Rene Pecnik

Understanding the impact of compressibility effects on turbulent flows is crucial for a wide range of engineering applications, as they influence the performance, efficiency and reliability of aerospace vehicles, gas turbines, and heat exchangers. Turbulence in compressible flow involves two main mechanisms: heat transfer and intrinsic compressibility effects, also termed ‘true’ compressibility in turbulence. Heat transfer mainly causes mean variations in density and viscosity, and density fluctuations due to entropy changes. In contrast, intrinsic compressibility effects are associated with volume changes in response to pressure fluctuations.

In this talk, we will discuss how these mechanisms can be effectively characterized and modeled. The effects of heat transfer on the mean flow - captured by changes in friction velocity and viscous length scales - naturally lead to a semi-local scaling framework, whose origins trace back to the work of Morkovin (1962) and van Driest (1951). We present a generalized version of this framework, which enables the derivation of scaling laws and provides guidance for improving turbulence models. In contrast, intrinsic compressibility effects alter near-wall turbulence dynamics through dilatational motions that counteract the ejection and sweep events driven by mean streamwise vortices. These effects, too, can be incorporated into scaling laws and turbulence closures, allowing for models that are robust across a wide range of conditions - from low to high Mach numbers and from ideal to non-ideal fluids.

Biography

Rene Pecnik is Professor of Energy Technology at the Delft University of Technology in the Netherlands. He earned his PhD in Mechanical Engineering from Graz University of Technology, Austria, in 2007. His doctoral research specialized in the numerical modeling of aerodynamic flows in transonic gas turbines, focusing on unsteady effects and laminar-to-turbulent boundary layer transition. Following his PhD, he joined the Center for Turbulence Research at Stanford University as a postdoctoral fellow, where he worked on simulations of reacting turbulent flows in hypersonic propulsion systems. In 2010, he moved to the Netherlands to continue his academic career at TU Delft. Pecnik’s research bridges fundamental studies and applied developments. He aims to advance knowledge in fluid mechanics and turbulence while collaborating closely with industry on thermal energy conversion technologies. His areas of expertise include turbulent heat transfer, radiative transfer, turbulence modeling, supercritical fluids, unsteady turbomachinery flows, direct numerical simulations, and high-performance computing. He serves on several scientific committees and currently chairs the organizing/scientific committee for the European Symposium on Supercritical CO₂ Power Cycles.