Comparative Analysis of Schemes to Form a Hydrogen-Air Mixture in the Radial Pylons Channel

Abstract

The study of the processes occurring in the scramjet is an important task. These processes include formation of a hydrogen-air mixture to the combustion chamber scramjet. The experimental study of such processes involves various difficulties. Therefore the use of mathematical models and numerical modeling to analyze such problems is of importance.In this paper we consider the formation of hydrogen-air mixture by injecting hydrogen into concurrent supersonic airflow by the radial pylons arranged in the three-dimensional channel with a central coaxial cylinder. As a basis of the geometric model, a channel of circular cross section is taken, which is a sector in axisymmetric formulation. In the channel pylons are set. The paper considers pylons of two different shapes, as well as two versions of their location in the channel. Pylons are different in height, fastening method, and different flow vortex generators (turbulator), designed to improve the mixing efficiency. The pylon №1 is attached to the channel wall and occupies no more than 1/3 of the channel radius in radial direction. The pylon №2 is located along the entire channel radius and fastened with its one side to the wall of the channel and with another one to the coaxial cylinder extending along the axis of symmetry. Pylons are distinguished by different flow turbulators designed to improve the mixing efficiency. Hydrogen injection is carried out from the pylon surface before a turbulator. Hydrogen injection angle relative to the axis of the channel in the case of the first turbulator arises from its geometry to be 12º, in the case of the second turbulator it is 0º (to reduce losses of the total flow pressure). We study the influence of the geometric shape of the pylons on characteristics of emerging hydrogen-air mixture flow.Research is conducted numerically on the basis of Reynolds equations for a turbulent motion of viscous multicomponent gas with k  turbulence model. The problem is solved on a computational grid of 300 thousand cells with the number of Courant CFL = 1. The equations are discretized by the method of control volume using the schemes of the second order of accuracy.It was shown that changing the geometry of the vortex generator can increase the intensity of mixing, but this decreases the penetration ability of hydrogen because of decreasing injection angle. At the same time, changing the turbulator shape causes deteriorating carburetion. A reduced efficiency of mixing in some areas reaches 37%. An additional turbulator available in the vicinity of the coaxial cylinder does not compensate for the loss of carburetion quality. The total pressure loss decreases when the hydrogen injection occurs at a zero angle to the channel axis.

Keywords

• hydrogen-air mixture
• total pressure loss
• pylons
• injection of hydrogen
• viscosity
• computational fluid dynamics