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We argue that the fundamental assertion underlying Mach's critique of Newton's first law is that inertial motion is not motion in the absence of causes; rather, it is motion whose cause lies in some homogeneous aspect of the environment. We distinguish this formal requirement (Mach's principle) from two hypotheses which Mach considers concerning the origin of inertia: that the distant stars play (1) a merely "collateral" or (2) a "fundamental" role in the causal determination of inertial motion. In his later writings, Mach deliberately avoids referring to the concept of causation, and indeed, this has made the interpretation of Mach's principle a subject of widespread controversy. However, in his earlier writings, the substance of Mach's critique is less ambiguously expressed. Therefore, close attention is given to Mach's early writings and the evolution of his thought. Various accounts in the secondary literature on Mach's principle, in particular those of Norton and DiSalle, are assessed on this basis. We end with a defence of the Machian status and legitimacy of the early Einstein's research program. [ABSTRACT FROM AUTHOR]

Proponents of a recent interpretation of Ernst Mach's views on thought experiments argue that for Mach thought experiments must be continuous with and return to cached experiences. These criteria, the proponents hold, explain the tension which has been noted in Mach's views on thought experiments: on the one hand, Mach reprimands Newton in "extending principles beyond the boundaries of experience" when critiquing Newton's bucket argument, while on the other, Mach himself engages in speculative reasoning when presenting 'Mach's principle'. Against this interpretation, I argue that Mach's critique of Newton's argument does not turn on Newton's illegitimate use of thought experiments, but instead turns on Newton's illegitimate use of thoughts in thought experiments. Recognizing this leads to a simple and more compelling interpretation of Mach's views. I close the paper by gesturing towards such an interpretation and noting that taking Mach's views on thought experiments seriously implies that Mach is much less of a strict empiricist than he is usually understood to be. [ABSTRACT FROM AUTHOR]

The efficient injection of fuel in the combustion chamber is significant for the advancement of the current supersonic vehicles. This study has focused on the role of non-alignment injector configuration on the fuel mixing of the hydrogen jet inside the combustion chamber of the scramjet engine. The fuel distribution and vortex generation behind both annular and coaxial jets are modeled and compared to disclose the mechanism of fuel diffusion in the combustion chamber. A three-dimensional model of two nozzle angles is produced to visualize the complicated flow interaction of four non-aligned circular jets at supersonic cross-flow. Our results indicate that the strength of the vortex pair produced by the core of the fuel jet is extended more when the angle of the nozzles is increased. The flow visualization of the jet also confirms that the flow becomes more complex in non-alignment jet configurations and fuel mixing is improved by the addition of the internal air jet in the suggested injection model. • The role of non-aligned injector system for efficient fuel mixing of hydrogen jets is investigated. • CFD is used to investigate the flow and fuel mixing inside the combustor of scramjet engine. • Role of the vortex pairs on the fuel mixing and penetration is presented. [ABSTRACT FROM AUTHOR]

Mach's views on the nature of time have been unduly neglected. They are both more defensible in their own historical context and more relevant to our own contemporary context than has been appreciated. This essay provides an extended and comprehensive discussion of Mach's writings on time offering novel analysis and interpretation. Contra the prevailing current in the secondary literature, Mach's views on time are shown to be largely vindicated in the context of late nineteenth century physics. Then, building upon this more historical project, we conclude with a critical evaluation of the modern Machian view of time due to Barbour within the context of relativistic chronometry as instantiated via pulsar clocks and atomic clocks. Once more, considered analysis serves to support the Machian view. About time we go back to Mach. [ABSTRACT FROM AUTHOR]

The enhancement of fuel distribution within the combustion chamber significantly affects the productivity of scramjet engine. In current effort, comprehensive efforts have been performed to investigate the impact of the upstream ramp on the diffusion and mixing of four hydrogen multi-jets at Ma>1. Current study employed CFD to model compressible flow of air and fuel in presence of an upstream ramp with two slopes of 20 and 30. The purpose of current study is to examine fuel jet and air stream interaction when an angled divergent ramp is located nearby injectors. The three-dimensional feature of the jet in these two configurations are fully investigated and mixing performance and jet circulations are compared to reveal important factors on fuel penetration in the combustion chamber. Our findings showed that presence of an upstream ramp sufficiently improves the fuel mixing downstream of injectors. The mixing performance analysis also shows that increasing the ramp slope to 30° could increase fuel mixing around 80% far downstream. [ABSTRACT FROM AUTHOR]

Experimental analysis of base pressure in suddenly expanded compressible flow from nozzles at different Mach numbers is performed. Intensive experimentation is carried out to investigate the base pressure and wall pressure of flow expanding from the nozzles into the enlarged duct. Microjets to actively control the flow are adopted to increase the base pressure. Experiments were conducted for Mach numbers (one sonic and rest supersonic) from 1 to 3, nozzle pressure ratio (NPR) from 3 to 11. The duct length considered from 10 to 1, and the area ratios tested were from 2.56 to 6.25 are the variables whose effect on base and wall pressure is studied using response surface methodology. The K-means algorithm performs a clustering analysis of this enormous data, which provides useful information and patterns. Regression of both the pressures using a random forest classification algorithm is carried out. The response surface analysis reveals that microjets are efficient when the flow is under the influence of a favorable pressure gradient. The base pressure reduces from maximum to minimum when the flow regime changes from over to correct expansion by increasing the NPR. Lower area ratio and higher duct length have a minimum effect on base pressure. The wall pressure flow field is unaffected due to the presence of the microjets. K-means clustering revealed that a high percentage of base pressure is in the lower range. This necessitates the importance of increasing the base pressure to reduce the base drag. Random forest algorithm has proved to be a handy tool for predicting base pressure and wall pressure and similar highly non-linear data. [ABSTRACT FROM AUTHOR]