S. K. Karthick

Bio: S. K. Karthick is an academic researcher from Technion – Israel Institute of Technology. The author has contributed to research in topics: Mach number & Supersonic speed. The author has an hindex of 7, co-authored 29 publications receiving 136 citations. Previous affiliations of S. K. Karthick include Indian Institute of Science & Schizophrenia Research Foundation.

On the unsteady throttling dynamics and scaling analysis in a typical hypersonic inlet–isolator flow

Abstract: The flow field in a two-dimensional three-ramp hypersonic mixed-compression inlet in a freestream Mach number of M∞ = 5 is numerically solved to understand the unsteady throttling dynamics. Throttling conditions are simulated by varying the exit area of the isolator in the form of plug insets. Different throttling ratios between 0 ≤ ζ ≤ 0.7 in steps of 0.1 are considered. No unsteadiness is observed for ζ ≤ 0.2, and severe unsteadiness is found for 0.3 ≤ ζ ≤ 0.7. The frequency of unsteadiness (f) increases rapidly with ζ. As ζ increases, the amount of reversed mass inside the isolator scales with the frequency and the exit mass flow rate. A general framework is attempted to scale the unsteady events based on the gathered knowledge from the numerical study. The inlet–isolator flow is modeled as an oscillating flow through a duct with known upstream design conditions such as the freestream Mach number (M∞) and the isolator inlet Mach number (Mi). Factors such as the mass occupied by the duct volume, the characteristic unsteady frequency, the throttling ratio, and the exit mass flow rate through the duct are used to form a non-dimensional parameter β, which scales with the upstream design parameter ξ = Mi/M∞. The scaling parameters are further exploited to formulate a semi-empirical relation using the existing experimental results at different throttling ratios from the open literature. The unsteady frequencies from the present two-dimensional numerical exercise are also shown to agree with the proposed scaling and the resulting semi-empirical relation.

Parametric experimental studies on mixing characteristics within a low area ratio rectangular supersonic gaseous ejector

Abstract: We use the rectangular gaseous supersonic ejector as a platform to study the mixing characteristics of a confined supersonic jet. The entrainment ratio (ER) of the ejector, the non-mixed length (LNM), and potential core length (LPC) of the primary supersonic jet are measures to characterize mixing within the supersonic ejector. Experiments are carried out on a low area ratio rectangular supersonic ejector with air as the working fluid in both primary and secondary flows. The design Mach number of the nozzle (MPD = 1.5–3.0) and primary flow stagnation pressure (Pop = 4.89–9.89 bars) are the parameters that are varied during experimentation. Wall static pressure measurements are carried out to understand the performance of the ejector as well as to estimate the LNM (the spatial resolution is limited by the placement of pressure transducers). Well-resolved flow images (with a spatial resolution of 50 μm/pixel and temporal resolution of 1.25 ms) obtained through Planar Laser Mie Scattering (PLMS) show the flow dynamics within the ejector with clarity. The primary flow and secondary flow are seeded separately with acetone that makes the LNM and LPC clearly visible in the flow images. These parameters are extracted from the flow images using in-house image processing routines. A significant development in this work is the definition of new scaling parameters within the ejector. LNM, non-dimensionalized with respect to the fully expanded jet height hJ, is found to be a linear function of the Mach number ratio (Mach number ratio is defined as the ratio of design Mach number (MPD) and fully expanded Mach number (MPJ) of the primary jet). This definition also provides a clear demarcation of under-expanded and over-expanded regimes of operation according to [MPD/MPJ] > 1 and [MPD/MPJ] < 1, respectively. It is observed that the ER increased in over-expanded mode (to 120%) and decreased in under-expanded mode (to 68%). Similarly, LNM decreased (to 21.8%) in over-expanded mode and increased (to 20.4%) in under-expanded mode. Lengthening of LPC by 139% and a reduction of 50% in shock cell spacing have also been observed for specific flow conditions. The details regarding experimentation, analysis, and discussions are described in this article.

On the unsteady throttling dynamics and scaling analysis in a typical hypersonic inlet-isolator flow.

Abstract: The flow field in a two-dimensional three-ramp hypersonic mixed-compression inlet in a freestream Mach number of $M_\infty=5$ is numerically solved to understand the unsteady throttling dynamics. Throttling conditions are simulated by varying the exit area of the isolator in the form of plug insets. Different throttling ratios between $0\leq \zeta \leq 0.7$ in steps of 0.1 are considered. No unsteadiness is observed for $\zeta\leq 0.2$ and severe unsteadiness is found for $0.3 \leq \zeta \leq 0.7$. The frequency of unsteadiness ($f$) increases rapidly with $\zeta$. As $\zeta$ increases, the amount of reversed mass inside the isolator scales with the frequency and the exit mass flow rate. A general framework is attempted to scale the unsteady events based on the gathered knowledge from the numerical study. The inlet-isolator flow is modeled as an oscillating flow through a duct with known upstream design conditions like the freestream Mach number ($M_\infty$) and the isolator inlet Mach number ($M_i$). Factors like the mass occupied by the duct volume, the characteristic unsteady frequency, throttling ratio, and the exit mass flow rate through the duct are used to form a non-dimensional parameter $\beta$, which scales with the upstream design parameter $\xi=M_i/M_\infty$. The scaling parameters are further exploited to formulate a semi-empirical relation using the existing experimental results at different throttling ratios from the open literature. The unsteady frequencies from the present two-dimensional numerical exercise are also shown to agree with the proposed scaling and the resulting semi-empirical relation.

Current Advances in Ejector Modeling, Experimentation and Applications for Refrigeration and Heat Pumps. Part 1: Single-Phase Ejectors

Abstract: Ejectors used in refrigeration systems as entrainment and compression components or expanders, alone or in combination with other equipment devices, have gained renewed interest from the scientific community as a means of low temperature heat recovery and more efficient energy use. This paper summarizes the main findings and trends, in the area of heat-driven ejectors and ejector-based machines, using low boiling point working fluids, which were reported in the literature for a number of promising applications. An overall view of such systems is provided by discussing the ejector physics principles, as well as a review of the main developments in ejectors over the last few years. Recent achievements on thermally activated ejectors for single-phase compressible fluids are the main focus in this part of the review. Aspects related to their design, operation, theoretical and experimental approaches employed, analysis of the complex interacting phenomena taking place within the device, and performance are highlighted. Conventional and improved ejector refrigeration cycles are discussed. Some cycles of interest employing ejectors alone or boosted combinations are presented and their potential applications are indicated.