دانلود کتاب مروری بر نسبیت عام و زمان فضا

Ever since the Wright brothers made their successful maiden air flight, continuous technological development has been ongoing in aviation and space applications, and, as a result, we have witnessed various stages of development such as gas turbine engines with different configurations, rocket engines, and air-breathing engines. Needless to say, the power-to-weight ratio is a crucial design parameter and affects the performance of air transportation vehicles. The desire for a hypersonic flight has motivated engineers for decades to satisfy the demands for high-speed transport and economical access to space [1–6]. In order to meet these needs and ambitions, significant advancements in propulsion technology are required. It is observed that gas turbine-driven aircraft engines could achieve a speed limited to a subsonic range. Rocket propulsion technology has emerged as a solution to hypersonic range flights, but safety and low specific impulse is the Achilles heel of this innovation. Great success is achieved when the concept of a ramjet evolved, leading to the elimination of compressors and turbines. These mechanical units’ role has been replaced by the strategically constructed geometrical contour of a ramjet’s body that acts as a diffuser and an expander. Through these modifications, the ramjet could enter into a hypersonic operating range owing to reduced weight. During the operation of the ramjet while it has attained supersonic speed, the airflow rushing into the combustor is retarded with the objective to achieve the desired thermodynamic state and favourable recirculation zones conducive for accelerating the combustion process. However, studies advocate not reducing the speed of the internal airflow below Mach number 7 in order to reduce energy losses that would take place as the intensity of retardation increases, and, this, in turn, will give impetus to skin drag friction and associated surface heating problem.