Systematic Study of Flow Through Convergent Micro-nozzle of Nanosatellite at Very Low Ambient Pressure condition
Nanosatellites are the new generation of small satellites having mass not more than 10 Kg and equipped with miniaturised propulsion system which provides necessary thrust. Nanosatellites need extremely low levels of thrust (<100 μN) for minor adjustments of orbit and precise station-keeping. Instead of launching one bulky satellite into earth’s orbit, several nanosatellites can be launched at a time into their respective orbits. These nanosatellites can work better in coordination with each other by sending the real time data of the whole globe at the same time unlike one bulky satellite which can only map a part of the globe. Micro-nozzle as a part of propulsion system has been studied, designed and improved intensively during the past few decades. It has proved to be very challenging for the researchers to design a micro-nozzle with efficiency at par with macro nozzles owing to different set of problems which are not present in macro nozzles. Some of them are viscous boundary layer formation as Reynolds number of flow becomes very low, non validity of continuum hypothesis as Knudsen number becomes greater than 0.01, heat transfer effects as surface area to volume ratio decreases with non-linear rate, etc. These problems can significantly impact the flow behaviour in a micro-nozzle resulting in relatively poor performance compared to a traditional macro-scale nozzle. The objective of this research work is to design a flat micro convergent nozzle which will be capable of providing the required thrust ( <100 μN) with water vapour as a fluid through it. The extreme conditions of space and micro size of the nozzle make this research very interesting. 2D Numerical simulations were carried out on the micro-nozzle with the help of ANSYS Fluent to observe the state of fluid at all the region inside. Inlet conditions were chosen such that the desired thrust was achieved and single phase flow inside was ensured. For more realistic results, ambient conditions of space were also imposed at outlet like pressure <10 Pa and temperature around 4 K. At the end, the results were compared with inviscid isentropic flow.
Keywords: propulsion, nanosat, sonic flow, microfluidics, convergent nozzle, simulations