Editing Compressible flow (section)

==History==
The study of gas dynamics is often associated with the flight of modern high-speed aircraft and atmospheric reentry of space-exploration vehicles; however, its origins lie with simpler machines. At the beginning of the 19th century, investigation into the behaviour of fired bullets led to improvement in the accuracy and capabilities of guns and artillery.<ref name="Text">{{cite web |title=Fundamentals of Compressible Fluid Mechanics |author=Genick Bar–Meir |date=May 21, 2007 |publisher=[[ibiblio]] (Potto Project) |url=http://www.ibiblio.org/potto/text.pdf |access-date=January 23, 2020}}></ref> As the century progressed, inventors such as [[Gustaf de Laval]] advanced the field, while researchers such as [[Ernst Mach]] sought to understand the physical phenomena involved through experimentation.

At the beginning of the 20th century, the focus of gas dynamics research shifted to what would eventually become the aerospace industry. [[Ludwig Prandtl]] and his students proposed important concepts ranging from the [[boundary layer]] to supersonic [[shock wave]]s, [[supersonic wind tunnel]]s, and supersonic nozzle design.<ref name = "Text"/> [[Theodore von Kármán]], a student of Prandtl, continued to improve the understanding of supersonic flow. Other notable figures ([[Theodor Meyer|Meyer]], {{interlanguage link|Luigi Crocco|it}}, and [[Ascher H. Shapiro|Ascher Shapiro]]) also contributed significantly to the principles considered fundamental to the study of modern gas dynamics.  Many others also contributed to this field.

Accompanying the improved conceptual understanding of gas dynamics in the early 20th century was a public misconception that there existed a barrier to the attainable speed of aircraft, commonly referred to as the "[[sound barrier]]." In truth, the barrier to supersonic flight was merely a technological one, although it was a stubborn barrier to overcome. Amongst other factors, conventional aerofoils saw a dramatic increase in drag coefficient when the flow approached the speed of sound. Overcoming the larger drag proved difficult with contemporary designs, thus the perception of a sound barrier. However, aircraft design progressed sufficiently to produce the [[Bell X-1]]. Piloted by [[Chuck Yeager]], the X-1 officially achieved supersonic speed in October 1947.<ref>{{cite web|url=https://history.nasa.gov/SP-4219/Chapter3.html|title=Research in Supersonic Flight and the Breaking of the Sound Barrier|first=John D. Jr.|last=Anderson|website=history.nasa.gov|access-date=14 April 2018|archive-url=https://web.archive.org/web/20171225232732/https://history.nasa.gov/SP-4219/Chapter3.html|archive-date=25 December 2017|url-status=dead}}</ref> 

Historically, two parallel paths of research have been followed in order to further gas dynamics knowledge. Experimental gas dynamics undertakes wind tunnel model experiments and experiments in [[shock tube]]s and ballistic ranges with the use of optical techniques to document the findings. Theoretical gas dynamics considers the equations of motion applied to a variable-density gas, and their solutions.  Much of basic gas dynamics is analytical, but in the modern era [[Computational fluid dynamics]] applies computing power to solve the otherwise-intractable nonlinear partial differential equations of compressible flow for specific geometries and flow characteristics.