Session: 13-02 Heat Transfer Testing & Instrumentation

Submission Number: 176959

A Dimensionless Design Framework and Mechanistic Study of a Perforated-Wall Transverse-Jet Mixer for Rapid Cooling of High-Temperature Gas Streams 

In current research and development on aeroengine combustors, the main combustor and the afterburner are often tested separately. As a result, the thermal energy of the main-combustor exhaust is wasted, while the afterburner requires an external supply of high-temperature air at its inlet, driving up testing costs. If the main-combustor exhaust could be repurposed to provide appropriate inlet conditions for the afterburner and both units were integrated on a single test platform for simultaneous operation, the overall cost would be markedly reduced. A key challenge, however, is that the main-combustor exhaust temperature is substantially higher than the required inlet temperature for the afterburner. In practical engines, this temperature reduction is achieved by the enthalpy drop across the turbine. Because installing a turbine on a test rig is costly and mechanically complex (due to the required shaft arrangement), a perforated-wall mixer was designed to achieve an equivalent temperature reduction via dilution and mixing. In this configuration, low-temperature air is injected through an annular array of small wall holes as transverse jets that mix with the hot mainstream to achieve rapid cooling. Although transverse-jet mixing has been extensively studied, the mutual interference among multiple jets under large temperature and mass-flow ratios has not been adequately addressed.

To develop a comprehensive understanding of how alternative geometries modulate inter-jet interference, and subsequently optimize the mixer to achieve efficient cooling over a short mixing distance, we employed both experimental and numerical approaches. The study consists of three parts. First, two dimensionless parameters were introduced to establish a design framework for the mixer, accounting for practical geometric constraints on hole number and diameter. Second, experiments were performed on three representative configurations, and radial temperature distributions at multiple downstream locations were measured with thermocouple rakes to validate the numerical methodology. Third, sixteen configurations with different hole diameters and numbers were initially evaluated using Reynolds-averaged Navier–Stokes (RANS) simulations to assess mixing efficiency, and three selected configurations were subsequently investigated with large-eddy simulation (LES) to clarify the underlying flow and thermal mechanisms. The numerical predictions reasonably reproduced the measured downstream temperature distributions. The RANS results indicated that, at fixed momentum ratio, mixing efficiency increased and then decreased with hole number, whereas at fixed hole number, it first increased and then rapidly decreased with increasing momentum ratio. The LES analyses further revealed that, for a constant momentum ratio, increasing hole number initially enhances mixing through vortex interaction but eventually reduces efficiency due to decreased jet spacing and intensified dissipation. Conversely, at fixed hole number, increasing jet momentum initially improves mixing through stronger penetration but ultimately weakens it by limiting lateral jet coverage. The proposed mixer design establishes clear correlations among geometric parameters, flow conditions, and mixing performance, providing a practical basis for integrated combustor–afterburner testing.

Presenting Author: Hongyu Ju School of Power and Energy, Northwestern Polytechnical University

Presenting Author Biography: A doctoral candidate who completed his undergraduate studies at Northwestern Polytechnical University, where he was recommended for admission to the master’s program without examination and subsequently continued his doctoral studies. His major is Power Engineering and Engineering Thermophysics, and his research focuses on combustion chambers of aero engines, including flow dynamics, combustion characteristics, ignition behavior, and efficient cooling and mixing processes.

Authors:

Hongyu Ju School of Power and Energy, Northwestern Polytechnical University
Jianqin Suo School of Power and Energy, Northwestern Polytechnical University
Hongxia Liang School of Power and Energy, Northwestern Polytechnical University
Yue Li School of Power and Energy, Northwestern Polytechnical University
Jingxu Lu School of Power and Energy, Northwestern Polytechnical University
Longxi Zheng School of Power and Energy, Northwestern Polytechnical University