Abs t r ac t . Recent developments concerning the connection between notions of hydrodynamic stability usually associated with stationary laminar flows-and dynamics, most notably turbulent fluid flows, are reviewed. Based on a technical device originally introduced by Hopf in 1941, a rigorous mathematical relationship between criteria for nonlinear energy stability and bounds on global t ranspo...

Laminar and turbulent natural convection inside concentric spherical shells with isothermal cold and hot boundaries is numerically investigated up to Rayleigh number values Ra 6 10 and Pr = 0.71. The study utilizes direct numerical simulation (DNS), large eddy simulation (LES) and Reynolds averaged Navier– Stokes (RANS) approaches for investigation of the laminar, transitional and fully develop...

Direct numerical simulation was used to study laminar and turbulent flows in circular pipes with smoothly corrugated walls. The corrugation wavelength was kept constant at 0.419D, where D is the mean diameter of the wavy-wall pipe and the corrugation height was varied from zero to 0.08D. Flow rates were varied in steps between low values that generate laminar flow and higher values where the fl...

The high cost of wind tunnel testing and the ongoing reduction in national wind tunnel facilities are forcing the aerospace engineering community to increasingly rely on computational fluid dynamics (CFD) to predict the performance of new aircraft designs. However, most aerospace applications are characterized by flows that exhibit large-scale unsteady turbulence and the accurate prediction of ...

Turbulent flows near walls have been the focus of intense study since their first description by Ludwig Prandtl over 100 years ago. They are critical in determining the drag and lift of an aircraft wing for example. Key challenges are to understand the physical mechanisms causing the transition from smooth, laminar flow to turbulent flow and how the turbulence is then maintained. Recent direct ...

The article presents the analysis of the processes occurring together with the turbulent transfer of impulse in mixture of hydrocarbon fluid and polymer solutions (antiturbulent additives). The study evaluates complex shear flows by popular theoretical and practical methods. Understanding of hydrodynamic and dissipative effects of laminar-turbulent transition tightening and turbulence suppressi...

Direct numerical simulation (DNS) is applied to investigate properties of katabatic and anabatic flows along thermally perturbed (in terms of surface buoyancy flux) sloping surfaces in the absence of rotation. Numerical experiments are conducted for homogeneous surface forcings over infinite planar slopes. The simulated flows are the turbulent analogs of the Prandtl (1942) one-dimensional lamin...

The transition to turbulence in pipe flow does not follow the scenario familiar from RayleighBenard or Taylor-Couette flow since the laminar profile is stable against infinitesimal perturbations for all Reynolds numbers. Moreover, even when the flow speed is high enough and the perturbation sufficiently strong such that turbulent flow is established, it can return to the laminar state without a...

Roughness elements in high speed flows can cause laminar-turbulent transition leading to higher heating rates and drag. Transition of flow past a hemispherical bump placed on a flat plate is explored in this paper for three Mach numbers [3.37, 5.26, 8.23] using direct numerical simulation on unstructured grids. The simulation parameters are chosen to match the experiments carried out by Danehy ...

We consider the evolution of arbitrarily large perturbations a prescribed pure hydrodynamical flow an electrically conducting fluid. study whether as well generated magnetic fields decay or grow with time and constitute dynamo process. For that purpose we derive generalized Reynolds-Orr equation for sum kinetic energy hydrodynamic perturbation energy. The is confined in finite volume so normal ...