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An Experimental Investigation of Single Jet Heat Transfer with Surrounding Microjets
Title
An Experimental Investigation of Single Jet Heat Transfer with Surrounding Microjets
Creator
Ma, Weicong
Date
2019
Description
An experimental investigation of a single main jet with surrounding microjets impinging on a flat heated surface was performed to understand...
Show moreAn experimental investigation of a single main jet with surrounding microjets impinging on a flat heated surface was performed to understand the role of the higher-speed microjets on the surface heat transfer. Eight microjets 45-degrees apart were fabricated on a circular disk mounted at the exit of the main jet axisymmetric. Heat transfer enhancement on the flat surface was evaluated by comparison with the results of a baseline single round jet with the same flow rate. The average Nusselt Number and the local Nusselt number in the radial direction are reported as functions of dimensionless nozzle-to-plate distance, dimensionless radial distance, and dimensionless mass flow rate ratio. Local Nusselt number contours are plotted as a function of radial position. The area-averaged Nusselt number and local Nusselt number beyond the near-field impingement jet region increases monotonically with increasing mass flow rate ratio and decreasing of nozzle-to-target distance. The local Nusselt number at the stagnation region shows a more complex behavior with the mass flow rate ratio and nozzle-to-target distance.
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Critical Aspect Ratio And Flow Development In A Low Reynolds Number Variable Aspect Ratio Duct Utilizing Oil Film Interferometry
Title
Critical Aspect Ratio And Flow Development In A Low Reynolds Number Variable Aspect Ratio Duct Utilizing Oil Film Interferometry
Creator
Chiu, Daniel P.
Date
2019
Description
Within the realm of fluid mechanics, there has always been an interest of bridging the gap between ideal- and real fluid flows. Pertaining to...
Show moreWithin the realm of fluid mechanics, there has always been an interest of bridging the gap between ideal- and real fluid flows. Pertaining to the study of turbulent duct flow, an aspect ratio (AR) configuration that would behave in such a manner would be considered a critical aspect ratio. This would mean the flow core would be unaffected by any sidewall contributions. Such analysis is done through wall shear measurement techniques; this study used oil-film interferometry (OFI).The first steps of this study were to determine sufficient criteria to ensure that the data collected were representative of the tested configuration, e.g. parameter choice and flow development length. Previous studies used the bulk velocity U_b which is derived from the entirety of the flow. This study focuses on the flow core, thus the choice to use the center-line velocity U_C seemed appropriate. The development length pertains to testing downstream from the inlet such that parameters are independent in th`e streamwise direction. This study demonstrates that the previously held value of x/H = 100 is insufficient and that nearly twice that is required.Furthermore, this study shows three very important findings: the flow development length required for testing is x/H ≈ 200, the size of the test platform plays little part in the overall behavior of the flow, and that the critical aspect ratio is AR = 24. These findings correspond to an aspect ratio range of 12.8 ≤ AR ≤ 48 and a Reynolds number range of 0.5 × 10^4 < Re_H < 4.0 × 10^4 . From these data, the estimated relationship between the coefficient of friction and the Reynolds number is shown with the following relation:Cf,C = 0.05164 Re_H ^ −0.25
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Inviscid Shock Propagation within a Variable-Geometry Scramjet Inlet
Title
Inviscid Shock Propagation within a Variable-Geometry Scramjet Inlet
Creator
Grybko, Maciej
Date
2021
Description
The study concerns the propagation of shockwaves within an inlet of a scramjet engine and effect of inlet geometry variation on performance. A...
Show moreThe study concerns the propagation of shockwaves within an inlet of a scramjet engine and effect of inlet geometry variation on performance. A Python code was developed to simulate and visualize a flowfield within a scramjet inlet, based on inviscid oblique shock theory. The program was validated against NASA Shock software, and the results differed only by round-off error (0.05%). Subsequently a geometric sensitivity study was conducted, showing that throughout acceleration from Mach 5 to Mach 20 parameters like inlet height could be varied to ensure constant number of shocks within an inlet (preventing discontinuous changes of flowfield), whereas lower wedge angle could control compression required for optimal combustion. Correspondingly, a trajectory was determined with a constraint on static pressure entering combustion chamber (100 kPa). For an arbitrary baseline inlet geometry, it was established that beyond Mach 10 the scramjet would exceed structural load limit, despite delivering sufficient conditions for rapid combustion. Nevertheless, below Mach 10 it would operate efficiently, proving that hydrocarbon-fueled scramjets can have a fixed geometry. For higher speeds, a variable geometry is a necessity.
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REDUCED-ORDER MODELING OF UNSTEADY FLOW OVER TWO COLLINEAR PLATES AT LOW REYNOLDS NUMBERS
Title
REDUCED-ORDER MODELING OF UNSTEADY FLOW OVER TWO COLLINEAR PLATES AT LOW REYNOLDS NUMBERS
Creator
Almashjary, Abdulrahman N
Date
2021
Description
Wakes of bluff bodies that exhibit unsteady behavior are a topic of great interest in the study of fluid dynamics. Vortex formation in these...
Show moreWakes of bluff bodies that exhibit unsteady behavior are a topic of great interest in the study of fluid dynamics. Vortex formation in these wakes depends significantly on the Reynolds number and the arrangement of the bluff bodies in the computation domain. To attain a comprehensive understanding of the unsteady wakes of adjacent bodies, we examine the emerged flow patterns in the wake of two bodies when subjected to different flow regimes and geometric configurations. This work aims to develop a reduced-order model that can capture the dynamics and predict the time evolution of specific parameters in the flowfield. Investigations including direct numerical simulations of two collinear plates normal to the flow were performed. Flowfield data and forces exerted on the plates were collected using a numerical code of an immersed boundary projection method (IBPM). The conducted numerical simulations pursued classifying the flow patterns by systematically varying the Reynolds number and the gap between the two plates. It was found that at small gap spacings, a typical von Karman vortex street is observed. Whereas at larger gap spacings, both a biased and a flip-flopping gap flow are detected. Prevalent coherent structures present in various flow regimes can be extracted via data-driven modeling techniques. The proper orthogonal decomposition (POD) method is used in this framework, from which projection-based reduced-order models are developed utilizing the governing equations of fluid flows. Single and broadband spectra are observed in the unsteady wake of the two-plate configuration. The amplitude and frequency of the time-evolution of the true POD modes and the predicted models are assessed using the spectral proper orthogonal decomposition (SPOD), an empirical method to extract coherent structures one frequency at a time from fluid flows. It was found that these reduced-order models are able to recover the frequency content from non-time resolved data.
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