Streamline tracing in hypersonic flows is essential for designing a high-performance waverider and intake. Conventionally, the streamline equations are solved after obtaining the velocity field over a basic flow field from simplified flow... more
Streamline tracing in hypersonic flows is essential for designing a high-performance waverider and intake. Conventionally, the streamline equations are solved after obtaining the velocity field over a basic flow field from simplified flow differential equations or three-dimensional computational fluid dynamics. The hypersonic waverider shape is generated by repeatedly applying the streamline tracing approach along several planes. This approach is computationally expensive for iterative waverider optimization. We provide a novel strategy where an Artificial Neural Network (ANN) is trained to directly predict the streamlines without solving the differential equations. We consider the standard simple cone-derived waverider using Taylor–Maccoll equations for the conical flow field as a template for the study. First, the streamlines from the shock are solved for a wide range of cone angle and Mach number conditions resulting in an extensive database. The streamlines are parameterized by ...
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ESTS lobed nozzle is found to be efficient in supersonic jet mixing applications. In this study, the influence of a number of lobes on the aspects of mixing is probed using the 2D-PIV measurements. From the analysis of the obtained 2D... more
ESTS lobed nozzle is found to be efficient in supersonic jet mixing applications. In this study, the influence of a number of lobes on the aspects of mixing is probed using the 2D-PIV measurements. From the analysis of the obtained 2D velocity field, the kinematics of the lobed nozzle is reported for the first time experimentally. Centerline velocity decay, turbulence intensity, and mass efflux are calculated to compare the influence of a different number of lobes in the lobed nozzle. The conical nozzle is used as the base nozzle for comparison. It is observed that the three-lobed nozzle is efficient in terms of mixing and jet spread. Especially an increment of 70% in the jet spread is observed for three-lobed nozzle. The primary reason for the observed enhancement is due to the higher penetration of the lobe tip into the core flow (by 30% compared with the six-lobed nozzle) which produces larger-scale streamwise vortices than the other cases under consideration.
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A constant temperature hot-wire velocimetry (CTV) was used to evaluate the mixing characteristics of supersonic turbulent mixing layer. A hot-wire anemometer is calibrated against compressible air jet of flow Mach number 0.20 < M <... more
A constant temperature hot-wire velocimetry (CTV) was used to evaluate the mixing characteristics of supersonic turbulent mixing layer. A hot-wire anemometer is calibrated against compressible air jet of flow Mach number 0.20 < M < 0.84 and Reynolds number around the wire 24 < Re < 109. It is then applied to compressible turbulent mixing layer generated between flows with Mach numbers of 1.5 and 2.0 in a rectangular duct. It is demonstrated how much the root mean square of the fluctuations in mass flux ρURMS varies depending on the measuring point. The value of ρURMS at x = 62 mm and y = 7.5 mm is higher than that at x = 25 mm and y = 7.5 mm. It is seen that the mixing layer at x = 62 mm is thicker about 2.5 mm than that at x = 25 mm. In addition, the maximum value of ρURMS at x = 62 mm and y = 2.5 mm is higher about 30% than that at x = 25 mm and y = 2.5 mm. From these results, it is considered that the mixing at x = 62 mm is enhanced from that at the upstream location ...
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Supersonic gaseous ejector is practically a supersonic confined jet, where the primary supersonic jet flows through the confined passage and thereby entrains the secondary flow from the ambient. In this paper, the flow field of the... more
Supersonic gaseous ejector is practically a supersonic confined jet, where the primary supersonic jet flows through the confined passage and thereby entrains the secondary flow from the ambient. In this paper, the flow field of the supersonic gaseous ejector is investigated prominently using 2D-PIV measurement technique to study the mixing progression between the primary and the secondary flow at different operating conditions. A rectangular supersonic gaseous ejector (air-air) of low area ratio (AR = 3.7) is used in this study. Two separate supersonic primary flow nozzles of design, Mach number (MPD) 2.0 and 2.5, are considered in this experimentation. Differences between the supersonic free jet and the supersonic ejector or confined jet on the aspects of flow mixing are brought out clearly regarding flow kinematics. Centerline velocity decay, vorticity field, and wall static pressure distribution are used in parallel to explain the mixing progression in the ejector. Influence of t...
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Understanding the flow physics of confined supersonic jet is of primary importance in the design of the supersonic ejector [1] systems. Supersonic ejectors are reportedly used in gas dynamic lasers, wind tunnels, propulsive devices, and... more
Understanding the flow physics of confined supersonic jet is of primary importance in the design of the supersonic ejector [1] systems. Supersonic ejectors are reportedly used in gas dynamic lasers, wind tunnels, propulsive devices, and fuel cells. One important parameter of study in such device is non-mixed length [2] (NML). A schematic of the flow field observed in a supersonic ejector is shown in Fig. 1. Non-mixed length is defined as the zone where primary and secondary flows maintain distinct characteristics, visually [3]. Conventional techniques like pressure measurement have limitations in determining NML precisely due to constraints in placing the number of pressure sensors, spatially. Optical diagnostics tool like planar laser Mie scattering [4] (PLMS) helps to probe the flow better. This chapter explores the effect of primary flow Mach number (1.5, 2.0, 2.5, and 3.0) on the non-mixed length at different primary flow stagnation pressures (5–10 bar) using wall static pressur...
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Abstract Understanding the mechanism of local unstart in a mixed compression scramjet intake is vital for its stable off-design operation. In the present work, the local unstart behavior of a hypersonic scramjet intake is studied at a... more
Abstract Understanding the mechanism of local unstart in a mixed compression scramjet intake is vital for its stable off-design operation. In the present work, the local unstart behavior of a hypersonic scramjet intake is studied at a Mach number of 6, and a flight realistic Reynolds number of 8.4 × 10 6 /m using a combination of experiments in a hypersonic wind tunnel and numerical computations. To study the effect of internal contraction ratio (ICR), experiments are performed on an intake model that is equipped with an all movable cowl in two modes: (a) cowl fixed at a particular ICR, and (b) cowl moved to a particular ICR during the steady test time of the wind tunnel. The intake exhibits started flow for ICR between 1.19 and 1.37, and locally unstarted flow for ICR ≥1.45. In the dynamic cowl experiments, the impingement of the forebody shock onto the inner cowl surface forms a leading-edge separation bubble, which moves upstream and detaches the cowl shock, leading to local unstart with subsonic spillage of mass near cowl lip. A shear layer emanating from the triple point of shock interaction divides this subsonic flow and the supersonic flow at the ramp side. The frequency content of the flow is different between the fixed and the dynamic cowl cases. Local unstart observed during fixed cowl experiments reveal low amplitude self-sustained oscillations around a frequency of 2.5 kHz. The dynamic mode decomposition (DMD) and proper orthogonal decomposition (POD) of numerical density contours reveal that the shear layer impingement on the cowl surface drives the self-sustained oscillations observed during local unstart.
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Elliptic nozzle geometry is attractive for mixing enhancement of supersonic jets. However, jet dynamics, such as flapping, gives rise to high-intensity tonal sound. We experimentally manipulate the supersonic elliptic jet morphology by... more
Elliptic nozzle geometry is attractive for mixing enhancement of supersonic jets. However, jet dynamics, such as flapping, gives rise to high-intensity tonal sound. We experimentally manipulate the supersonic elliptic jet morphology by using two sharp-tipped lobes. The lobes are placed on either end of the minor axis in an elliptic nozzle. The design Mach number and the aspect ratio of the elliptic nozzle and the lobed nozzle are 2.0 and 1.65. The supersonic jet is exhausted into ambient under almost perfectly expanded conditions. Time-resolved schlieren imaging, longitudinal and cross-sectional planar laser Mie scattering imaging, planar Particle Image Velocimetry (PIV), and near-field microphone measurements are performed to assess the fluidic behavior of the two nozzles. Dynamic Mode Decomposition (DMD) and proper orthogonal decomposition analyses are carried out on the schlieren and the Mie scattering images. Mixing characteristics are extracted from the Mie scattering images th...
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Ejectors have many applications in aerospace and energy conversion technologies. An ejector is a passive device that pumps a secondary fluid by energy augmentation from a primary fluid. The performance of the ejector is primarily... more
Ejectors have many applications in aerospace and energy conversion technologies. An ejector is a passive device that pumps a secondary fluid by energy augmentation from a primary fluid. The performance of the ejector is primarily dependent on the complex gas dynamic interactions between the primary and secondary flows in a variable area duct. The maximum mass flow rate of the ejector in the critical flow regime is limited by choking of both the primary and secondary flows. This paper focuses on experimental investigations on the mixing characteristics of the ejector having an area ratio of 2 in the critical flow regime for a range of stagnation pressure ratios varying between 5.49 and 11.12 and a primary Mach number of 1.5, 2.0, and 2.5. The gas dynamic flow field is visualized using non-invasive high-speed schlieren and Mie-scattering techniques. Mie-scattering images are used to gain insight into the mixing characteristics and estimate the non-mixed length. The optical measurement...
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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.... more
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,...
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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... more
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 Scatter...
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ABSTRACT
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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... more
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 a...