Gary J. Kunkel

Streamwise turbulence intensity formulation for flat-plate boundary layers

A similarity formulation is proposed to describe the streamwise turbulence intensity across the entire smooth-wall zero-pressure-gradient turbulent boundary layer. The formulation is an extension of the Marusic, Uddin, and Perry [Phys. Fluids 9, 3718 (1997)] formulation that was restricted to the outer region of the boundary layer, including the logarithmic region. The new formulation is found to agree very well with experimental data over a large range of Reynolds numbers varying from laboratory to atmospheric flows. The formulation is founded on physical arguments based on the attached eddy hypothesis, and suggests that the boundary layer changes significantly with Reynolds number, with an outer flow influence felt all the way down to the viscous sublayer. The formulation may also be used to explain why the empirical mixed scaling of DeGraaff and Eaton [J. Fluid Mech. 422, 319 (2000)] appears to work.

Study of the near-wall-turbulent region of the high-Reynolds-number boundary layer using an atmospheric flow

(Received 31 March 2005 and in revised form 29 July 2005) Data from the near-wall-turbulent region of the high-Reynolds-number atmospheric surface layer are used to analyse the attached-eddy model of wall turbulence. All data were acquired during near-neutral conditions at the Surface Layer Turbulence and Environmental Science Test (SLTEST) facility located in the western Utah Great Salt Lake Desert. Instantaneous streamwise and wall-normal components of velocity were collected with a wall-normal array of two-component hot wires within the first 2 m above the surface of the salt flats. Streamwise and wall-normal turbulence intensities and spectra are directly compared to corresponding laboratory data and similarity formulations hypothesized from the attached-eddy model of wall turbulence. This affords the opportunity to compare results with Reynolds numbers varying over three orders of magnitude. The wall-normal turbulence-intensity similarity formulation is extended. The results show good support for the similarity arguments forwarded by the attached-eddy model as well as Townsend’s (1956) Reynolds-number similarity hypothesis and lack of the ‘inactive’ motion influence on the wall-normal velocity component. The effects of wall roughness and the spread in the convection velocity due to this roughness are also discussed. An experimental investigation of the near-wall-turbulent (logarithmic) region of the high-Reynolds-number turbulent boundary layer was conducted. The main purpose of this work is to use these data to investigate the attached-eddy model of wallbounded turbulence at high Reynolds numbers. (A good review of the importance of understanding high-Reynolds-number wall-bounded flow is given by Gad-el-Hak & Bandyopadhyay 1994.) The attached-eddy model essentially provides a kinematic description for wall-bounded turbulence. The foundation of the model, which is based on the attached-eddy hypothesis of Townsend (1976), is the observation that wallbounded turbulence contains a collection of coherent structures or eddies. Therefore, the model proposes that the statistical features of wall-bounded turbulence can be modelled by a linear superposition of such eddies. The model has been refined and developed over the past three decades on the data of low-to-moderate Reynoldsnumber wall-bounded turbulence experiments (e.g. pipe and boundary-layer flow) and has led to a number of similarity laws. For a complete review of the attached-eddy model see Perry & Marusic (1995) and the references therein.

Turbulence measurements using a nanoscale thermal anemometry probe

A nanoscale thermal anemometry probe (NSTAP) has been developed to measure velocity fluctuations at ultra-small scales. The sensing element is a free-standing platinum nanoscale wire, 100 nm × 2 µm × 60 µm, suspended between two currentcarrying contacts and the sensor is an order of magnitude smaller than presently available commercial hot wires. The probe is constructed using standard semiconductor and MEMS manufacturing methods, which enables many probes to be manufactured simultaneously. Measurements were performed in grid-generated turbulence and compared to conventional hot-wire probes with a range of sensor lengths. The results demonstrate that the NSTAP behaves similarly to conventional hot-wire probes but with better spatial resolution and faster temporal response. The results are used to investigate spatial filtering effects, including the impact of spatial filtering on the probability density of velocity and velocity increment statistics.

Experimental study of wall boundary conditions for Large Eddy Simulation

Copyright 2001 Cambridge University Press. Marusic, Ivan and Kunkel, Gary J and Porte-Agel, Fernando (2001) Experimental study of wall boundary conditions for large-eddy simulation. Journal of Fluid Mechanics 446:pp. 309-320. http://www.jfm.damtp.cam.ac.uk/

Flow in a commercial steel pipe

The overall objective of this work was to improve the one-dimensional models used to simulate the transport of single-phase natural gas in Norway’s large-diameter export pipelines. There was a particular focus on the simulator used by the state-owned company Gassco named Transient Gas Network (TGNet). This simulator was studied in order to uncover any weaknesses or inaccuracies and to predict the natural gas transport with better accuracy both in the daily operation and when long-term capacity calculations are made. The conclusion was that the simulator in general resolves the physics well, provided that the input correlations such as viscosity correlation and friction factor correlation are accurate. The simulator was therefore found trustworthy to be used in the determination of the friction factor for operational data. No satisfactory correlations exist for the additional pressure loss in smooth curves, and like all other commercial simulators TGNet ends up modeling only a straight pipe. This is a weakness, but the magnitude of the associated error is unknown. The simulator also fails to predict the heat transfer for partly buried pipelines. The sensitivity analysis performed on an artificial pipeline model as well as the uncertainty analysis for the full-scale experiments both indicated which parameters are most important in the simulations: • Gas density calculations • Ambient temperature (affecting the gas temperature) • Flow rate measurements • Inner diameter of pipeline The fricton factor was analyzed both by means of laboratory experiments in the high Reynolds number facility Superpipe at Princeton University in US and by comprehensive analysis of real operational data at the largest Reynolds numbers ever covered. The Superpipe measurements were made on a 5 inch inner diameter natural rough steel pipe, and covered both the smooth, transitionally rough and the fully rough region. Reynolds numbers from 150·103 to 20·106 were covered. Due to lack of studies on naturally rough surfaces in literature, these measurements yielded very interesting results. The transition zone was abrupt, but was neither a point transition nor an inflectional transition. The equivalent sand grain roughness was furthermore found to be 1.6 times the measured root mean square roughness, which is in contrast to the value of 3.0 to 5.0 that is commonly used. Operational data were collected from two full-scale steel pipelines with an inner diameter of 40 and 42 inches respectively, covering Reynolds numbers from 10·106 to 45·106 . The experiments showed friction factors signicantly lower than predicted by the Colebrook-White correlation and based on reported roughness measurements. It was also concluded that the pipelines are in the transition zone which is more abrupt than that of Colebrook-White. Increased knowledge about the frictional pressure drop at large flow rates resulting from analysis of operational data has led to updated and increased capacity calculations in several pipelines. The increase is in the range 0.2-1.0%, and facilitates an improved utilization of the natural gas transport infrastructure on the Norwegian Continental Shelf. This work includes three different papers, one presented at an international conference and two published in peer-reviewed international journals.

Further support for Townsend’s Reynolds number similarity hypothesis in high Reynolds number rough-wall pipe flow

Measurements of turbulence behavior in high Reynolds number fully developed rough-wall pipe flow are presented. The data are acquired with single-component conventional hot-wire anemometry in the Princeton/ONR Superpipe fitted with a honed rough pipe. Streamwise turbulence intensities, higher-order moments, and spectra are compared with the corresponding results from a previous smooth-wall pipe flow study in the same facility. Accepting the experimental challenges of conducting hot-wire anemometry studies in such a facility, the rough-wall data agree well with the smooth-wall data in the outer region of the flow, strongly supporting Townsend’s Reynolds number similarity hypothesis.

Development of NSTAP: Nanoscale Thermal Anemometry Probe

A nanoscale thermal anemometry probe (NSTAP) has been developed to measure instantaneous ∞uid velocity at ultra-small scales. The sensing length of the current probe (»60 „m) is and order of magnitude smaller than presently available commercial hot-wire anemometer probes (TSI Inc, Dantec Inc). The sensing element is a freestanding nanowire 100 nm £ 1„m £ 60 „m suspended between two current-carrying contacts. The probe is constructed using standard semiconductor and microelectromechanical systems manufacturing methods. The increased surface area to volume ratio of the metallic nanowire in comparison to conventional probes yields a device that not only has a higher spatial resolution but is also more sensitive and rapid in its response to changing ∞ows.

Turbulence Intensity Similarity Laws For Turbulent Boundary Layers

Turbulence intensity similarity laws, which are based on the attached eddy hypothesis, are tested with new high Reynolds number data obtained in the atmospheric surface layer. The existing formulation for the streamwise component was until now restricted to the log region and above. A new extended version is proposed that applies across the entire boundary layer for smooth wall flows and explains why the near- wall mixed scaling proposed by DeGraaff and Eaton, 2000 appears to be successful.

Turbulence characteristics in high-Reynolds-number rough-wall pipe ∞ow

Measurements of turbulence behavior in high-Reynolds-number fully-developed roughwall pipe ∞ow are presented. The data are acquired with conventional hot-wire anemometry in the Princeton/ONR Superpipe, which has recently been fltted with a honed rough pipe. Turbulence intensities, higher order moments, and spectra are compared with the corresponding results from an earlier smooth-wall pipe ∞ow study in the same facility. Accepting the experimental challenges of conducting hot-wire anemometry studies in such a facility, the rough-wall data agrees with the smooth-wall data in all statistics analyzed here.

SIMILARITY FORMULATIONS FOR TURBULENT BOUNDARY LAYERS AT HIGH REYNOLDS NUMBERS

Data obtained from the high Reynolds number atmospheric boundary layer are used to analyze existing mean-flow and turbulence intensity similarity formulations. From the results of this analysis a new streamwise turbulence intensity formulation is proposed that is suggested to be applicable across the entire smooth-wall high Reynolds number turbulent boundary layer. The new formulation is also shown to be consistent with the mixed-flow scaling suggested by other studies.