Turbulent Flow Over a Flat Plate Downstream of a Finite Height Perforated Plate

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
F. Fouladi ◽  
P. Henshaw ◽  
D. S.-K. Ting
Keyword(s):  
Turbulent Flow ◽  
Flat Plate ◽  
Short Distance ◽  
Free Stream ◽  
Perforated Plate ◽  
Leading Edge ◽  
Grid Turbulence ◽  
Hot Wire ◽  
Velocity Measurements ◽  
Finite Height

An experimental investigation was carried out to study the turbulent flow over a flat plate in a wind tunnel. The turbulence was generated by a plate with diamond-shaped perforations mounted perpendicular to and on the leading edge of the flat plate. Unlike conventional grid turbulence studies, this perforated plate had a finite height, and this height was explored as a key independent parameter. Instantaneous velocity measurements were performed with a 1D hot-wire anemometer to reveal the behavior of the flow a short distance downstream of the perforated plate (X/D = 10–30). Different perforated plate heights (H = 3, 7, 11 cm) and free stream velocities (U = 4.5, 5.5, 6.5 m/s) have been studied.

scholarly journals Measurements of Unsteady Flow Over and Heat Transfer From a Flat Plate

1989 ◽  
Author(s):  
X. Liu ◽  
W. Rodi
Keyword(s):  
Heat Transfer ◽  
Unsteady Flow ◽  
Flat Plate ◽  
Free Stream ◽  
Hot Wire ◽  
Velocity Measurements ◽  
Squirrel Cage ◽  
Plate Velocity ◽  
Flow Processes ◽  
Hot Film

A detailed experimental investigation is described of unsteady flow over and heat transfer from a flat plate. The oncoming 2-D periodic unsteady flow was generated by a squirrel cage device mounted upstream of the plate. Velocity measurements were carried out in the free stream over the plate and in the boundary layer by hot-wire anemometers, and the distributions of pressure and heat transfer coefficient along the plate surface were measured, the latter with a glue-on hot film. All results are presented in ensemble averaged form so that the unsteady flow processes can be studied phase by phase.

scholarly journals A Theory for Wake-Induced Transition

1989 ◽  
Author(s):  
R. E. Mayle ◽  
K. Dullenkopf
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Flow ◽  
Flat Plate ◽  
Free Stream ◽  
Plate Boundary ◽  
Transition Model ◽  
Model Comparisons ◽  
Turbulent Wakes ◽  
Flat Plate Boundary Layer

A theory for transition from laminar to turbulent flow as the result of unsteady, periodic passing of turbulent wakes in the free stream is developed using Emmons’ transition model. Comparisons made to flat plate boundary layer measurements and airfoil heat transfer measurements confirm the theory.

The Evolution of Streamwise Counter-Rotating Vortices in Flat Plate Boundary Layer With Leading Edge Pattern

2015 ◽  
Author(s):  
Seyed Mohammad Hasheminejad ◽  
Hatsari Mitsudharmadi ◽  
S. H. Winoto ◽  
Kim Boon Lua ◽  
Hong Tong Low
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Plate Boundary ◽  
Leading Edge ◽  
Streamwise Vortex ◽  
Streamwise Velocity ◽  
Stream Velocity ◽  
Hot Wire ◽  
Layer Flow ◽  
Different Characteristics

The evolution of streamwise counter-rotating vortices induced by different leading edge patterns is investigated quantitatively using hot-wire anemometer. A notched and triangular leading edge with the same wavelength and amplitude were designed to induce streamwise vortices over a flat plate at Reynolds number (based on the wavelength of the leading edge patterns) of 3080 corresponding to free-stream velocity of 3 m/s. The streamwise velocity at different streamwise locations collected and analyzed using a single wire probe hot-wire anemometer showed reveal different characteristics of boundary layer flow due to the presence of these two leading edge patterns. The major difference is the appearance of an additional streamwise vortex between the troughs of the notched pattern. Such vortices increase the mixing effect in the boundary layer as well as the velocity profile.

Measurements with a pulsed-wire and a hot-wire anemometer in the highly turbulent wake of a normal flat plate

1976 ◽  
Vol 77 (3) ◽  
pp. 473-497 ◽  
Author(s):  
L. J. S. Bradbury
Keyword(s):  
Turbulent Flow ◽  
Flat Plate ◽  
Flow Direction ◽  
Operating Conditions ◽  
Turbulent Intensity ◽  
Hot Wire ◽  
Mean Flow ◽  
Mean Velocity ◽  
The Mean ◽  
Better Than

This paper describes an investigation into the response of both the pulsed-wire anemometer and the hot-wire anemometer in a highly turbulent flow. The first part of the paper is concerned with a theoretical study of some aspects of the response of these instruments in a highly turbulent flow. It is shown that, under normal operating conditions, the pulsed-wire anemometer should give mean velocity and longitudinal turbulent intensity estimates to an accuracy of better than 10% without any restriction on turbulence level. However, to attain this accuracy in measurements of turbulent intensities normal to the mean flow direction, there is a lower limit on the turbulent intensity of about 50%. An analysis is then carried out of the behaviour of the hot-wire anemometer in a highly turbulent flow. It is found that the large errors that are known to develop are very sensitive to the precise structure of the turbulence, so that even qualitative use of hot-wire data in such flows is not feasible. Some brief comments on the possibility of improving the accuracy of the hot-wire anemometer are then given.The second half of the paper describes some comparative measurements in the highly turbulent flow immediately downstream of a normal flat plate. It is shown that, although it is not possible to interpret the hot-wire results on their own, it is possible to calculate the hot-wire response with a surprising degree of accuracy using the results from the pulsed-wire anemometer. This provides a rather indirect but none the less welcome check on the accuracy of the pulsed-wire results, which, in this very highly turbulent flow, have a certain interest in their own right.

Improvement of Constant Temperature Anemometer and Measurement of Energy Spectra in a Plane Turbulent Jet

2012 ◽  
Author(s):  
Osamu Terashima ◽  
Kazuhiro Onishi ◽  
Yasuhiko Sakai ◽  
Kouji Nagata
Keyword(s):  
Frequency Response ◽  
Free Stream ◽  
Wheatstone Bridge ◽  
Wave Number ◽  
Stream Velocity ◽  
Fine Scale ◽  
Hot Wire ◽  
Velocity Measurements ◽  
Scale Structures ◽  
Constant Temperature Anemometer

A constant temperature anemometer (CTA) is a useful instrument for measuring the velocity fluctuations in turbulent flow. However, in our calibration test, the actual frequency response of a typical CTA was no more than 5 kHz under normal laboratory conditions: for example, the diameter of the hot wire is 5 μm and the free stream velocity is 20 m/s. Therefore, in some cases, a typical CTA is not enough to measure accurately turbulent velocity fluctuations for fine scale structures. In this paper, we present a rearranged CTA circuit to obtain a faster frequency response so that in turn fine-scale structures can be more accurately investigated. A typical CTA circuit consists of a Wheatstone bridge and a feed back circuit. To improve the frequency response, the ratio of the electrical resistance of the Wheatstone bridge is set to 1 and two operational amplifiers with a gain-band width product of 100 MHz and a slew rate of 20 V/μs are used in the feedback circuit. An experiment to estimate the frequency response of the rearranged CTA circuit is performed with a free stream velocity of 20 m/s and using hot wires of diameter 5 μm and 3 μm. Experimental results show that the roll-off frequency of the rearranged CTA circuit is improved from 5 kHz to 20 kHz for the 5 μm hot wire and from 6 kHz to 40 kHz for the 3 μm hot wire. Velocity measurements are made using the rearranged CTA circuit in a plane turbulent jet where the value of the Taylor microscale λ is 3.2 mm and the Taylor-scale Reynolds number Reλ is 440. Measurements shows that the power spectrum obeys the reliable numerical profile derived by a LDIA (Lagrangian Direct-Interaction Approximation) theory until more than 0.20 of the non-dimensional wave number κ1η, which is a wider range in comparison with the results obtained when using a typical CTA circuit. Here, κ1 is the axial wave number and η is the Kolmogorov microscale. Further, velocity measurements are performed taken using the rearranged CTA circuit with a square jet where the value of λ is 6.3 mm and Reλ is 1,720. Measurements shows that the power spectrum obeys the numerical profile by the LDIA theory in the range 0.04 < κ1η < 0.20, which is a much wider range than the results obtained when using a typical CTA circuit (0.04 < κ1η < 0.08). These results indicate that the rearranged CTA circuit can be used to investigate fine-scale structures in turbulent flows more accurately.

Receptivity to free-stream vorticity of flow past a flat plate with elliptic leading edge

2010 ◽  
Vol 653 ◽  
pp. 245-271 ◽  
Author(s):  
L.-U. SCHRADER ◽  
L. BRANDT ◽  
C. MAVRIPLIS ◽  
D. S. HENNINGSON
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Free Stream ◽  
Three Dimensional ◽  
Low Frequency ◽  
Leading Edge ◽  
Sound Waves ◽  
Streamwise Vorticity ◽  
Low Frequencies ◽  
Free Stream Turbulence

Receptivity of the two-dimensional boundary layer on a flat plate with elliptic leading edge is studied by numerical simulation. Vortical perturbations in the oncoming free stream are considered, impinging on two leading edges with different aspect ratio to identify the effect of bluntness. The relevance of the three vorticity components of natural free-stream turbulence is illuminated by considering axial, vertical and spanwise vorticity separately at different angular frequencies. The boundary layer is most receptive to zero-frequency axial vorticity, triggering a streaky pattern of alternating positive and negative streamwise disturbance velocity. This is in line with earlier numerical studies on non-modal growth of elongated structures in the Blasius boundary layer. We find that the effect of leading-edge bluntness is insignificant for axial free-stream vortices alone. On the other hand, vertical free-stream vorticity is also able to excite non-modal instability in particular at zero and low frequencies. This mechanism relies on the generation of streamwise vorticity through stretching and tilting of the vertical vortex columns at the leading edge and is significantly stronger when the leading edge is blunt. It can thus be concluded that the non-modal boundary-layer response to a free-stream turbulence field with three-dimensional vorticity is enhanced in the presence of a blunt leading edge. At high frequencies of the disturbances the boundary layer becomes receptive to spanwise free-stream vorticity, triggering Tollmien–Schlichting (T-S) modes and receptivity increases with leading-edge bluntness. The receptivity coefficients to free-stream vortices are found to be about 15% of those to sound waves reported in the literature. For the boundary layers and free-stream perturbations considered, the amplitude of the T-S waves remains small compared with the low-frequency streak amplitudes.

Measurements of the velocity field of a wing-tip vortex, wandering in grid turbulence

2008 ◽  
Vol 601 ◽  
pp. 281-315 ◽  
Author(s):  
S. C. C. BAILEY ◽  
S. TAVOULARIS
Keyword(s):  
Free Stream ◽  
Tip Vortex ◽  
Grid Turbulence ◽  
Velocity Measurements ◽  
Free Stream Turbulence ◽  
Normal Probability ◽  
Rate Of Decay ◽  
Wing Tip Vortex ◽  
Point Velocity ◽  
Wing Tip

Velocity measurements were performed in a wing-tip vortex wandering in free-stream turbulence using two four-wire hot-wire probes. Vortex wandering was well represented by a bi-normal probability density with increasing free-stream turbulence resulting in increased amplitude of wandering. The most dominant wavelength of wandering was found to remain unaffected by free-stream conditions. Two-point velocity measurements were used to reconstruct the vortex velocity profile in a frame of reference wandering with the vortex. Increasing turbulence intensity was found to increase the rate of decay of the vortex peak circumferential velocity while the radial location of this peak velocity remained unchanged. These results are consistent with several possible vortex decay mechanisms, including the stripping of vorticity by azimuthally aligned vortical structures, transfer of angular momentum from the vortex to these structures during their formation and the deformation and breakup of the vortex by strong free-stream eddies.

Experiments on transitional boundary layers with wake-induced unsteadiness

1991 ◽  
Vol 231 ◽  
pp. 229-256 ◽  
Author(s):  
X. Liu ◽  
W. Rodi
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Free Stream ◽  
Leading Edge ◽  
Clear Correlation ◽  
Hot Wire ◽  
Test Plate ◽  
Streamwise Location ◽  
Boundary Layer Development ◽  
Wake Passing

Hot-wire measurements were carried out in boundary layers developing along a flat plate over which wakes passed periodically. The wakes were generated by cylinders moving on a squirrel cage in front of the plate leading edge. The flow situation studied is an idealization of that occurring on turbomachinery blades where unsteady wakes are generated by the preceding row of blades. The influence of wake-passing frequency on the boundary-layer development and in particular on the transition processes was examined. The hot-wire signals were processed to yield ensemble-average values and the fluctuations could be separated into periodic and stochastic turbulent components. Hot-wire traces are reported as well as time variations of periodic and ensemble-averaged turbulent fluctuations and of the boundary-layer integral parameters, yielding a detailed picture of the flow development. The Reynolds number was relatively low so that in the limiting case of a boundary layer undisturbed by wakes this remained laminar over the full length of the test plate. When wakes passed over the plate, the boundary layer was found to be turbulent quite early underneath the free-stream disturbances due to the wakes, while it remained initially laminar underneath the undisturbed free-stream regions in between. The turbulent boundary-layer stripes underneath the disturbed free stream travel downstream and grow together so that the embedded laminar regions disappear and the boundary layer becomes fully turbulent. The streamwise location where this happens moves upstream with increasing wake-passing frequency, and a clear correlation could be determined in the experiments. The results are also reported in a mean Lagrangian frame by following fluid parcels underneath the disturbed and undisturbed free stream, respectively, as they travel downstream.

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