Near Wall Measurements for a Turbulent Impinging Slot Jet (Data Bank Contribution)1

2000 ◽  
Vol 123 (1) ◽  
pp. 112-120 ◽  
Author(s):  
Jiang Zhe ◽  
Vijay Modi
Keyword(s):  
Target Surface ◽  
Data Bank ◽  
Reynolds Numbers ◽  
Viscous Sublayer ◽  
Hot Wire ◽  
Velocity Measurements ◽  
Mean Velocity ◽  
Stagnation Region ◽  
Impingement Plate ◽  
Linear Behavior

The velocity field in the vicinity of a target surface with a turbulent slot jet impinging normally on it is examined. The impingement region is confined by means of a confinement plate that is flush with the slot and parallel to the impingement plate. The distance H of the impingement wall from the slot is varied from 2 to 9.2 slot widths. Jet Reynolds numbers (based on slot width B) of 10,000–30,000 are considered. Mean velocity and root mean square velocity measurements are carried out using hot-wire anemometry. A boundary layer probe is utilized in order to obtain measurements at a wall distance as close as 110 microns 0.0028B. This corresponds to a distance of approximately y+∼2-4 in wall units and is found to be adequate in order to permit an estimate of wall shear under most conditions. The problems of hot wire interference with the wall and calibration at low velocities are solved by calibrating the probe in a known Blasius flow. With the exception of the stagnation region where shear could not be evaluated, it is found that velocity profiles follow a linear behavior in the viscous sublayer everywhere along the wall. Results indicate that the peak in normal stress occurs at y/B∼0.025 to 0.04 at a distance six to eight jet widths away from the jet-axis.

scholarly journals Obtaining accurate mean velocity measurements in high Reynolds number turbulent boundary layers using Pitot tubes

2013 ◽  
Vol 715 ◽  
pp. 642-670 ◽  
Author(s):  
S. C. C. Bailey ◽  
M. Hultmark ◽  
J. P. Monty ◽  
P. H. Alfredsson ◽  
M. S. Chong ◽  
...  
Keyword(s):  
Plate Boundary ◽  
Reynolds Numbers ◽  
Velocity Shear ◽  
Hot Wire ◽  
Velocity Measurements ◽  
Mean Velocity ◽  
Close Proximity ◽  
High Reynolds ◽  
Different Diameters ◽  
Comparable Magnitude

AbstractThis article reports on one component of a larger study on measurement of the zero-pressure-gradient turbulent flat plate boundary layer, in which a detailed investigation was conducted of the suite of corrections required for mean velocity measurements performed using Pitot tubes. In particular, the corrections for velocity shear across the tube and for blockage effects which occur when the tube is in close proximity to the wall were investigated using measurements from Pitot tubes of five different diameters, in two different facilities, and at five different Reynolds numbers ranging from ${\mathit{Re}}_{\theta } = 11\hspace{0.167em} 100$ to 67 000. Only small differences were found amongst commonly used corrections for velocity shear, but improvements were found for existing near-wall proximity corrections. Corrections for the nonlinear averaging of the velocity fluctuations were also investigated, and the results compared to hot-wire data taken as part of the same measurement campaign. The streamwise turbulence-intensity correction was found to be of comparable magnitude to that of the shear correction, and found to bring the hot-wire and Pitot results into closer agreement when applied to the data, along with the other corrections discussed and refined here.

Time-Resolved Velocity Measurements in a Matched Refractive Index Facility of Randomly Packed Spheres

2018 ◽  
Author(s):  
Ethan Kappes ◽  
Mateusz Marciniak ◽  
Andrew Mills ◽  
Robert Muyshondt ◽  
Stephen King ◽  
...  
Keyword(s):  
Root Mean Square ◽  
Experimental Studies ◽  
Reynolds Numbers ◽  
Index Of Refraction ◽  
Mean Square ◽  
Reynolds Stresses ◽  
Velocity Measurements ◽  
Mean Velocity ◽  
Time Resolved ◽  
Wall Boundary

Complex geometries and randomly connected void spaces within packed beds have hindered efforts to characterize the underlying transport phenomena occurring within. In this communication, we present our experimental studies on a facility of randomly packed spheres that can be a representative of sections within a reactor core in a nuclear power plant. The results of high-fidelity velocity measurements can be seen using Time-Resolved Particle Image Velocimetry (TR-PIV) at the pore scales and near the wall boundary in the Matched Index of Refraction (MIR) facility. The MIR approach allows for a non-invasive analysis of the flow within packed spheres at the microscopic scales with high temporal and spatial resolution. Flow characteristics obtained from the TR-PIV measurements at various Reynolds numbers are presented. The results include the first- and second-order flow statistics, such as mean velocity, root-mean-square fluctuating velocity and Reynolds stresses. Effects of the wall boundary and Reynolds numbers on flow patterns are currently being investigated. Comparisons of the mean velocities, root-mean-square fluctuating velocities, and Reynolds stress components show the increase of flow mixing and turbulent intensities within the gaps between spheres in the packed bed. Sizes of recirculation regions, however, seem to be independent of the increase of Reynolds numbers.

A possible reinterpretation of the Princeton superpipe data

2001 ◽  
Vol 439 ◽  
pp. 395-401 ◽  
Author(s):  
A. E. PERRY ◽  
S. HAFEZ ◽  
M. S. CHONG
Keyword(s):  
Boundary Layer ◽  
Reynolds Numbers ◽  
Additive Constant ◽  
Velocity Data ◽  
Hot Wire ◽  
Mean Velocity ◽  
Displacement Effect ◽  
Law Of The Wall ◽  
Hot Wires ◽  
Logarithmic Law

In experiments recently performed at Melbourne, Pitot-tube mean velocity profiles in a boundary layer disagreed with those obtained with hot wires. The standard MacMillan (1956) correction for the probe displacement effect and a correction for turbulence intensity were both required for obtaining agreement between the two sets of mean velocity data. We were thus motivated to reanalyse the Princeton superpipe data using the same two corrections. The result is a plausible conclusion that the superpipe is rough at the higher Reynolds numbers and its data follow the Colebrook (1939) formula for commercial pipes rather well. It also appears that the logarithmic law of the wall is valid, with a Kármán constant close to that found recently by Österlund (1999) from boundary layer measurements with a hot wire. The smooth regime in the pipe gave almost the same additive constant for the log-law as Österlund's. A comparison between the superpipe data and the pipe data of Perry, Henbest & Chong (1997) suggests that the conventional velocity defect law may be valid down to lower Reynolds numbers than concluded by Zagarola & Smits (1998).

Wake Flow Patterns Behind Rotating Smooth Spheres and Baseballs

2018 ◽  
Author(s):  
Patrick Mortimer ◽  
John C. Vaccaro ◽  
David M. Rooney
Keyword(s):  
Rotational Speed ◽  
Reynolds Numbers ◽  
Boundary Layer Separation ◽  
Wake Flow ◽  
Hot Wire ◽  
Mean Velocity ◽  
Magnus Effect ◽  
Power Spectral ◽  
The Mean ◽  
Smooth Sphere

An experimental investigation into the flow field behind baseballs at two different seam orientations as well as a smooth sphere of the same diameter was undertaken at Reynolds numbers of 5 × 104 and 1 × 105. The rotational speed of the three spheres varied from 0 to 2400 rpm, with data collected in increments of 400 rpm which correspond to relative spin rates between 0 and 0.94. Mean velocity profiles, turbulence in intensity profiles, and power spectral density of the signals were taken using hot-wire anemometry. The smooth sphere wake was seen to change in orientation over a range of relative rotational speeds. The Strouhal number remained constant around 0.24 for relatively low spin rates. The seams on the baseball suppressed any measurable vortex shedding once rotation began, also eliminating any significant change in wake orientation as evidenced by the mean velocity deficit and turbulence intensity profiles. It was concluded that the so-called inverse Magnus effect recorded by previous investigators at a specific Reynolds number / relative rotational speed of a sphere exists only for a smooth sphere and not for a sphere where the boundary layer separation is governed by raised seams.

Mist/Steam Heat Transfer in Confined Slot Jet Impingement

2000 ◽  
Vol 123 (1) ◽  
pp. 161-167 ◽  
Author(s):  
X. Li ◽  
J. L. Gaddis ◽  
T. Wang
Keyword(s):  
Heat Transfer ◽  
Stagnation Point ◽  
Jet Impingement ◽  
Target Surface ◽  
Future Generation ◽  
Reynolds Numbers ◽  
Heat Fluxes ◽  
Stagnation Region ◽  
Blade Cooling ◽  
Confined Channel

Internal mist/steam blade cooling technology has been considered for the future generation of Advanced Turbine Systems (ATS). Fine water droplets of about 5 μm were carried by steam through a single slot jet onto a heated target surface in a confined channel. Experiments covered Reynolds numbers from 7500 to 25,000 and heat fluxes from 3 to 21 kW/m2. The experimental results indicate that the cooling is enhanced significantly near the stagnation point by the mist, decreasing to a negligible level at a distance of six jet widths from the stagnation region. Up to 200 percent heat transfer enhancement at the stagnation point was achieved by injecting only ∼1.5 percent of mist. The investigation has focused on the effects of wall temperature, mist concentration, and Reynolds number.

Asymmetries in the wake of a submarine model in pitch

2015 ◽  
Vol 774 ◽  
pp. 416-442 ◽  
Author(s):  
A. Ashok ◽  
T. Van Buren ◽  
A. J. Smits
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Relative Strength ◽  
The Body ◽  
Wind Tunnels ◽  
Body Of Revolution ◽  
Streamwise Vortices ◽  
Velocity Measurements ◽  
Mean Velocity ◽  
High Angles Of Attack

Detailed velocity measurements in the wake of a body of revolution are reported for pitch angles up to $12^{\circ }$, over an unprecedented range of Reynolds numbers ($2.4\times 10^{6}\leqslant \mathit{Re}_{L}\leqslant 30\times 10^{6}$). The body of revolution, an idealized submarine shape (DARPA SUBOFF), is mounted using a support that mimics a semi-infinite sail. The wake measurements at all pitch angles and Reynolds numbers reveal the presence of a pair of streamwise vortices of unequal strengths which tend to rotate around each other as they evolve downstream. Various attempts to perturb the upstream conditions on the body had no significant impact on the relative strength of the vortices. In addition, two different models, tested in two different wind tunnels, show similar asymmetries, and we propose that wake asymmetry appears to be a robust feature of this flow, a result previously only seen for sharp-nosed bodies at high angles of attack. It is also shown that the wake behaviour for $x/D>5$, in terms of the streamwise mean velocity and turbulence intensity distributions, appears to become invariant with Reynolds number for $\mathit{Re}_{L}>4.8\times 10^{6}$.

scholarly journals Hot-wire investigation of the wake behind cylinders at low Reynolds numbers

1949 ◽  
Vol 198 (1053) ◽  
pp. 174-190 ◽  
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Reynolds Numbers ◽  
Sufficient Information ◽  
Hot Wire ◽  
Mean Velocity ◽  
Phase Measurements ◽  
Low Reynolds Numbers ◽  
Laminar Wake ◽  
Low Reynolds

The hot-wire technique has been used to measure the regular vortex street pattern behind a cylinder at low Reynolds number. Measurements of mean velocity distribution were made both below and above the critical Reynolds number at which the periodic motion appears. Amplitude and phase measurements gave sufficient information for computation of the instantaneous flow pattern of the vortex system. The important points resulting from the investigation are that (i) the critical Reynolds number at which vortices are shed is 40, (ii) in the range of Reynolds numbers investigated the vortices are not shed directly from the cylinder but appear some distance downstream as an instability of the laminar wake.

scholarly journals Hydraulic niche utilization by larvae of the three Drusinae clades (Insecta: Trichoptera)

Biologia ◽  
2020 ◽  
Author(s):  
Johann Waringer ◽  
Simon Vitecek ◽  
Jan Martini ◽  
Carina Zittra ◽  
Stephan Handschuh ◽  
...  
Keyword(s):  
Reynolds Numbers ◽  
Data Series ◽  
Confidence Limits ◽  
Velocity Measurements ◽  
Italian Alps ◽  
Mean Velocity ◽  
First Order ◽  
Upper Austria ◽  
Water Depths ◽  
Flow Velocities

AbstractHydraulic niche descriptors of final instar larvae of nine Drusus species (Trichoptera) were studied in small, spring-fed, first-order headwaters located in the Mühlviertel (Upper Austria), Koralpe (Carinthia, Austria), and in the Austrian and Italian Alps. The species investigated covered all three clades of Drusinae: the shredder clade (Drusus franzi, D. alpinus), the grazer clade (D. biguttatus, D. chauvinianus, D. dudor, D. monticola), and the filtering carnivore clade (D. chrysotus, D. katagelastos, D. muelleri). Flow velocity was measured at front center of 68 larvae, head upstream, on the top of mineral substrate particles at water depths of 10–30 mm, using a tripod-stabilized Micro propeller meter (propeller diameter = 10 mm). Each data series consisted of a sampled measurement lasting 30 s (measuring interval = 1 s). In total, 2040 single velocity measurements were taken. Instantaneous flow velocities and drag at the sites of the 68 larvae varied from 0 to 0.93 m s−1 and 0 to 8346 *10−6 N, respectively. Flow velocities and drag between the three clades were highly significantly different (p < 0.001); mean velocity (+ 95% confidence limits) for the three clades were 0.09 + 0.00 m s−1 for the shredder, 0.25 + 0.00 m s−1 for the grazer, and 0.31 + 0.01 m s−1 for the filtering carnivore clade; the corresponding data for drag were (85 + 18)*10−6 N, (422 + 61)*10−6 N and (1125 + 83)*10−6 N, respectively. Adhesive friction ranged from (41.07 + 53.03)*10−6 N in D. franzi to (255.24 + 216.87)*10−6 N in D. chrysotus. Except in D. franzi and D. dudor adhesive friction was always well below drag force, indicating that submerged weight alone was not sufficient to stabilize the larvae in their hydraulic environment. Reynolds numbers varied between 0 in D. franzi and D. alpinus, and 12,634 in D. katagelastos, with 7% of the total in the laminar (R < 500), 30% in the transitional (R = 500–2000), and 61% in the fully turbulent stage (R > 2000). Froude numbers (Fr) varied from 0 to 2.97. The two Drusus species of the shredder clade and three out of four species of the grazer clade were exposed to subcritical Fr < 1, one species of the grazer clade and two out of three species of the filtering clade to supercritical Froude numbers >1.

scholarly journals Preliminary Results of a Study of the Relationship Between Free Stream Turbulence and Stagnation Region Heat Transfer

1985 ◽  
Author(s):  
G. James VanFossen ◽  
Robert J. Simoneau
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Free Stream ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Nasa Lewis Research ◽  
Hot Wire ◽  
Stagnation Region ◽  
Stagnation Line ◽  
Free Stream Turbulence

A study is being conducted at the NASA Lewis Research Center to investigate the mechanism that causes free stream turbulence to increase heat transfer in the stagnation region of turbine vanes and blades. The work is being conducted in a wind tunnel at atmospheric conditions to facilitate measurements of turbulence and heat transfer. The model size is scaled up to simulate Reynolds numbers (based on leading edge diameter) that are to be expected on a turbine blade leading edge. Reynolds numbers from 13 000 to 177 000 were run in the present tests. Spanwise averaged heat transfer measurements with high and low turbulence have been made with “rough” and smooth surface stagnation regions. Results of these measurements show that the boundary layer remains laminar in character even in the presence of free stream turbulence at the Reynolds numbers tested. If roughness is added the boundary layer becomes transitional as evidenced by the heat transfer increase with increasing distance from the stagnation line. Hot wire measurements near the stagnation region downstream of an array of parallel wires has shown that vorticity in the form of mean velocity gradients is amplified as flow approaches the stagnation region. Circumferential traverses of a hot wire probe very near the surface of the cylinder have shown the fluctuating component of velocity changes in character depending on free stream turbulence and Reynolds number. Finally smoke wire flow visualization and liquid crystal surface heat transfer visualization have been combined to show that, in the wake of an array of parallel wires, heat transfer is a minimum in the wire wakes where the fluctuating component of velocity (local turbulence) was the highest. Heat transfer was found to be the highest between pairs of vortices where the induced velocity is toward the cylinder surface.

A Study of Incompressible Turbulent Boundary Layers in Channel Flow

1968 ◽  
Vol 90 (4) ◽  
pp. 455-467 ◽  
Author(s):  
J. A. Clark
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Viscous Sublayer ◽  
Turbulent Boundary Layers ◽  
Sufficient Accuracy ◽  
Hot Wire ◽  
Reasonable Estimate ◽  
Mean Velocity ◽  
Incompressible Turbulent Boundary Layer ◽  
The Mean

The fully developed incompressible turbulent boundary layer in a channel has been explored using constant-temperature hot-wire anemometry. Particular attention was paid to measurements well into the viscous sublayer, yielding results which are believed to be new. Frequency spectral analyses of the fluctuating velocity components have been obtained for the inner layers. The mean velocity distribution in the sublayer has been determined with sufficient accuracy for a reasonable estimate of skin friction to be made. The results are compared with those of Laufer [11] and Comte-Bellot [4].

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