Turbulent Mean-Flow Measurements in a Two-Dimensional Supersonic Wake

1969 ◽  
Vol 12 (1) ◽  
pp. 24 ◽  
Author(s):  
Anthony Demetriades
Keyword(s):  
Two Dimensional ◽  
Mean Flow ◽  
Flow Measurements ◽  
Supersonic Wake

M. J. Hartmann Memorial Session Paper: Turbulence Characteristics in a Supersonic Cascade Wake Flow

1994 ◽  
Vol 116 (4) ◽  
pp. 586-596 ◽  
Author(s):  
P. L. Andrew ◽  
Wing-fai Ng
Keyword(s):  
Boundary Layer ◽  
Incidence Angle ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Shear Stresses ◽  
State University ◽  
Mean Flow ◽  
Flow Measurements ◽  
The Mean ◽  
Supersonic Wake

The turbulent character of the supersonic wake of a linear cascade of fan airfoils has been studied using a two-component laser-doppler anemometer. The cascade was tested in the Virginia Polytechnic Institute and State University intermittent wind tunnel facility, where the Mach and Reynolds numbers were 2.36 and 4.8 × 106, respectively. In addition to mean flow measurements, Reynolds normal and shear stresses were measured as functions of cascade incidence angle and streamwise locations spanning the near-wake and the far-wake. The extremities of profiles of both the mean and turbulent wake properties´ were found to be strongly influenced by upstream shock-boundary -layer interactions, the strength of which varied with cascade incidence. In contrast, the peak levels of turbulence properties within the shear layer were found to be largely independent of incidence, and could be characterized in terms of the streamwise position only. The velocity defect turbulence level was found to be 23 percent, and the generally accepted value of the turbulence structural coefficient of 0.30 was found to be valid for this flow. The degree of similarity of the mean flow wake profiles was established, and those profiles demonstrating the most similarity were found to approach a state of equilibrium between the mean and turbulent properties. In general, this wake flow may be described as a classical free shear flow, upon which the influence of upstream shock-boundary-layer interactions has been superimposed.

Turbulence Characteristics in a Supersonic Cascade Wake Flow

1993 ◽  
Author(s):  
Philip L. Andrew ◽  
Wing-fai Ng
Keyword(s):  
Boundary Layer ◽  
Incidence Angle ◽  
Reynolds Numbers ◽  
Wake Flow ◽  
Shear Stresses ◽  
State University ◽  
Mean Flow ◽  
Flow Measurements ◽  
The Mean ◽  
Supersonic Wake

The turbulent character of the supersonic wake of a linear cascade of fan airfoils has been studied using a two–component Laser Doppler Anemometer. The cascade was tested in the Virginia Polytechnic Institute and State University intermittent wind tunnel facility, where the Mach and Reynolds numbers were 2.36 and 4.8 × 106, respectively. In addition to mean flow measurements, Reynolds normal and shear stresses were measured as functions of cascade incidence angle and streamwise locations spanning the near–wake and the far–wake. The extremities of profiles of both the mean and turbulent wake properties were found to be strongly influenced by upstream shock–boundary–layer–interactions, the strength of which varied with cascade incidence. In contrast, the peak levels of turbulence properties within the shear layer were found to be largely independent of incidence, and could be characterized in terms of the streamwise position only. The velocity defect turbulence level was found to be 23%, and the generally–accepted value of the turbulence structural coefficient of 0.30 was found to be valid for this flow. The degree of similarity of the mean flow wake profiles was established, and those profiles demonstrating the most similarity were found to approach a state of equilibrium between the mean and turbulent properties. In general, this wake flow may be described as a classical free shear flow, upon which the influence of upstream shock–boundary–layer–interactions has been superimposed.

Turbulence Intensity Distribution for Flow Along a Streamwise External Corner

2002 ◽  
Author(s):  
Khalid A. M. Moinuddin ◽  
Peter N. Joubert ◽  
Min S. Chong
Keyword(s):  
Secondary Flow ◽  
Turbulence Intensity ◽  
Leading Edge ◽  
Two Dimensional ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
General Behaviour ◽  
Flow Measurements ◽  
Square Duct ◽  
Normal Distance

This work continues the studies of Moinuddin et al. [1], where experiments were performed on a streamwise external corner. The streamwise development of turbulent boundary layer over an external corner (chine) is influenced by secondary flow which is driven three-dimensionally. The direct effect of this secondary flow is to increase the drag force. Here secondary flow, which is known as Prandtl’s second kind, is induced by inequality of Reynolds stresses around the corner. This flow is expected to exhibit symmetry about the corner bisector. Moinuddin et al. [2,3] have established the symmetry of this flow based upon mean flow measurements. Normal wire measurements for the streamwise turbulence intensity profiles u′2+, measured at about Reθ 5700 and 4.7 m from the model leading edge, are presented in this paper. Mean flow measurements show excellent agreement between Pitot tube and normal wire measurements. Comparisons are made for u′2+, profiles at equal spanwise distance, from the corner, on both surfaces. The profiles agree quite well having nominal deviation depending on spanwise and normal distance from the corner. Isointensity contours also depict symmetrical turbulence distribution. It is also revealed that far from the corner, turbulence profiles agree well with the standard two-dimensional turbulence profile. The measurements agrees with the general behaviour expected from this kind of flow as reported by Xu & Pollard [4] from their LES calculation of flow in an annular square duct.

Mean Flow Measurements in Aortofemoral Arterial Reconstructions

1975 ◽  
Vol 45 (1) ◽  
pp. 17-21
Author(s):  
J. M. Little ◽  
A. G. R. Sheil ◽  
J. Loewenthal ◽  
J. May ◽  
A. H. Goodman
Keyword(s):  
Mean Flow ◽  
Flow Measurements

scholarly journals CFD Analysis of Urban Canopy Flows Employing the V2F Model: Impact of Different Aspect Ratios and Relative Heights

2018 ◽  
Vol 2018 ◽  
pp. 1-16 ◽  
Author(s):  
Fabio Nardecchia ◽  
Annalisa Di Bernardino ◽  
Francesca Pagliaro ◽  
Paolo Monti ◽  
Giovanni Leuzzi ◽  
...  
Keyword(s):  
Flow Field ◽  
Water Channel ◽  
Flow Regimes ◽  
Two Dimensional ◽  
Mean Flow ◽  
Ansys Fluent ◽  
Practical Applications ◽  
Aspect Ratios ◽  
Starting Point ◽  
Step Down

Computational fluid dynamics (CFD) is currently used in the environmental field to simulate flow and dispersion of pollutants around buildings. However, the closure assumptions of the turbulence usually employed in CFD codes are not always physically based and adequate for all the flow regimes relating to practical applications. The starting point of this work is the performance assessment of the V2F (i.e., v2¯ − f) model implemented in Ansys Fluent for simulating the flow field in an idealized array of two-dimensional canyons. The V2F model has been used in the past to predict low-speed and wall-bounded flows, but it has never been used to simulate airflows in urban street canyons. The numerical results are validated against experimental data collected in the water channel and compared with other turbulence models incorporated in Ansys Fluent (i.e., variations of both k-ε and k-ω models and the Reynolds stress model). The results show that the V2F model provides the best prediction of the flow field for two flow regimes commonly found in urban canopies. The V2F model is also employed to quantify the air-exchange rate (ACH) for a series of two-dimensional building arrangements, such as step-up and step-down configurations, having different aspect ratios and relative heights of the buildings. The results show a clear dependence of the ACH on the latter two parameters and highlight the role played by the turbulence in the exchange of air mass, particularly important for the step-down configurations, when the ventilation associated with the mean flow is generally poor.

Measurements of Apparent Mass Torque Coefficients of Two-Dimensional Centrifugal Impellers

1986 ◽  
Vol 108 (4) ◽  
pp. 407-413
Author(s):  
Y. Tsujimoto ◽  
K. Imaichi ◽  
T. Moritani ◽  
K. Kim
Keyword(s):  
Angular Velocity ◽  
Flow Rate ◽  
Potential Flow ◽  
Rotational Velocity ◽  
Apparent Mass ◽  
Two Dimensional ◽  
Drag Torque ◽  
Mean Flow ◽  
Experimental Values

Apparent mass torque coefficients for fluctuations of flow rate and angular velocity are determined experimentally for two-dimensional centrifugal impellers. Nearly sinusoidal fluctuations of flow rate and angular velocity are produced by using crank mechanisms, and the resulting unsteady torque on the impeller is measured. The torque is divided into components in-phase and out-of-phase with the displacements. The in-phase components are used to determine the apparent mass coefficients. Drag torque coefficients are defined and used to represent the out-of-phase components. The tests are conducted under various frequencies and amplitudes of the fluctuations with zero mean flow rate and rotational velocity. The apparent mass torque coefficients are compared with theoretical values obtained under the assumption of a two-dimensional potential flow. The experimental values are 5 to 20 percent larger than the theoretical ones and no appreciable effects of the frequency and the amplitude are observed within the range of the experiments.

Investigation of the Flow Field in a HP Turbine Stage for Two Stator-Rotor Axial Gaps: Part II — Unsteady Flow Field

2006 ◽  
Author(s):  
P. Gaetani ◽  
G. Persico ◽  
V. Dossena ◽  
C. Osnaghi
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Dominant Role ◽  
Outer Part ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Turbine Stage ◽  
Mean Flow ◽  
Tip Leakage Flow ◽  
Flow Measurements

An extensive experimental analysis was carried out at Politecnico di Milano on the subject of unsteady flow in high pressure (HP) turbine stages. In this paper the unsteady flow measured downstream of a modern HP turbine stage is discussed. Traverses in two planes downstream of the rotor are considered and, in one of them, the effects of two very different axial gaps are investigated: the maximum axial gap, equal to one stator axial chord, is chosen to “switch off” the rotor inlet unsteadiness, while the nominal gap, equal to 1/3 of the stator axial chord, is representative of actual engines. The experiments were performed by means of a fast-response pressure probe, allowing for two-dimensional phase-resolved flow measurements in a bandwidth of 80 kHz. The main properties of the probe and the data processing are described. The core of the paper is the analysis of the unsteady rotor aerodynamics; for this purpose, instantaneous snapshots of the rotor flow in the relative frame are used. The rotor mean flow and its interaction with the stator wakes and vortices are also described. In the outer part of the channel only the rotor cascade effects can be observed, with a dominant role played by the tip-leakage flow and by the rotor tip passage vortex. In the hub region, where the secondary flows downstream of the stator are stronger, the persistence of stator vortices is slightly visible in the maximum stator-rotor axial gap configuration, while in the minimum stator-rotor axial gap configuration the interaction with the rotor vortices dominates the flow field. A fair agreement with the wakes and vortices transport models has been achieved. A discussion of the interaction process is reported giving particular emphasis to the effects of the different cascade axial gaps. Some final considerations on the effects of the different axial gap over the stage performances are reported.

scholarly journals Magnetoconvection in a horizontal duct flow at very high Hartmann and Grashof numbers

2021 ◽  
Vol 931 ◽  
Author(s):  
R. Akhmedagaev ◽  
O. Zikanov ◽  
Y. Listratov
Keyword(s):  
Magnetic Field ◽  
Magnetic Field Effect ◽  
Dimensional Structure ◽  
Two Dimensional ◽  
Duct Flow ◽  
Mean Flow ◽  
Horizontal Magnetic Field ◽  
Nuclear Fusion Reactor ◽  
Dimensional Approximation ◽  
Very High

Direct numerical simulations and linear stability analysis are carried out to study mixed convection in a horizontal duct with constant-rate heating applied at the bottom and an imposed transverse horizontal magnetic field. A two-dimensional approximation corresponding to the asymptotic limit of a very strong magnetic field effect is validated and applied, together with full three-dimensional analysis, to investigate the flow's behaviour in the previously unexplored range of control parameters corresponding to typical conditions of a liquid metal blanket of a nuclear fusion reactor (Hartmann numbers up to $10^4$ and Grashof numbers up to $10^{10}$ ). It is found that the instability to quasi-two-dimensional rolls parallel to the magnetic field discovered at smaller Hartmann and Grashof numbers in earlier studies also occurs in this parameter range. Transport of the rolls by the mean flow leads to magnetoconvective temperature fluctuations of exceptionally high amplitudes. It is also demonstrated that quasi-two-dimensional structure of flows at very high Hartmann numbers does not guarantee accuracy of the classical two-dimensional approximation. The accuracy deteriorates at the highest Grashof numbers considered in the study.

Control of Hemorrhage in Critical Femoral or Inguinal Penetrating Wounds—An Ultrasound Evaluation

2006 ◽  
Vol 21 (6) ◽  
pp. 379-382 ◽  
Author(s):  
Michael Blaivas ◽  
Stephen Shiver ◽  
Matthew Lyon ◽  
Srikar Adhikari
Keyword(s):  
Flow Velocity ◽  
Abdominal Aorta ◽  
Femoral Artery ◽  
Iliac Artery ◽  
Common Femoral Artery ◽  
Body Armor ◽  
Mean Flow ◽  
Mean Velocity ◽  
Flow Measurements ◽  
Ultrasound Evaluation

AbstractIntroduction:Exsanguination from a femoral artery wound can occur in sec-onds and may be encountered more often due to increased use of body armor. Some military physicians teach compression of the distal abdominal aorta (Abdominal Aorta) with a knee or a fist as a temporizing measure.Objective:The objective of this study was to evaluate if complete collapse of the Abdominal Aorta was feasible and with what weight it occurs.Methods:This was a prospective, interventional study at a Level-I, academ-ic, urban, emergency department with an annual census of 80,000 patients. Written, informed consent was obtained from nine male volunteers after Institutional Research Board approval. Any patient who presented with abdominal pain or had undergone previous abdominal surgery was excluded from the study. Subjects were placed supine on the floor to simulate an injured soldier. Various dumbbells of increasing weight were placed over the distal Abdominal Aorta, and pulsed-wave Doppler measurements were taken at the right common femoral artery (CFA). Dumbbells were placed on top of a tightly bundled towel roughly the surface area of an adult knee. Flow measurements at the CFA were taken at increments of 20 pounds. This was repeated with weight over the proximal right artery iliac and distal right iliac artery to eval- uate alternate sites. Descriptive statistics were utilized to evaluate the data.Results:The mean velocity through the CFA was 75.8 cm/ sec at 0 pounds. Compression of the Abdominal Aorta ranging 80 to 140 pounds resulted in no flow in the CFA. A steady decrease in mean flow velocity was seen starting with 20 pounds. Flow velocity decreased more rapidly with compression of the prox- imal right iliac artery, and stopped in all nine volunteers by 120 pounds of pressure. For all nine volunteers, up to 80 pounds of pressure over the distal iliac artery failed to decrease CFA flow velocity, and no subject was able to tolerate more weight at that location.Conclusion:Flow to the CFA can be stopped completely with pressure over the distal Abdominal Aorta or proximal iliac artery in catastrophic wounds. Compression over the proximal iliac artery worked best, but a first responder still may need to apply upward of 120 pounds of pressure to stop exsanguination.

Highly resolved experimental results of the separated flow in a channel with streamwise periodic constrictions

2016 ◽  
Vol 796 ◽  
pp. 257-284 ◽  
Author(s):  
Christian J. Kähler ◽  
Sven Scharnowski ◽  
Christian Cierpka
Keyword(s):  
Turbulent Flow ◽  
Flow Separation ◽  
Flow Direction ◽  
Separated Flow ◽  
Mean Flow ◽  
Complex Flow ◽  
Flow Measurements ◽  
Flow Features ◽  
Wall Flow ◽  
Near Wall

The understanding and accurate prediction of turbulent flow separation on smooth surfaces is still a challenging task because the separation and the reattachment locations are not fixed in space and time. Consequently, reliable experimental data are essential for the validation of numerical flow simulations and the characterization and analysis of the complex flow physics. However, the uncertainty of the existing near-wall flow measurements make a precise analysis of the near-wall flow features, such as separation/reattachment locations and other predicted near-wall flow features which are under debate, often impossible. Therefore, the periodic hill experiment at TU Munich (ERCOFTAC test case 81) was repeated using high resolution particle image velocimetry and particle tracking velocimetry. The results confirm the strong effect of the spatial resolution on the near-wall flow statistics. Furthermore, it is shown that statistically stable values of the turbulent flow variables can only be obtained for averaging times which are challenging to realize with highly resolved large eddy simulation and direct numerical simulation techniques. Additionally, the analysis implies that regions of correlated velocity fluctuations with rather uniform streamwise momentum exist in the flow. Their size in the mean flow direction can be larger than the hill spacing. The possible impact of the correlated turbulent motion on the wake region is discussed, as this interaction might be important for the understanding and control of the flow separation dynamics on smooth bodies.

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