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Author

Srisha M. V. Rao

Other affiliations: Muroran Institute of Technology
Bio: Srisha M. V. Rao is an academic researcher from Indian Institute of Science. The author has contributed to research in topics: Mach number & Supersonic speed. The author has an hindex of 10, co-authored 29 publications receiving 258 citations. Previous affiliations of Srisha M. V. Rao include Muroran Institute of Technology.

Papers
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Journal ArticleDOI
TL;DR: In this article, two supersonic nozzles Tip Ring Supersonic Nozzle and Elliptic Sharp Tipped Shallow (ESTS) Lobed Nozzle have been developed to enhance mixing at high speeds.

63 citations

Journal ArticleDOI
TL;DR: In this paper, an experimental study has been carried out on the mixing characteristics of a two-dimensional supersonic ejector with a two dimensional primary flow (air) of Mach number 2.48 and the secondary flow (subsonic) which is induced from the ambient.
Abstract: Key features that drive the operation of a supersonic ejector are the complex gasdynamic interactions of the primary and secondary flows within a variable area duct and the phenomenon of compressible turbulent mixing between them, which have to be understood at a fundamental level. An experimental study has been carried out on the mixing characteristics of a two dimensional supersonic ejector with a supersonic primary flow (air) of Mach number 2.48 and the secondary flow (subsonic) which is induced from the ambient. The non-mixed length, which is the length within the ejector for which the primary and secondary flow remain visually distinct is used to characterize the mixing in the ejector. The operating pressures, flow rates and wall static pressures along the ejector have been measured. Two flow visualization tools have been implemented—time resolved schlieren and laser scattering flow visualization. An important contribution has been the development of in-house image processing algorithms on the MATLAB platform to detect the non-mixed length from the schlieren and laser scattering images. The ratio of mass flow rates of the secondary flow to primary flow (entrainment ratio) has been varied in a range of 0.15–0.69 for two locations of the primary nozzle in the ejector duct. Representative cases have been computed using commercial CFD tool (Fluent) to supplement the experiments. Significant outcomes of the study are—the non-mixed length quantified from the flow visualization images is observed to lie within 4.5 to 5.2 times the height of the mixing duct which is confirmed by the wall static pressure profiles. The flow through the supersonic ejector in the mixed regime is explained using corroborative evidences from different diagnostic tools. A reduction of the non-mixed length by 46.7% is observed at operating conditions when the nozzle is sufficiently overexpanded. The disturbance caused to the mixing layer due to unsteady shock-boundary layer interactions within the nozzle at such conditions enhances mixing. The analysis of time resolved schlieren images have provided interesting observations on repetitive back and forth motion of the shock cells in the primary flow with a co-flowing secondary flow in the confines of the supersonic ejector. The oscillations have significant amplitudes (order of the nozzle height) at the centerline. The details of these experiments followed by the analysis of data and the inferences drawn from the results are discussed in this article.

58 citations

Journal ArticleDOI
TL;DR: In this article, a high compression ratio intake at a Mach number of M = 6 was studied in a hypersonic wind tunnel at a flight realistic Reynolds number (Re = 8.7 × 106/m).
Abstract: Understanding start–unstart behavior of intakes in hypersonic Mach numbers is essential for seamless operation of scramjet engines. We consider a high compression ratio intake (CR = 40) at a Mach number of M = 6 in this work. Start–unstart characteristics are studied in a hypersonic wind tunnel at a flight realistic Reynolds number (Re = 8.7 × 106/m, M = 6). A flap provided at the rear end of the isolator simulates the effect of backpressure for throttling ratios in the range of 0–0.69. Experiments are conducted in two modes: (a) with the flap fixed at a particular throttling ratio and (b) the flap moved to a particular throttling ratio after the started flow has been established. Unsteady pressure measurements and time-resolved Schlieren visualization are undertaken. Modal analysis of pressure (using fast Fourier transform) and Schlieren images (using dynamic mode decomposition) are carried out. The intake shows started behavior for throttling ratios up to 0.31 and a dual behavior, where it remains started in dynamic flap runs but unstarted in fixed flap runs for throttling ratios of 0.35 and 0.42. The intake exhibits a staged evolution to a large amplitude oscillatory unstart for throttling ratios of 0.55 and 0.69, with frequencies of 950 Hz and 1100 Hz, respectively. For the first time, a staged evolution (5 stages) to a subsonic spillage oscillatory unstart of a hypersonic intake is detailed using corroborative evidence from both time-resolved Schlieren and pressure measurements. A precursor to the final large amplitude oscillatory unstart is identified, and the flow mechanism for sustained oscillations is explained.

45 citations

Journal ArticleDOI
TL;DR: In this article, the effect of exposure time on modal analysis of high-speed schlieren images was investigated and it was found that exposure time of 5% of maximum exposure produces an 8% reduction in mode amplitude.

32 citations

Journal ArticleDOI
TL;DR: In this paper, the entrainment ratio (ER) of the ejector, the non-mixed length (LNM), and potential core length of the primary supersonic jet are measured to characterize mixing within the su-personic 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.

31 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, a comprehensive literature review on ejector refrigeration systems and working fluids is presented, which deeply analyzes ejector technology and behavior, refrigerant properties and their influence over ejector performance.
Abstract: The increasing need for thermal comfort has led to a rapid increase in the use of cooling systems and, consequently, electricity demand for air-conditioning systems in buildings. Heat-driven ejector refrigeration systems appear to be a promising alternative to the traditional compressor-based refrigeration technologies for energy consumption reduction. This paper presents a comprehensive literature review on ejector refrigeration systems and working fluids. It deeply analyzes ejector technology and behavior, refrigerant properties and their influence over ejector performance and all of the ejector refrigeration technologies, with a focus on past, present and future trends. The review is structured in four parts. In the first part, ejector technology is described. In the second part, a detailed description of the refrigerant properties and their influence over ejector performance is presented. In the third part, a review focused on the main jet refrigeration cycles is proposed, and the ejector refrigeration systems are reported and categorized. Finally, an overview over all ejector technologies, the relationship among the working fluids and the ejector performance, with a focus on past, present and future trends, is presented.

359 citations

Journal ArticleDOI
TL;DR: The objective of this work is to provide a literature survey on the research attempts made in the field of ejector refrigeration systems and the studies made on the ejector as a component.

202 citations

Journal ArticleDOI
TL;DR: In this paper, an integrated Lumped Parameter Model-Computational Fluid-Dynamics approach for off-design ejector performance evaluation is presented, which is based on a LPM with variable ejector component efficiencies provided by CFD simulations.

81 citations

Journal ArticleDOI
15 Jul 2020-Energy
TL;DR: In this paper, the role of the step condition on the mixing efficiency of the multi-jets within the scramjet was investigated, and the impact of step conditions on fuel mixing in region of the fuel injection was analyzed.

79 citations

Journal ArticleDOI
TL;DR: In this article, the impact of the geometry of the primary nozzles on the ejector performance in an R141b ejector refrigerator was investigated and the authors found that using a bigger nozzle throat, operated with lower generator temperature, is preferable.

73 citations