Numerical investigation of a three-port transfer matrix of a dual-swirler burner

The acoustic properties of a dual-swirl humid combustor are investigated numerically by determining its burner transfer matrix (BTM). The three-port BTM is computed using a combination of finite-element and finite-volume methods. Complex-valued matrix elements are obtained, where the imaginary part represents acoustic reactance and the real part acoustic resistance. Reactance is evaluated by solving the pressure wave equation in the frequency domain, whereas resistive effects are captured by solving the incompressible Navier–Stokes equations for a multi-component gas. Acoustic forcing is applied separately at each port using harmonic or broadband signals in the range 50–650 Hz. The resulting pressure and velocity responses at both inlets and the outlet are used to assemble the 3×3 BTM. The numerical BTM is compared with predictions from an extended l-ζ model. The effective length and pressure loss coefficient are identified by fitting the simulated matrix components to the model. However, extending the classical two-port l-ζ formulation to the present three-port configuration is found to be invalid, as indicated by non-zero coupling terms between the inlets and unrealistically large fitted parameters. Variations in operating conditions, including speed of sound and inlet momentum ratio, show only minor influence on the BTM.