. While the primary source of fluctuating energy in the first-mode is vortical in nature, this term dissipates energy when the second-mode instability dominates. On the other hand, the thermal source emerges as the prime mechanism of energy production in the most potent second-mode, emphasizing its significance in high-speed flows.
Conference Name:
AIAA Science and Technology Forum and Exposition 2019
Conference Location:
San Diego, California
Other Numbers:
Refereed Designation:
Date Published:
1/6/2019