| 1. |
- Löfdahl, Lennart, 1948, et al.
(författare)
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Determination of Derivative Moments using Two Slanted Hot-Wires and a Spectral method
- 1993
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Ingår i: Experiments in Fluids. ; 15, s. 393-400
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Tidskriftsartikel (refereegranskat)abstract
- A method to determine derivative moments using slanted hot-wires and a spectral method has been developed. The general idea is to minimize measuring volume by using only two hot-wires, and a post-processing of the measurement data. It is shown that the spectral method is equivalent to conventional determinations of correlations. The method developed has been tested in the self-preserving region of a plane wake by computing profiles of the Reynolds stresses as well as the derivative moments in the expression for the total energy dissipation. One term in this expression, which with conventional methods requires two triple-wires or four cross-wires, has been determined using the spectral method.
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| 2. |
- Löfdahl, Lennart, 1948, et al.
(författare)
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Influence of Different Sensor Configurations on the Turbulent Quantities in a Complex Three-Dimensional Flow Field
- 1993
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Ingår i: ASME-Fluid Engineering Conference, Washington DC.
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Konferensbidrag (refereegranskat)abstract
- Measurements of the Reynolds stress tensor have been carried out in a complex three-dimensional boundary layer using different techniques. Single-, cross- and three-hot-wire probes were employed together with a silicon based double chip sensor. All measurements were performed at a Reynolds number of 1.2 x ___ per meter. The turbulent stresses were determined at a reference position in a two-dimensional part of the flow field and at three locations with different strength of the three-dimensionality. A good agreement was found in the turbulent quantities measured with the different methods, however, the influence of prong interference, measuring volumes and velocity gradients were noted.
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| 3. |
- Löfdahl, Lennart, 1948, et al.
(författare)
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Measurement of the Enstrophy and the Vorticity Vector in a Plane Cylinder Wake using a Spectral Method
- 1994
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Ingår i: Fifth European Turbulence Conference in Siena, Italy, July 5-8 1994..
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Konferensbidrag (refereegranskat)abstract
- A method to determine derivative moments using only two slanted hot-wires and a spectral method has been employed for a complete determination of the enstrophy and the vorticity vector. The general idea behind the method is to minimize the measuring volume by use of only two hot-wires and to post-process the measured data. All measurements were conducted in the far wake of a cylinder at a Reynolds number of 1840. Comparisons between the spectral method and conventional measuring techniques are made, and the results justifies the approximation between enstrophy and dissipation. For the vorticity vector it was found that the components of the normal and lateral directions were considerably larger than the stream-wise ones.
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| 4. |
- Abrahamsson, Hans, 1966, et al.
(författare)
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A Turbulent Plane 2-Dimensional Wall-Jet in a Quiescent Surrounding
- 1994
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Ingår i: European Journal of Mechanics/B-Fluids. - 0997-7546 .- 1873-7390. ; 13:5, s. 533-556
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Tidskriftsartikel (refereegranskat)abstract
- An experimental investigation of the turbulence field in a plane two-dimensional wall-jet has been conducted. All measurements were carried out employing hot-wire techniques in a large scale experimental facility. Mean velocities, Reynolds stresses and wall shear stress were determined with slot Reynolds numbers of 1.0*104, 1.5*104 and 2.0*104. The wall-jet was found to be self-preserving, and an asymptotic scale matching was used to show the existence of a short inertial sub layer as compared with a wall boundary layer. Studies of the integral scale development and the turbulent diffusion of shear stress showed a strong interaction between the inner and outer regions of the wall-jet. Using momentum scaling, it was found that the streamwise development of the half-width and maximum mean velocity was independent of the slot Reynolds number.
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| 5. |
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| 6. |
- Abrahamsson, Hans, 1966, et al.
(författare)
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Turbulence in a Two-Dimensional Wall-Jet - Experiments and Modeling
- 1992
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Ingår i: 13th Turbulence Conference in Missouri-Rolla..
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Konferensbidrag (refereegranskat)abstract
- An experimental and numerical investigation of the turbulence field in a two-dimensional wall-jet has been carried out in a well-defined geometry. The measurements were performed using a hot-wire technique and the calculations were carried out with a standard k-ε model as well as an algebraic stress model (ASM), using elliptic solvers. For the mean velocity field, good agreements were found between the measurements and the calculations. The measurements of the turbulence intensities reveal two maxima in the stream-wise and span-wise components, while only one maximum was found in the normal component. Also in the shear stress two maxima were found. A comparison between calculations and measurements indicates that improved turbulence models are needed.
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| 7. |
- Abrahamsson, Hans, 1966, et al.
(författare)
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Turbulence Measurements in a Two-Dimensional Wall-Jet
- 1991
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Ingår i: Eight Turbulent Shear Flow Conference, München.
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Konferensbidrag (refereegranskat)abstract
- The high capacity of todays computers has enabled the extension of turbulence models to strongly anisotropic flow fields, i.e. the interest has been focused on the use of the models based on the transport equations for the Reynolds stresses (RST models). To improve these turbulence models well-defined, simple and fundamental experiments are needed, in which gradients of the different turbulence parameters are determined. Together with direct simulations of the Navier-Stokes equations these experiments yield a good base for the improvement of the modelling of different terms in the Reynolds equations. An excellent presentation of the closure problem and the terms of interest for the development of turbulence models has recently been published by Groth (1991). A fundamental, well-defined and simple flow case is the wall-jet, where an interaction between a wall boundary layer and a free shear layer forms the anisotropy as well as the inhomogeneous character of the flow field. A comprehensive literature survey of wall-jets was carried out already in the beginning of the eighties by Launder and Rodi (1980), who studied a large number of more or less well-defined wall-jet experiments. The main conclusion of this survey was a lack of well-defined experiments in simple and fundamental geometries. If the study is limited to the two-dimensional case, a further conclusion from the work of Launder and Rodi was that many of the studied flow cases did not fulfil the condition of two-dimensionality. Although more than ten years have passed since the work of Laundry and Rodi was presented, very few investigations have been reported in which fundamental wall-jets have been studied. Especially well-defined turbulence measurements are needed, since anisotropy of the two-dimensional wall-jet yields a case well suited for the evaluation of e.g. new dissipation models, see Hallbäck et al. (1990). The purpose of the present work was to determine the turbulence field of a two-dimensional wall-jet in a simple and also well-defined geometry without influence of an outer disturbing flow field. To accomplish these measurements was a wall-jet rig used. All turbulence measurements were carried out using hot-wire techniques, single- and cross wires. The measurements presented here were performed at a Reynolds number of ___, based on the slot height and the extensions of the measurements in the flow direction was in the range of x/h=25 through x/h=156 (x-coordinate in the main flow direction and h-slot height).
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| 8. |
- Andersson, Helge, 1950, et al.
(författare)
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Turbulence in the Vicinity of a Rotating Cylinder in a Quiescent Fluid
- 1991
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Ingår i: Eight Turbulence Shear Flow Conference, Munchen.
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Konferensbidrag (refereegranskat)abstract
- An experimental and numerical investigation of the turbulence field in the vicinity of a rotating cylinder in a quiescent fluid has been carried out. Radial distributions of mean velocity and non-vanishing Reynolds stress components have been measured using hot-wire technique, and corresponding components have been calculated with a low-Reynolds number second- moment closure model. From the measurements it can be concluded the turbulence field is established in the present set up at a Reynolds number which is roughly twenty times larger than earlier measurements have shown. Comparisons between calculations and measurements yield some deviations. However, a qualitatively good agreement is obtained. In the paper, different methods for the determination of the friction velocity are also described and discussed.
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| 9. |
- Eriksson, Martin, 1968, et al.
(författare)
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Flow Visualization and Turbulence Measurements in a Three-Dimensional Turbulence Wall Jet
- 1991
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Ingår i: First European Fluid Mechanics Conference in Cambridge September 16-20.
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Konferensbidrag (refereegranskat)abstract
- The modelling of turbulence has recently been directed towards the handling of anisotropic flow fiends, i.e. the interest has been focused on the use of models base on the transport equations for the Reynolds stresses (RST models). To improve these turbulence models well-defined, simple and fundamental experiments are needed in which gradients of the different turbulence parameters are determined. Together with direct simulations of the Navier-Strokes equations these experiments yield a good base for the improvement of different terms in the Reynolds equations.A fundamental, well-defined and simple flow case is the three-dimensional wall jet, where an interaction between a wall boundary layer and a free shear layer forms the anisotropy as well as the inhomogeneous character of the flow field.The purpose of the present work was to study the turbulence field of a three-dimensional wall jet, without an outer disturbing flow field. This was accomplisher by using smoke visualization and hot-wire technique for mean velocity and turbulence measurements. In the present measurement a Reynolds number104 was used, and the extension of the measurements in the flow direction was in the range x/h = 25 through x/h = 62 (x – coordinate in the flow direction and h – slot height.) Preston tubes were employed for the determination of friction of the friction velocity.The spreading rates in the normal as well as lateral direction were visualized for a rectangular and a circular orifice. Different sizes of the vertical wall perpendicular to the outlet were also tested. All spreading rates were determined for the outer boundary of the smoke plumes. It was found that the normal spreading rate was influenced by the wall size as well as the orifice geometry. High wall and circular orifice implied a reduction of the normal spreading. In the lateral direction, no significant difference could be noticed due to either wall size or orifice geometry.Profiles of mean velocities and turbulent quantities were determined at five positions on the centre-line. At three of these positions, equally spaced, the mean velocity and turbulence intensity were also determined at positions off the centre-line to enable the determination of the lateral spreading. From the measurements the normal spreading rate, based as usually on the half-width, was determined to 0.055 and the lateral spreading was estimated in the same way to 0.27. Considering the turbulence measurements, the typical two-point maxima can be found in the normal stress component. A comparison of the profiles for different orifice geometry yields that the orifice not seems to have any significant influence on the turbulence intensity. From the off centre-line measurements it can be noted that the profile shape is approximately the same as on the centre-line.Cross-wire technique was employed for the determination of shear stress profiles along the centre-line.
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| 10. |
- Löfdahl, Lennart, 1948, et al.
(författare)
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A Fast Simple Hot-Wire Method of Determining the Mean Velocity Vector of Complex Three-Dimensional Flows
- 1996
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Ingår i: Experiments in Fluids. ; 20, s. 398-400
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Tidskriftsartikel (refereegranskat)abstract
- A fast and simple method of determining the mean velocity vector of complex three-dimensional flow fields is outlined. Straight and slanted single hot-wires are rotated in two perpendicular planes. This method increases the angular resolution, which is of importance in flow situations where one of the velocity components dominates and the other changes rapidly from one point to another. The method was calibrated in a wind tunnel and assessed in the internal flow field at the outlet of a fan in a defroster channel. It is shown that the hot-wire method yields good agreement with corresponding flow visualizations determined using a textile thread, and an integration of the measured mean flow yields a flow rate which agrees within a few percent with corresponding direct measurements on an orifice plate.
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