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The present work builds upon the diagnostic plot for the streamwise turbulence intensity [Alfredsson & Örlü, 2010] and generalises it for higher-order (even and odd) moments providing a general description of the probability density distribution of streamwise velocity fluctuations. Turbulent boundary layers (up to a friction Reynolds number of...
conference paper 2015
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One-dimensional turbulence (ODT) is a stochastic simulation in which 3D turbulence effects are captured on a notional 1D line of sight by introducing instantaneous spatial re-arrangements (maps) that represent advection by notional turbulent eddies. These eddy events incorporate the possibility of kinetic-energy changes that are equal and...
conference paper 2015
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Convection in an inclined layer generates various types of spatio-temporal patterns due to interaction of buoyancy and shear. At small angles of incline, the secondary instability of the uniform base state occurs in the form of buoyancy dominated longitudinal rolls. Above a critical angle of incline marking a co-dimension 2 point, shear driven...
conference paper 2015
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Measurements of turbulent flow in a horizontal pipe subjected to wall transpiration are presented. Results include data on global flow rates and pressure drop, and local mean and fluctuating velocity profiles. Two distinct flow transpiration rates are studied, $v_w^{++}$ = $v_w$/$U_m$ = 0.0005 and 0.001. The effects of flow transpiration on the...
conference paper 2015
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The natural turbulent convection of liquid sodium in a cell with end heat exchangers providing a fixed temperature drop is investigated experimentally. The cell is a straight thermally isolated tube with inner diameter D = 96 mm and length L ≈ 20D. Experiments are carried out for a fixed Rayleigh number Ra = 2.4 • 10^6 and for different tube...
conference paper 2015
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Oscillating pipe flows, with zero mean velocity, are common in engineering systems and particularly in Stirling-based engines and heat pumps, e.g. pulse-tube cryogenic coolers. These flows are particularly challenging to model because their flow state depends on both the Reynolds number and the dimensionless frequency or Womerlsey number. A...
conference paper 2015
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We have developed a new spectral method to simulate flows with very fine boundary layers present. We apply it to calculate the evolution of freely decaying MHD turbulence between isolating walls. By comparison them with results obtained in fully periodic domain we quantify the influence of the channel walls on the character of freely decaying...
conference paper 2015
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Statistical properties of turbulent Rayleigh-Bénard convection (RBC) are investigated experimentally in a cylindrical cell of aspect ratio one. We specifically analyze the large scale circulation of RBC based on measurements of temperature fluctuations by small Ge sensors placed inside the cell. The resulting dependencies of Reynolds numbers on...
conference paper 2015
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The dynamics of turbulent flow at finite magnetic Reynolds numbers can be very complex due to the coupled nature of the evolution equations for the flow and magnetic fields. In this regime, the Hartmann flow in a straight rectangular duct with streamwise periodicity is studied with the help of direct numerical simulations (DNS) and the effect of...
conference paper 2015
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An explicit algebraic and differential Reynolds stress models (EARSM and DRSM) are used to investigate the influence of homogeneous shear and compression on the behaviour of turbulence in the limit of rapid distortion theory (RDT). EARSM is shown to give realizable results and to preserve RDT regime, unlike the eddy-viscosity model (EVM). The...
conference paper 2015
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A wide body of research exists which explores the effects of surface roughness or patterned wall shapes on instability growth and transition. Building on those works as well as recent experiments demonstrating passive laminar flow control using arrays of discrete roughness [3, 8], a set of spanwise-wavy walls is designed with the goal of...
conference paper 2015
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This work is concerned with the numerical investigation of the linear stability properties of the viscous, incompressible flow inside a toroidal pipe. A Hopf bifurcation is found and tracked in phase space, showing that the flow is modally unstable even at extremely low curvatures. The bifurcation and the eigenfunctions associated with it are...
conference paper 2015
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We conduct computations of rotating Rayleigh-Bénard convection in the so-called geostrophic regime, characterized by strong thermal forcing (high Rayleigh numbers) and strong rotation (small Ekman numbers). We employ the full Navier-Stokes equations in our computations and compare no-slip and stress-free boundaries for the plates. The Ekman...
conference paper 2015
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Stratified shear flows are ubiquitous in geophysical systems such as oceanic overflows, wind-driven thermoclines, and atmo- spheric inversion layers. The stability of such flows is governed by the Richardson Number Ri which represents a balance between the stabilizing influence of stratification and the destabilizing influence of shear. For a...
conference paper 2015
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In hydraulic turbines, the tip-leakage vortex is responsible for flow instabilities and for promoting erosion due to cavitation. To better understand the flow in the tip region, LES computations are carried out to compute the flow around a NACA0009 blade including the gap between the tip and the wall. The influence of the gap size is...
conference paper 2015
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Particle impaction on a cylinder in a cross flow is investigated with the use of Direct Numerical Simulations (DNS), with a focus on the effect of turbulence on the impaction efficiency. It is found that for particles with Stokes numbers in the boundary stopping mode there is up to ten times more front side impaction for turbulence with a large...
conference paper 2015
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The Coupled Wake Boundary Layer (CWBL) model combines a classical wake model with a ``top-down'' boundary layer model through two-way coupling to combine the strengths of these two analytical modeling approaches. The wake model part of the CWBL model captures the effects of the relative turbine positioning and the growth of wakes due to...
conference paper 2015
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We consider the spatio-temporal aspects of the transition to turbulence in a boundary layer above a flat plate exposed to free-stream turbulence. Combining results from the receptivity to free-stream turbulence with the observation of a double threshold from transition studies in e.g. pipe flow we arrive at a physically motivated prediction for...
conference paper 2015
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Bos, W. (author), Kadoch, B. (author), Schneider, K. (author)
The angle between subsequent particle displacement increments is evaluated as a function of the timelag in isotropic turbulence. It is shown that the evolution of the average of this angle contains two well-defined power-laws, reflecting the multi-scale dynamics of high-Reynolds number turbulence.
conference paper 2015
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The decay of compressible homogeneous isotropic turbulence for dense gases is studied by means of Direct Numerical Simulations and Implicit Large Eddy Simulations. A family of heavy fluorocarbons, which exhibit non-classical phenomena, is considered. The thermodynamic behavior of the fluids is modeled by the politropic Van der Waals or the five...
conference paper 2015
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