# Direct numerical simulation of high-pressure mixing in turbulent jets

## TL;DR

This paper uses direct numerical simulations to compare high-pressure turbulent jet mixing at subcritical and supercritical conditions, revealing differences in flow dynamics and mixing behavior relevant to combustion applications.

## Contribution

It provides detailed DNS analysis of turbulent jet mixing at supercritical pressures, highlighting differences from subcritical conditions in flow statistics and mixing characteristics.

## Key findings

- Supercritical jets lack distinct liquid-gas phase separation.
- Flow dynamics differ significantly between subcritical and supercritical conditions.
- Mixing efficiency and jet development are altered at supercritical pressures.

## Abstract

Combustion in automotive and aerospace applications employing diesel, gas turbine and liquid rocket engines is preceded by injection and mixing of fuel and oxidizer at high pressures, often exceeding mixture critical values. Experimental observations indicate that the jets injected at supercritical pressures exhibit significantly different dynamics than the jets at subcritical conditions, owing to the lack of distinct liquid and gas phases in supercritical state. As a result, the averaged flow quantities such as the potential core length, jet spatial growth rate and velocity decay profiles differ in the two conditions, resulting in different mixed-fluid distributions. In this study, turbulent jet direct numerical simulations (DNS) are performed to examine the variations in statistics between injection of Nitrogen ($\mathrm{N_{2}}$) in Nitrogen ($\mathrm{N_{2}}$) at subcritical (perfect-gas) and supercritical conditions. Isothermal round jets at Reynolds number ($Re_{D}$), based on jet diameter ($D$) and jet orifice velocity ($U_{0}$), of $5000$ and Mach number of $0.6$ are considered. For mixing analyses, a passive scalar transported with the flow is examined.