Experimental study of oscillating-grid turbulence interacting with a solid boundary

The interaction between oscillating-grid turbulence and a solid, impermeable boundary (positioned below, and aligned parallel to, the grid) is studied experimentally. Instantaneous velocity measurements, obtained using two-dimensional particle imaging velocimetry in the vertical plane through the centre of the (horizontal) grid, are used to study the effect of the boundary on the root-mean-square velocity components, the vertical flux of turbulent kinetic energy (TKE) and the terms in the Reynolds stress transport equation. Identified as a critical aspect of the interaction is the blocking of a vertical flux of TKE across the boundary-affected region. Terms of the Reynolds stress transport equations show that the blocking of this energy flux acts to increase the boundary-tangential turbulent velocity component, relative to the far-field trend, but not the boundary-normal velocity component. The results are compared with previous studies of the interaction between zero-mean-shear turbulence and a solid boundary. In particular, the data reported here are in support of viscous and ‘return-to-isotropy’ mechanisms governing the intercomponent energy transfer previously proposed, respectively, by Perot & Moin (J. Fluid Mech., vol. 295, 1995, pp. 199–227) and Walkeret al.(J. Fluid Mech., vol. 320, 1996, pp. 19–51), although we note that these mechanisms are not independent of the blocking of energy flux and draw parallels to the related model proposed by Magnaudet (J. Fluid Mech., vol. 484, 2003, pp. 167–196).

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Shear-free turbulence near a wall

Journal of Fluid Mechanics ◽

10.1017/s0022112097005065 ◽

1997 ◽

Vol 338 ◽

pp. 363-385 ◽

Cited By ~ 23

Author(s):

DAG ARONSON ◽

ARNE V. JOHANSSON ◽

LENNART LÖFDAHL

Keyword(s):

Reynolds Stress ◽

Initial Response ◽

Wall Turbulence ◽

Major Influence ◽

Grid Turbulence ◽

Normal Velocity ◽

Reynolds Stresses ◽

Mean Velocity ◽

Wall Interaction ◽

Near Wall

The mean shear has a major influence on near-wall turbulence but there are also other important physical processes at work in the turbulence/wall interaction. In order to isolate these, a shear-free boundary layer was studied experimentally. The desired flow conditions were realized by generating decaying grid turbulence with a uniform mean velocity and passing it over a wall moving with the stream speed. It is shown that the initial response of the turbulence field can be well described by the theory of Hunt & Graham (1978). Later, where this theory ceases to give an accurate description, terms of the Reynolds stress transport (RST) equations were measured or estimated by balancing the equations. An important finding is that two different length scales are associated with the near-wall damping of the Reynolds stresses. The wall-normal velocity component is damped over a region extending roughly one macroscale out from the wall. The pressure–strain redistribution that normally would result from the Reynolds stress anisotropy in this region was found to be completely inhibited by the near-wall influence. In a thin region close to the wall the pressure–reflection effects were found to give a pressure–strain that has an effect opposite to the normally expected isotropization. This behaviour is not captured by current models.

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Analysis of Interaction between Turbulence generated by Settling Particles and Oscillating Grid Turbulence

PROCEEDINGS OF HYDRAULIC ENGINEERING ◽

10.2208/prohe.38.571 ◽

1994 ◽

Vol 38 ◽

pp. 571-576

Author(s):

Masahiro TAMAI ◽

Kohji MURAOKA

Keyword(s):

Grid Turbulence ◽

Settling Particles ◽

Oscillating Grid

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Design Method for Subsonic and Transonic Cascade With Prescribed Mach Number Distribution

Journal of Turbomachinery ◽

10.1115/1.2929179 ◽

1992 ◽

Vol 114 (3) ◽

pp. 553-560 ◽

Cited By ~ 35

Author(s):

O. Le´onard ◽

R. A. Van den Braembussche

Keyword(s):

Mach Number ◽

Flow Field ◽

Pressure Distribution ◽

Velocity Component ◽

Design Method ◽

Normal Velocity ◽

Flow Solver ◽

Number Distribution ◽

Mach Number Distribution ◽

Transonic Cascade

A iterative procedure for blade design, using a time marching procedure to solve the unsteady Euler equations in the blade-to-blade plane, is presented. A flow solver, which performs the analysis of the flow field for a given geometry, is transformed into a design method. This is done by replacing the classical slip condition (no normal velocity component) by other boundary conditions, in such a way that the required pressure or Mach number distribution may be imposed directly on the blade. The unknowns are calculated on the blade wall using the so-called compatibility relations. Since the blade shape is not compatible with the required pressure distribution, a nonzero velocity component normal to the blade wall evolves from the new flow calculation. The blade geometry is then modified by resetting the wall parallel to the new flow field, using a transpiration technique, and the procedure is repeated until the calculated pressure distribution has converged to the required one. Examples for both subsonic and transonic flows are presented and show a rapid convergence to the geometry required for the desired Mach number distribution. An important advantage of the present method is the possibility to use the same code for the design and the analysis of a blade.

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Full-bore crank-angle resolved imaging of combustion in a four-stroke gasoline direct injection engine

Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering ◽

10.1243/09544070jauto542 ◽

2007 ◽

Vol 221 (10) ◽

pp. 1305-1320 ◽

Cited By ~ 4

Author(s):

H Ma ◽

S Marshall ◽

R Stevens ◽

R Stone

Keyword(s):

Direct Injection ◽

Vertical Plane ◽

Cylinder Liner ◽

Light Sheet ◽

Diagnostic Techniques ◽

Gasoline Direct Injection ◽

Radius Of Curvature ◽

Piston Crown ◽

Soot Loading ◽

Particle Imaging

The conventional Bowditch piston arrangement in an optical access engine limits the field of view to about half the bore area. By using a transparent crown (with a flat top) and incorporating a concave surface into the underside of the piston, then the piston crown acts as a diverging lens. Appropriate choice of the radius of curvature and the piston crown thickness provides an image of the full bore. There is of course optical distortion in the image but, since the piston position is known for each image, then it is comparatively simple to reconstruct undistorted images and videos. As an illustration of the technique, results are presented here for flame front tracking, and estimates of the combustion temperature and soot loading by a colour ratio pyrometry technique. This full-bore imaging technique is also applicable to many other optical diagnostic techniques. For a motored engine with particle imaging velocimetry and an optical cylinder liner, then the light sheet could enter either through the piston to illuminate a vertical plane or through the cylinder liner and be imaged through the piston. The choice of laser-based combustion diagnostic techniques would be limited by the transmission range of the piston window.

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Study on interaction between turbulence generated by uniformly fallng particles and oscillating grid turbulence.

Doboku Gakkai Ronbunshu ◽

10.2208/jscej.1995.521_49 ◽

1995 ◽

pp. 49-58

Author(s):

Masahiro Tamai ◽

Kohji Muraoka ◽

Kazuhiro Shimizu

Keyword(s):

Grid Turbulence ◽

Oscillating Grid

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Drag reduction and turbulent structure in two-dimensional channel flows

Philosophical Transactions of the Royal Society of London Series A Physical and Engineering Sciences ◽

10.1098/rsta.1991.0064 ◽

1991 ◽

Vol 336 (1640) ◽

pp. 19-34 ◽

Cited By ~ 43

Keyword(s):

Shear Stress ◽

Drag Reduction ◽

Strain Rate ◽

Reynolds Stress ◽

Polymer Concentration ◽

Turbulent Structure ◽

Channel Flows ◽

Channel Height ◽

Normal Velocity ◽

Two Dimensional

A two-component laser velocimeter has been used to determine the effect of wall strain rate, polymer concentration and channel height upon the drag reduction and turbulent structure in fully developed, low concentration, two-dimensional channel flows. Water flows at equal wall shear stress and with Reynolds numbers from 14430 to 34640 were measured for comparison. Drag reduction levels clearly depended upon wall strain rate, polymer concentration and channel height independently.However, most of the turbulent structure depended only upon the level of drag reduction. The slope of the logarithmic law of the wall increased as drag reduction increased. Similarly, the root-mean-square of the fluctuations in the streamwise velocity increased while the r.m.s. of the fluctuations in the wall-normal velocity decreased with drag reduction. The production of the streamwise normal Reynolds stress and the Reynolds shear stress decreased in the drag-reduced flows. Therefore it appears that the polymer solutions inhibit the transfer of energy from the streamwise to the wall-normal velocity fluctuations. This could occur through inhibiting the newtonian transfer mechanism provided by the pressure-strain correlation. In six drag-reducing flows, the sum of the Reynolds stress and the mean viscous stress was equal to the total shear stress. However, for the combination of highest concentration (5 p.p.m.), smallest channel height (25 mm) and highest wall strain rate (4000 s - 1 ), the sum of the Reynolds and viscous stresses was substantially lower than the total stress indicating the presence of a strong non-newtonian effect. In all drag-reducing flows the correlation coefficient for uv decreased as the axes of principal stress for the Reynolds stress rotated toward the streamwise and wall-normal directions.

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Routes to Dissipation under Different Dynamical Conditions

Journal of Physical Oceanography ◽

10.1175/jpo-d-14-0205.1 ◽

2015 ◽

Vol 45 (8) ◽

pp. 2149-2168 ◽

Cited By ~ 18

Author(s):

Nils Brüggemann ◽

Carsten Eden

Keyword(s):

Energy Flux ◽

Velocity Component ◽

Functional Relationship ◽

Baroclinic Instability ◽

Viscous Friction ◽

Ocean Model ◽

Global Ocean ◽

Small Scale ◽

Ocean Energy ◽

Global Estimate

AbstractIn this study, it is investigated how ageostrophic dynamics generate an energy flux toward smaller scales. Numerical simulations of baroclinic instability are used with varying dynamical conditions ranging from quasigeostrophic balance to ageostrophic flows. It turns out that dissipation at smaller scales by viscous friction is much more efficient if the flow is dominated by ageostrophic dynamics than in quasigeostrophic conditions. In the presence of ageostrophic dynamics, an energy flux toward smaller scales is observed while energy is transferred toward larger scales for quasigeostrophic dynamics. Decomposing the velocity field into its rotational and divergent components shows that only the divergent velocity component, which becomes stronger for ageostrophic flows, features a downscale flux. Variation of the dynamical conditions from ageostrophic dynamics to quasigeostrophic balanced flows shows that the forward energy flux and therefore the small-scale dissipation decreases as soon as the horizontal divergent velocity component decreases. A functional relationship between the small-scale dissipation and the local Richardson number is estimated. This functional relationship is used to obtain a global estimate of the small-scale dissipation of 0.31 ± 0.23 TW from a high-resolution realistic global ocean model. This emphasizes that an ageostrophic direct route to dissipation might be of importance in the ocean energy cycle.

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On the Use of Direct and Inverse Numerical Flow Calculations for Supersonic Turbine Design

Volume 1: Turbomachinery ◽

10.1115/94-gt-320 ◽

1994 ◽

Author(s):

F. Pommel

Keyword(s):

Flow Field ◽

Euler Equations ◽

Velocity Component ◽

Normal Velocity ◽

Blade Design ◽

Blade Profile ◽

Flow Solver ◽

Time Marching ◽

Turbine Design ◽

Marching Method

A procedure for blade design, using a time marching method to solve the Euler equations in the blade-to-blade plane is presented. This procedure uses an Office Nationale d’Etude et de Recherches Aeronautique flow solver. The classical slip conditions (no normal velocity component along the blade profile) has been replaced by another boundary conditions in such a way that the required pressure may be imposed directly. The orignal direct code was therefore transformed into an inverse solver. The unknows are calculated on the blade wall using the so-called compatibility relations. The blade geometry is then modified by resetting the wall parallel to the new flow field. The results obtained with this design process for a supersonic turbine blade of a space turbopump is presented.

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