A Quantitative Comparison of Delta Wing Vortices in the Near-Wake For Incompressible and Supersonic Free Streams

2005 ◽  
Vol 127 (6) ◽  
pp. 1071-1084 ◽  
Author(s):  
Frank Y. Wang ◽  
Ivana M. Milanovic ◽  
Khairul B. M. Q. Zaman ◽  
Louis A. Povinelli
Keyword(s):  
Incompressible Flow ◽  
Axial Velocity ◽  
High Speed ◽  
Delta Wing ◽  
Vortex Pair ◽  
Pressure Probe ◽  
Spanwise Direction ◽  
Near Wake ◽  
Low Speed ◽  
Axis Switching

When requiring quantitative data on delta wing vortices for design purposes, low-speed results have often been extrapolated to configurations intended for supersonic operation. This practice stems from a lack of database in high-speed flows due to measurement difficulties. In the present paper an attempt is made to examine this practice by comparing data from an incompressible flow experiment designed specifically to correspond to an earlier experiment in supersonic flows. The comparison is made for a 75° sweptback delta wing at angles of attack of 7° and 12°. For the incompressible flow, detailed flow-field properties including vorticity and turbulence characteristics are obtained by hot-wire and pressure probe surveys. The results are compared, wherever possible, with available data from the earlier Mach 2.49 experiment. The results indicate that quantitative similarities exist in the distributions of total pressure and swirl velocities. Qualitative similarities also exist in other properties, however, many differences are observed. The vortex core is smaller and rounded at low speed. At high speed, it is elongated in the spanwise direction near the trailing edge but goes through “axis switching” within a short distance downstream. The vortex is located farther outboard, i.e., the spacing between the two legs of the vortex pair is larger, at low speed. The axial velocity distribution within the core is significantly different in the two flow regimes. A “jet-like” profile, observed at low speed, either disappears or becomes “wake-like” at high speed. The axial velocity characteristics are examined in the light of an analytical model.

Flow Investigation Through a 30° Turn Diffusing Duct in Subsonic Flow Regime

2009 ◽  
Author(s):  
Prasanta K. Sinha ◽  
Biswajit Haldar ◽  
Amar N. Mullick ◽  
Bireswar Majumdar
Keyword(s):  
Axial Velocity ◽  
Pressure Loss ◽  
Total Pressure ◽  
High Speed ◽  
Static Pressure ◽  
Transverse Velocity ◽  
Total Pressure Loss ◽  
Pressure Recovery ◽  
Pressure Probe ◽  
Mean Velocity

Curved diffusers are an integral component of the gas turbine engines of high-speed aircraft. These facilitate effective operation of the combustor by reducing the total pressure loss. The performance characteristics of these diffusers depend on their geometry and the inlet conditions. In the present investigation the distribution of axial velocity, transverse velocity, mean velocity, static and total pressures are experimentally studied on a curved diffuser of 30° angle of turn with an area ratio of 1.27. The centreline length was chosen as three times of inlet diameter. The experimental results then were numerically validated with the help of Fluent, the commercial CFD software. The measurements of axial velocity, transverse velocity, mean velocity, static pressure and total pressure distribution were taken at Reynolds number 1.9 × 105 based on inlet diameter and mass average inlet velocity. The mean velocity and all the three components of mean velocity were measured with the help of a pre-calibrated five-hole pressure probe. The velocity distribution shows that the flow is symmetrical and uniform at the inlet and exit sections and high velocity cores are accumulated at the top concave surface due to the combined effect of velocity diffusion and centrifugal action. It also indicates the possible development of secondary motions between the concave and convex walls of the test diffuser. The mass average static pressure recovery and total pressure loss within the curved diffuser increases continuously from inlet to exit and they attained maximum values of 35% and 14% respectively. A comparison between the experimental and predicated results shows a good qualitative agreement between the two. Standard k-ε model in Fluent solver was chosen for validation. It has been observed that coefficient of pressure recovery Cpr for the computational investigation was obtained as 38% compared to the experimental investigation which was 35% and the coefficient of pressure loss is obtained as 13% in computation investigation compared to the 14% in experimental study, which indicates a very good qualitative matching.

Streamwise vortices associated with the bursting phenomenon

1979 ◽  
Vol 94 (3) ◽  
pp. 577-594 ◽  
Author(s):  
Ron F. Blackwelder ◽  
Helmut Eckelmann
Keyword(s):  
High Speed ◽  
Vortex Pair ◽  
Turbulent Shear ◽  
Sampling Techniques ◽  
Wall Region ◽  
Turbulent Shear Flow ◽  
Streamwise Vortices ◽  
Defect Region ◽  
Low Speed ◽  
Hot Film

The streamwise and spanwise velocity components and the gradients of these components normal to the wall were examined by using hot-film sensors and flush-mounted wall elements to study the vortex structures associated with the bursting phenomenon. Quadrant probability analysis and conditional sampling techniques indicated that pairs of counter-rotating streamwise vortices occur frequently in the wall region of a bounded turbulent shear flow. A streamwise momentum defect occurred between the vortices as low-speed fluid was ‘pumped’ away from the wall by the vortex pair. The defect region was long and narrow and possibly forms the low-speed streak as observed in visualization studies. The velocity defect was terminated by a strong acceleration followed by a high speed region.

High Speed Testing and Numerical Validation of an Aggressive Intermediate Compressor Duct

2013 ◽  
Author(s):  
Fredrik Wallin ◽  
Jörgen Olsson ◽  
Peter P. J. Johansson ◽  
Euodia Krüger ◽  
Martin Olausson
Keyword(s):  
Surface Roughness ◽  
High Speed ◽  
Test Facility ◽  
Pressure Probe ◽  
Low Speed ◽  
Geometrical Properties ◽  
Speed Test ◽  
Surface Finishes ◽  
Roughness Model ◽  
The Uk

An experimental and numerical investigation of the flow in an s-shaped compressor duct is presented in this paper. The experimental test was conducted in the compressor test facility at STARCS in Bromma, Sweden. The duct was designed based on geometrical properties of corresponding low-speed tests performed at the Universities of Cambridge and Loughborough in the UK in the EU research project AIDA. For the high-speed test, the geometry was scaled to fit the downstream compressor, keeping the non-dimensional characteristics of the duct as similar to the low-speed configurations as possible. Extensive CFD calculations were performed to assist the set-up of the test and to predict the duct performance in detail. The duct was equipped with static pressure taps on hub and shroud as well as on the strut. The duct inlet and exit flowfields were scanned using a miniature five-hole pressure probe that provided total pressure, velocities and flow angles. Two different duct surface finishes were tested at two different compressor operational points. Using the five-hole probe results, the duct loss could be estimated and compared to that of the CFD. For the CFD analysis a surface roughness model was used to account for the different surface finishes of the duct. The results show that using the surface roughness model makes it possible to account for the increase in loss due to a rougher flow surface. The absolute loss values are however under-predicted by approximately 10% in the CFD compared to the experiments.

Do You Name Speedy Objects Faster Than Slow Objects: SPEEDED NAMING OR NAMING SPEED? THE AUTOMATIC EFFECT OF OBJECT SPEED ON PERFORMANCE

2018 ◽  
Author(s):  
Moshe Shay Ben-Haim ◽  
Eran Chajut ◽  
Ran Hassin ◽  
Daniel Algom
Keyword(s):  
High Speed ◽  
Mental Representations ◽  
Reading Aloud ◽  
Naming Task ◽  
Naming Speed ◽  
Low Speed ◽  
Everyday Objects ◽  
Pictures And Words

we test the hypothesis that naming an object depicted in a picture, and reading aloud an object’s name, are affected by the object’s speed. We contend that the mental representations of everyday objects and situations include their speed, and that the latter influences behavior in instantaneous and systematic ways. An important corollary is that high-speed objects are named faster than low-speed objects despite the fact that object speed is irrelevant to the naming task at hand. The results of a series of 7 studies with pictures and words support these predictions.

scholarly journals Splatters and Aerosols Contamination in Dental Aerosol Generating Procedures

2021 ◽  
Vol 11 (4) ◽  
pp. 1914
Author(s):  
Pingping Han ◽  
Honghui Li ◽  
Laurence J. Walsh ◽  
Sašo Ivanovski
Keyword(s):  
Particle Size ◽  
Disease Transmission ◽  
High Speed ◽  
Low Speed ◽  
Dental Procedures ◽  
Dental Equipment ◽  
Produce Contamination ◽  
Fluorescein Dye ◽  
Filter Papers ◽  
Airborne Disease

Dental aerosol-generating procedures produce a large amount of splatters and aerosols that create a major concern for airborne disease transmission, such as COVID-19. This study established a method to visualise splatter and aerosol contamination by common dental instrumentation, namely ultrasonic scaling, air-water spray, high-speed and low-speed handpieces. Mock dental procedures were performed on a mannequin model, containing teeth in a typodont and a phantom head, using irrigation water containing fluorescein dye as a tracer. Filter papers were placed in 10 different locations to collect splatters and aerosols, at distances ranging from 20 to 120 cm from the source. All four types of dental equipment produced contamination from splatters and aerosols. At 120 cm away from the source, the high-speed handpiece generated the greatest amount and size (656 ± 551 μm) of splatter particles, while the triplex syringe generated the largest amount of aerosols (particle size: 1.73 ± 2.23 μm). Of note, the low-speed handpiece produced the least amount and size (260 ± 142 μm) of splatter particles and the least amount of aerosols (particle size: 4.47 ± 5.92 μm) at 120 cm. All four dental AGPs produce contamination from droplets and aerosols, with different patterns of distribution. This simple model provides a method to test various preventive strategies to reduce risks from splatter and aerosols.

Nonlinear transport of rarefied Couette flows from low speed to high speed

2020 ◽  
Vol 32 (11) ◽  
pp. 112021
Author(s):  
Jihui Ou ◽  
Jie Chen
Keyword(s):  
High Speed ◽  
Nonlinear Transport ◽  
Low Speed

scholarly journals Energy Absorption Characteristics of PVC Coarse Aggregate Concrete under Impact Load

2021 ◽  
Vol 15 (1) ◽  
Author(s):  
Shi Hu ◽  
Huaming Tang ◽  
Shenyao Han
Keyword(s):  
Compressive Strength ◽  
Energy Absorption ◽  
High Speed ◽  
Coarse Aggregate ◽  
Specific Energy Absorption ◽  
Low Speed ◽  
High Speed Impact ◽  
Aggregate Content ◽  
Dynamic Compressive Strength ◽  
Absorption Characteristics

AbstractIn this paper, polyvinyl chloride (PVC) coarse aggregate with different mixing contents is used to solve the problems of plastic pollution, low energy absorption capacity and poor damage integrity, which provides an important reference for PVC plastic concrete used in the initial support structures of highway tunnels and coal mine roadway. At the same time, the energy absorption characteristics and their relationship under different impact loads are studied, which provides an important reference for predicting the energy absorption characteristics of concrete under other PVC aggregate content or higher impact speed. This study replaced natural coarse aggregate in concrete with different contents and equal volume of well-graded flaky PVC particles obtained by crushing PVC soft board. Also, slump, compression, and splitting strength tests, a free falling low-speed impact test of steel balls and a high-speed impact compression test of split Hopkinson pressure bar (SHPB) were carried out. Results demonstrate that the static and dynamic compressive strength decreases substantially, and the elastic modulus and slump decrease slowly with the increase of the mixing amount of PVC aggregate (0–30%). However, the energy absorption rate under low-speed impact and the specific energy absorption per MPa under high-speed impact increase obviously, indicating that the energy absorption capacity is significantly enhanced. Regardless of the mixing amount of PVC aggregate, greater strain rate can significantly enhance the dynamic compressive strength and the specific energy absorption per MPa. After the uniaxial compression test or the SHPB impact test, the relative integrity of the specimen is positively correlated with the mixing amount of PVC aggregate. In addition, the specimens are seriously damaged with the increase of the impact strain rate. When the PVC aggregate content is 20%, the compressive strength and splitting strength of concrete are 33.8 MPa and 3.26 MPa, respectively, the slump is 165 mm, the energy absorption rate under low-speed impact is 89.5%, the dynamic compressive strength under 0.65 Mpa impact air pressure is 58.77 mpa, and the specific energy absorption value per MPa is 13.33, which meets the requirements of shotcrete used in tunnel, roadway support and other impact loads. There is a linear relationship between the energy absorption characteristics under low-speed impact and high-speed impact. The greater the impact pressure, the larger the slope of the fitting straight line. The slope and intercept of the fitting line also show a good linear relationship with the increase of impact pressure. The conclusions can be used to predict the energy absorption characteristics under different PVC aggregate content or higher-speed impact pressure, which can provide important reference for safer, more economical, and environmental protection engineering structure design.

Steady longitudinal vortices in supersonic turbulent separated flows

2011 ◽  
Vol 672 ◽  
pp. 451-476 ◽  
Author(s):  
ERICH SCHÜLEIN ◽  
VICTOR M. TROFIMOV
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Roughness Element ◽  
Vortex Generator ◽  
Vortex Pair ◽  
Leading Edge ◽  
Separated Flows ◽  
Vortex Generators ◽  
Longitudinal Vortices ◽  
Oil Flow

Large-scale longitudinal vortices in high-speed turbulent separated flows caused by relatively small irregularities at the model leading edges or at the model surfaces are investigated in this paper. Oil-flow visualization and infrared thermography techniques were applied in the wind tunnel tests at Mach numbers 3 and 5 to investigate the nominally 2-D ramp flow at deflection angles of 20°, 25° and 30°. The surface contour anomalies have been artificially simulated by very thin strips (vortex generators) of different shapes and thicknesses attached to the model surface. It is shown that the introduced streamwise vortical disturbances survive over very large downstream distances of the order of 104 vortex-generator heights in turbulent supersonic flows without pressure gradients. It is demonstrated that each vortex pair induced in the reattachment region of the ramp is definitely a child of a vortex pair, which was generated originally, for instance, by the small roughness element near the leading edge. The dependence of the spacing and intensity of the observed longitudinal vortices on the introduced disturbances (thickness and spanwise size of vortex generators) and on the flow parameters (Reynolds numbers, boundary-layer thickness, compression corner angles, etc.) has been shown experimentally.

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