Reactions Mechanisms Reduction While Modelling The High-Temperature Flows in Nozzles

Аuthors

Krioukov V. G.^*, Abdullin A. L.^**, Nikandrova M. N.^***, Iskhakova R. L.^****

Kazan National Research Technical University named after A.N. Tupolev, 10, Karl Marks str., Kazan, 420111, Russia

*e-mail: vkrioukov@mail.ru
**e-mail: ala2000@mail.ru
***e-mail: manivik@gmail.com
****e-mail: vkrujkov@kai.ru

Abstract

Modern models for high-temperature chemically non-equilibrium flows calculating in nozzles are based on the detailed chemical kinetics. For this purpose, a certain reaction mechanism is built into the model. An expert approach is usually used to substantiate (reduction) this mechanism. However, it requires significant time consumption, and is performed only by the experienced specialists.

However, a number of automated reduction methods (an automated approach) are already developed thus far, and widely used. The article proposes a procedure for reducing the reaction mechanisms for chemically non-equilibrium flows in aircraft engines nozzles. This procedure consists of two methods: DRGEP (Directed Relation Graph Error Propagation) method and method of engagement with an adaptive threshold. The DRGEP method is focused on selection of only unimportant species and removal them from reaction mechanism along with reaction triggering them. If insignificant reactions still remain in the mechanism, they are removed by the method of engagement.

This procedure is included in the program for calculating chemically non-equilibrium flows in a nozzle. It generates a reduced local mechanism (L-mechanism) from the initial (redundant) set of reactions for the given values of the parameters α_ok, P_ос , r_m. Joining the L-mechnisms, obtained with the other values of these parameters it is possible to form a global mechanism (G-mechanism) for the specified area of their variation.

The cre ate d procedure validation was performed for the combustion products flow in the profiled nozzles for the LRE engine fuel (“О₂ + kerosene” and “N₂O₄ + C₂H₈N₂”) for a wide range of variation: oxidant excess ratio ( α_ok = 0.7…1.2); pressure (P_ос = 20…100 atm.); minimum radius (r_m = 0.006….0.06 m) with a geometric degree of expansion f_a = 50.

With an acceptable error in the flow characteristics prediction:

a) G -mechanism recombination of the working medium “О₂ + kerosene” was reduced from 47 reactions and 16 substances to 15 reactions and 9 substances (H , H₂ , O , O₂ , CO₂ , H₂O , CO , OH , HCO);

b) G -mechanism recombination of the working medium “N₂O₄ + C₂H₈N₂” was reduced from 82 reactions and 26 substances to 27 reactions and 15 substances (H, H₂, O, O₂, CO₂, H₂O, CO, OH, N, N₂, NO, NH, HCO, HNO, N₂O).

Keywords:

nozzle, chemical non-equilibrium flows, reaction mechanism, reduction

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