In this talk, I will present some of the research conducted in my group at NTNU over the last few years. First, I will present our most recent work on the effect of increasing levels of hydrogen enrichment on the nonlinear response (saturation) of forced premixed flames and discuss why increasing hydrogen leads to a flame response that remains approximately linear at increasingly high forcing amplitudes.
In the second part, I will present some of our work on entrainment across the turbulent, non-turbulent interface (TNTI) in turbulent jets where we used time-resolved OH-PLIF and PIV to simulataneously track the evolution of the jet boundary and evaluate the balance between the local entrainment velocity and surface area using a multi-scale fractal approach. This work showed that the mean entrainment velocity scales at a rate that balances the scaling of the surface area of the TNTI. The use of spatial filtering shows that at the smallest scales, the entrainment velocity is small but is balanced a very large surface area, whilst at the largest scales the entrainment velocity is large but is balanced by a smaller (smoother) surface area.
In the final part of the talk, I will present the response of an axisymmetric jet placed at various positions in a standing wave oriented normally to the jet. At the velocity and pressure nodes the axisymmetric (m=0) and first azimuthal (m=±1) modes are excited through manipulation of the jet exit boundary conditions. At positions between the nodes, both the m=0 and m=±1 modes are simultaneously excited resulting in asymmetric forcing caused by a phase difference between the transverse and longitudinal acoustic fluctuations leading to the asymmetric formation of vortices in the near field and bifurcating the jet into two or more momentum streams downstream.