Electromagnetic effects in cylindrical pipe flow

Mechanical Maritime and Materials Engineerin

Direct numerical simulation of turbulent pipe at high Reynolds numbers, velocity statistics and large scale motions

In recent years there has been a considerable research effort dedicated to turbulent pipe flow. Topics of interest are, amongst others, the scaling of near wall turbulent statistics and the existence of very large scale turbulent structures at higher Reynolds numbers. These structures have been observed experimentally in boundary layers, Hutchins & Marusic (2007) and pipes, Monty et al. (2007). Recently these structures have also been observed in moderate Reynolds number direct numerical simulations of channel and boundary layer flows. In this paper we will report on the simulation of turbulent pipe flow at bulk Reynolds numbers of 24600, 37500, and 75,000. The numerical grid (up to 7.6e9 grid nodes) is comparable to the grid used by Jimenez & Hoyas (2008) and should be sufficiently fine to resolve all scales. At high Reynolds numbers we observe some evidence of the aforementioned long scale structures.Energy Technolog

Direct numerical simulation of turbulent pipe flow at high Reynolds numbers: Extended abstract

With todays supercomputers we are able to simulate flows with moderate to high Reynolds numbers. These flows show features that are not present in simulations with lower Reynolds numbers. Recently we have finished a fully resolved direct numerical simulation of a turbulent pipe flow with a bulk Reynolds number of 76,000 on a computational domain which is 18 pipe diameters long. During the conference we will present results from this simulation, such as velocity statistics, pre-multiplied energy spectra and auto correlations.Process and EnergyEnergy Technolog

The use of immersed boundary methods for the calculation of flow around objects

This article discusses the use of immersed boundary methods for the flow around objects. Treated are the reasons for their use, their benefits compared to other methods, their importance, and possible further developments.Mechanical, Maritime and Materials Engineerin

An experimental study on friction reducing polymers in turbulent pipe flow

An experimental study was conducted to search the reduction of friction in fully developed turbulent pipe flow using different types of polyacrylamides as friction reducing polymers. Pressure drop measurements determined the friction reduction. Three different polymer types Superfloc A110, Superfloc A130 and Superfloc A150 were used to examine the effect of polymer concentration, Reynolds number and polymer type on friction reduction. The Darcy friction factor was obtained for each polymer type at the polymer concentration ranging from 0 to 500 wppm and a Reynolds number range of 10000-80000. It was observed that friction factor decreased with increment in polymer concentration and Reynolds number for each polymer. Higher molecular weight polymers are more effective at reducing friction. With increasing concentration of polymer, the measured data approaches the Virk asymptote, which represents the maximum friction reduction limit by the polymers. The percentage of friction reduction increased with increasing concentration of polymer up to 100 wppm for each polymer type and then began to decrease for polymer concentrations higher than 100 wppm. An empirical formula was obtained to calculate the Darcy friction factor as a function of Reynolds number and polymer concentration for Superfloc A110.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Marine and Transport Technolog

Direct numerical simulation of homogeneous turbulence in combination with premixed combustion at low Mach number modelled by the G-equation

Mechanical, Maritime and Materials Engineerin

An Immersed Boundary Method for Complex Flow and Heat Transfer

The need to predict flow and heat transfer problems requires a flexible and fast tool able to simulate complex geometries without increasing the complexity of the flow solver architecture. Here we use a finite volume code that uses a direct solver with pressure correction. A new immersed boundary method (IBM) is used for a geometry consisting of a square body in a flow. The method is applied to flow cases with and without heat transfer. The obstacle simulated in the domain is implemented by local forcing of the flow with a procedure that adjusts locally the shear stress at the position of the object in conjunction with a non-penetration condition on the body walls. This approach has already been successfully applied by Breugem and Boersma (Phys. Fluids 17:15, 2005). We extend it for the case of heat transfer between body and flow. Comparison with other methods has been carried out as well. However, the proposed method can not be simply extended to immersed boundaries not aligned with the grid.Process and EnergyMechanical, Maritime and Materials Engineerin

Detection of turbulent/non-turbulent interface for an axisymmetric turbulent jet: Evaluation of known criteria and proposal of a new criterion

In this paper, we evaluate several criteria for the detection of turbulent/non-turbulent interface using direct numerical simulation and particle image velocimetry data of an axisymmetric turbulent jet. The possibility of identifying the interface from information available in wholefield velocity data alone is also explored. The present results using a Concentration thresholding technique compare well against available results obtained using a similar detection criterion. It is noted that Concentration and Vorticity criteria are difficult to apply with standard PIV data and therefore a new criterion based on azimuthal vorticity and streamwise velocity—quantities available from such data, is proposed. The proposed criterion scores over previously employed criteria in terms of its simplicity of evaluation, and can possibly be applied to other flows not tested here. The instantaneous location of the interface as detected from the different criteria differs substantially. However, the conditionally averaged streamwise velocity, azimuthal vorticity, and Reynolds shear stress across the interface obtained from the new criterion, as well as from the previous criteria, agree reasonably well against available results. The present work further suggests that different criteria, even with slightly sub-optimal threshold value, can provide quantitatively similar ensemble-averaged results.Process and EnergyMechanical, Maritime and Materials Engineerin

Transient energy growth modulation by temperature dependent transport properties in a stratified plane Poiseuille flow

We investigate the effect of temperature dependent thermal conductivity ? and isobaric specific heat c_P on the transient amplification of perturbations in a thermally stratified laminar plane Poiseuille flow. It is shown that for decreasing thermal conductivity the maximum transient energy growth is amplified with respect to the ?=1 case, while the opposite occurs for increasing ?. A reversed mechanism is induced by a variable c_p. Substantial maximum growth enhancement/suppression is found in the range of Prandtl numbers Pr which encompasses most fluids of practical interest. The relative growth modulation shows an optimum Pr under spanwise perturbations. For energy amplifying property distributions a speed-up of the transient to reach the maximum energy growth is observed at low Pr, while a slow-down is found at large Pr. The opposite is true when the property variations suppress the growth of perturbations.Process and EnergyMechanical, Maritime and Materials Engineerin

A study on the application of two different acoustic analogies to experimental PIV data

The aim of the present study is to compare two different acoustic analogies applied to time-resolved particle image velocimetry (PIV) data for the prediction of the acoustic far-field generated by the flow over a rectangular cavity. We consider the model problem of sound radiating from an open, two-dimensional, shallow cavity with an aspect ratio of 2 at a Reynolds number of 3.0?×?104 (based on the cavity length). The study is carried out by simultaneous high-speed two-dimensional PIV and sound measurements. The instantaneous flow field is obtained from the PIV measurements. The emitted sound is then calculated using Curle’s analogy and Vortex Sound Theory. To our knowledge, Vortex Sound Theory is used here for the first time in combination with time-resolved PIV data. The acoustic analogies are derived through rather different pathways, and the mathematical schemes used to solve the equations are sensitive in a different way to factors such as data resolution, noise level, and complexity of the geometry. Both methods indicate that the trailing edge of the cavity is the main sound source. The predictions of the acoustic field obtained by applying the two methods are analyzed and compared with the measured sound. For the presented case, the results show that both analogies estimate the overall sound pressure level quite well and that they give very similar results, both in total intensity and in the spectral distribution of the emitted sound.Process and EnergyMechanical, Maritime and Materials Engineerin