Determining the Hydrogen Mass Fraction, Concentration Distributions and Related Flow Properties in a Subsonic Turbulent Mixing Region with a Multi-Species Co-Flow

Abstract

Distributions of the injectant mass fraction and concentration along and across the downstream mixing region of an injectant plume in a subsonic air flow are determined experimentally by using a standard traversing rig holding three probes for four simultaneous flow measurements. A standard pitot-static probe measures the stagnation and static pressures (P0, ps), a second probe measures the stagnation temperature (T0), and a third probe measures the static temperature (Ts). The flow velocity is not measured but can be predicted in this approach, so particle-imaging velocimetry is not required. The four measurements (P0, ps, T0, Ts) are combined with a special gas dynamics analysis to provide a method for determining downstream distributions of the mass fractions and concentration of the injectant, subsonic flow Mach number, flow velocity and the molecular weights and specific heat ratios of the mixture of injectant and air. The flow properties are determined uniquely at each local point in the flow by using a small set of simultaneous algebraic equations in the unknowns. For mixtures consisting of the injectant hydrogen in co-flowing subsonic air, the results of the present method are in good agreement with the test results obtained from a wind tunnel model of a turbulent mixing flow field computed with the NASA VULCAN computer code. The method presented in this paper, as well as earlier alternative methods developed by the authors, is based on well-established gas dynamic principles and equations. Some earlier work was developed specifically for supersonic flows (AIAA papers 2006–3359 and 2008–2656) and other work for subsonic flows with different values of the specific heat ratio (AIAA paper 2009–4048), while the current method applies to subsonic flows with mixtures of H2/air and H2/N2/O2 for which the specific heat ratios of the injectant and co-flowing gas are very similar. The method presented is also generalized for mixtures of multicomponent co-flows using the approach described in the AIAA paper 2009–4048. The application of this method to determine the mass fractions of all components in turbulent mixing regions of multi-component mixtures in different cross sections of the combustion chamber of turbojet, turbofan and ramjet engines will allow estimations of the concentrations of species such as CO and NOx in different mixtures and should help design engines to reduce harmful emissions from such oxides.