Straight-Walled, Two-Dimensional Diffusers—Transitory Stall and Peak Pressure Recovery

1980 ◽  
Vol 102 (3) ◽  
pp. 275-282 ◽  
Author(s):  
J. Ashjaee ◽  
J. P. Johnston
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Mach Number ◽  
Aspect Ratio ◽  
Peak Pressure ◽  
Flow Direction ◽  
Prediction Method ◽  
Pressure Recovery ◽  
Two Dimensional ◽  
Large Aspect Ratio

Straight-walled, two-dimensional diffusers of large aspect ratio were investigated experimentally for the purpose of studying the regime of incipient transitory stall, the location of the geometry of peak diffuser pressure recovery. Twelve symmetric diffusers of constant nondimensional length (L/W1 = 15) with total included angles ranging from 4 to 24 degrees, covering attached, intermittently detaching, and unsteady detached flows were examined. Tests were run at one inlet blockage, 2δ1 / W1 = 0.027, and at an inlet Reynolds number of U1 W1/ν = 2.2 × 105 with air flow at low inlet Mach number. Pressure recovery and flow direction intermittency were obtained along the diffuser walls. An objective comparison of the UIM method of Ghose and Kline and an improved prediction method [Appendix] was performed with respect to these new experimental data. Some new conclusions are drawn concerning the nature of the flow in the vicinity of peak pressure recovery.

Effect of Compressibility on Gaseous Flows in a Micro-Tube

2003 ◽  
Author(s):  
Yutaka Asako ◽  
Kenji Nakayama
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Pressure Distribution ◽  
Flow Characteristics ◽  
Fused Silica ◽  
Two Dimensional ◽  
Arbitrary Lagrangian Eulerian ◽  
Gaseous Flow ◽  
Gaseous Flows ◽  
Energy Equations

The product of friction factor and Reynolds number (f·Re) of gaseous flow in the quasi-fully developed region of a micro-tube was obtained experimentally and numerically. The tube cutting method was adopted to obtain the pressure distribution along the tube. The fused silica tubes whose nominal diameters were 100 and 150 μm, were used. Two-dimensional compressible momentum and energy equations were solved to obtain the flow characteristics in micro-tubes. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The both results agree well and it was found that (f·Re) is a function of Mach number.

scholarly journals Linear biglobal analysis of Rayleigh–Bénard instabilities in binary fluids with and without throughflow

2012 ◽  
Vol 713 ◽  
pp. 216-242 ◽  
Author(s):  
Jun Hu ◽  
Daniel Henry ◽  
Xie-Yuan Yin ◽  
Hamda BenHadid
Keyword(s):  
Reynolds Number ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Critical Rayleigh Number ◽  
Two Dimensional ◽  
Binary Fluids ◽  
Transverse Modes ◽  
Aspect Ratios ◽  
Rayleigh Benard ◽  
Mode A

AbstractThree-dimensional Rayleigh–Bénard instabilities in binary fluids with Soret effect are studied by linear biglobal stability analysis. The fluid is confined transversally in a duct and a longitudinal throughflow may exist or not. A negative separation factor $\psi = \ensuremath{-} 0. 01$, giving rise to oscillatory transitions, has been considered. The numerical dispersion relation associated with this stability problem is obtained with a two-dimensional Chebyshev collocation method. Symmetry considerations are used in the analysis of the results, which allow the classification of the perturbation modes as ${S}_{l} $ modes (those which keep the left–right symmetry) or ${R}_{x} $ modes (those which keep the symmetry of rotation of $\lrm{\pi} $ about the longitudinal mid-axis). Without throughflow, four dominant pairs of travelling transverse modes with finite wavenumbers $k$ have been found. Each pair corresponds to two symmetry degenerate left and right travelling modes which have the same critical Rayleigh number ${\mathit{Ra}}_{c} $. With the increase of the duct aspect ratio $A$, the critical Rayleigh numbers for these four pairs of modes decrease and closely approach the critical value ${\mathit{Ra}}_{c} = 1743. 894$ obtained in a two-dimensional situation, one of the mode (a ${S}_{l} $ mode called mode A) always remaining the dominant mode. Oscillatory longitudinal instabilities ($k\approx 0$) corresponding to either ${S}_{l} $ or ${R}_{x} $ modes have also been found. Their critical curves, globally decreasing, present oscillatory variations when the duct aspect ratio $A$ is increased, associated with an increasing number of longitudinal rolls. When a throughflow is applied, the symmetry degeneracy of the pairs of travelling transverse modes is broken, giving distinct upstream and downstream modes. For small and moderate aspect ratios $A$, the overall critical Rayleigh number in the small Reynolds number range studied is only determined by the upstream transverse mode A. In contrast, for larger aspect ratios as $A= 7$, different modes are successively dominant as the Reynolds number is increased, involving both upstream and downstream transverse modes A and even the longitudinal mode.

Heat Transfer in a Rotating Two-Pass Rectangular Channel Featuring Reduced Cross-Sectional Area After Tip Turn (Aspect Ratio = 4:1 to 2:1) With Profiled 60 deg Angled Ribs

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Andrew F Chen ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han ◽  
Robert Krewinkel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Direction ◽  
Rectangular Channel ◽  
Secondary Flows ◽  
Transfer Coefficients ◽  
First Passage ◽  
Cross Sectional ◽  
Internal Surfaces

The present study features a two-pass rectangular channel with an aspect ratio (AR) = 4:1 in the first pass and an AR = 2:1 in the second pass after a 180-deg tip turn. In addition to the smooth-wall case, ribs with a profiled cross section are placed at 60 deg to the flow direction on both the leading and trailing surfaces in both passages (P/e = 10, e/Dh ∼ 0.11, parallel and in-line). Regionally averaged heat transfer measurement method was used to obtain the heat transfer coefficients on all internal surfaces. The Reynolds number (Re) ranges from 10,000 to 70,000 in the first passage, and the rotational speed ranges from 0 to 400 rpm. Under pressurized condition (570 kPa), the highest rotation number achieved was Ro = 0.39 in the first passage and 0.16 in the second passage. The results showed that the turn-induced secondary flows are reduced in an accelerating flow. The effects of rotation on heat transfer are generally weakened in the ribbed case than the smooth case. Significant heat transfer reduction (∼30%) on the tip wall was seen in both the smooth and ribbed cases under rotating condition. Overall pressure penalty was reduced for the ribbed case under rotation. Reynolds number effect was found noticeable in the current study. The heat transfer and pressure drop characteristics are sensitive to the geometrical design of the channel and should be taken into account in the design process.

Visualization and Analysis of Flow in an Offset Channel

1992 ◽  
Vol 114 (4) ◽  
pp. 819-826 ◽  
Author(s):  
J. A. Walter ◽  
C.-J. Chen
Keyword(s):  
Reynolds Number ◽  
Velocity Field ◽  
Nuclear Power ◽  
Flow Direction ◽  
Symmetry Plane ◽  
Two Dimensional ◽  
Plant Design ◽  
Duct Flow ◽  
Inlet Channel ◽  
Cross Sectional

This paper investigates flow characteristics for a benchmark experiment that is important for thermal hydraulic phenomena in nuclear power plant design. The flow visualization experiment is carried out for flow in a rectangular offset channel covering both the laminar and turbulent flow regimes. The Reynolds number, based on the inlet velocity and the height of the inlet channel, ranges from 25 to 4600. The offset channel is an idealized thermal hydraulic geometry. Duct flow expands in a rectangular chamber and exits to a duct that is offset from the entrance duct. The offset geometry creates zones of recirculation for thermal-hydraulic mixing. Flow patterns are visualized by a laser light sheet in the symmetry plane of the primary flow direction and in three cross-sectional planes. A charge-coupled device (CCD) images the flow field, simplifying the experimental process and subsequent image analyses. The flow pattern and size of the recirculation zones change dramatically with Reynolds number until the flow is fully turbulent. While the velocity field itself is predominantly two dimensional, it is shown that the walls of the chamber produce a fully three-dimensional flow that could not be predicted properly by a two-dimensional calculation. Quantitative measurements of particle pathlines from several images are superimposed to give a composite view of the velocity field at one of the Reynolds numbers examined.

Viscous Faraday waves in two-dimensional large-aspect-ratio containers

2006 ◽  
Vol 560 ◽  
pp. 369 ◽  
Author(s):  
FRANCISCO J. MANCEBO ◽  
JOSÉ M. VEGA
Keyword(s):  
Aspect Ratio ◽  
Two Dimensional ◽  
Large Aspect Ratio ◽  
Faraday Waves

Three-Dimensional Simulation of Gas Flow in Microducts

2005 ◽  
Author(s):  
Abhishek Agrawal ◽  
Amit Agrawal
Keyword(s):  
Aspect Ratio ◽  
Knudsen Number ◽  
Gas Flow ◽  
Flow Direction ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Theoretical Development ◽  
Width Ratio ◽  
Two Dimensional

Three-dimensional lattice Boltzmann method based simulations of a microduct have been undertaken in this paper. The objective is to understand the different physical phenomena occurring at these small scales and to investigate when the flow can be treated as two-dimensional. Towards this end, the Knudsen number and aspect ratio (depth to width ratio) are varied for a fixed pressure ratio. The pressure in the microduct is non-linear with the non-linearity in pressure reducing with an increase in Knudsen number. The pressure and velocity behaves somewhat similar to two-dimensional microchannels even when the aspect ratio is unity. The slip velocity at the impenetrable wall has two components: along and perpendicular to the flow. Our results show that the streamwise velocity near the centerline is relatively invariant along the depth for aspect ratio more than three, suggesting that the microduct can be modeled as a two-dimensional microchannel. However, the velocity component along the depth is never identically zero, implying that the flow is not truly two-dimensional. A curious change in vector direction in a plane normal to the flow direction is observed around aspect ratio of four. These first set of three-dimensional results are significant because they will help in theoretical development and flow modeling at micro scales.

Straight Channel Diffuser Performance at High Inlet Mach Numbers

1969 ◽  
Vol 91 (3) ◽  
pp. 397-412 ◽  
Author(s):  
P. W. Runstadler ◽  
R. C. Dean
Keyword(s):  
Mach Number ◽  
Aspect Ratio ◽  
Pressure Recovery ◽  
Straight Channel ◽  
Single Plane ◽  
Aspect Ratios ◽  
Straight Wall ◽  
Throat Width ◽  
Mach Numbers

Measurements have been made of the pressure recovery of straight wall, single plane divergence diffusers with inlet Mach numbers between 0.2 and choking (0.2 ≤ Mt < 1.0). In contrast to the widely held assertion in the literature, there is no “critical” inlet subsonic Mach number above which pressure recovery decreases drastically. Two aspect ratios, AS = 0.25 and 1.0, have been studied for a range of length-to-throat-width ratios L/W1 and divergence angles 2θ around the regions of peak recovery. Diffuser performance maps are given showing pressure recovery Cp as a function of diffuser geometry for fixed values of throat Mach number Mt, throat blockage B, and aspect ratio AS. Significant changes in the location and magnitude of pressure recovery do occur with variations in Mt, B, and AS. The importance to the designer of a knowledge of how diffuser performance depends upon geometric and diffuser inlet parameters is discussed.

Low Reynolds numbers flow past an ellipsoid of revolution of large aspect ratio

1965 ◽  
Vol 23 (4) ◽  
pp. 657-671 ◽  
Author(s):  
Yun-Yuan Shi
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Three Dimensional ◽  
Major Axis ◽  
Reynolds Numbers ◽  
The Body ◽  
Large Aspect Ratio ◽  
Low Reynolds Numbers ◽  
Ellipsoid Of Revolution ◽  
Limiting Case

The results of Proudman & Pearson (1957) and Kaplun & Lagerstrom (1957) for a sphere and a cylinder are generalized to study an ellipsoid of revolution of large aspect ratio with its axis of revolution perpendicular to the uniform flow at infinity. The limiting case, where the Reynolds number based on the minor axis of the ellipsoid is small while the other Reynolds number based on the major axis is fixed, is studied. The following points are deduced: (1) although the body is three-dimensional the expansion is in inverse power of the logarithm of the Reynolds number as the case of a two-dimensional circular cylinder; (2) the existence of the ends and the variation of the diameter along the axis of revolution have no effect on the drag to the first order; (3) a formula for drag is obtained to higher order.

Resistance of Two Inclined Parallel Flat Plates Placed in Tandem on a Stream-Wise Flat Plate in Two-Dimensional Flow

1993 ◽  
Vol 207 (6) ◽  
pp. 393-397
Author(s):  
R C Mehta ◽  
C R Rao ◽  
Y N Dubey
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Flat Plate ◽  
Flow Direction ◽  
Considerable Extent ◽  
Appreciable Effect ◽  
Two Dimensional ◽  
Flat Plates ◽  
Dimensional Flow ◽  
Two Dimensional Flow

The paper presents the results of an experimental study on the drag coefficient of two inclined parallel flat plates, placed on a stream-wise flat plate, in tandem, in two-dimensional flow. The effects on the drag coefficient of Reynolds number, the inclination of the plates to the flow direction and the relative spacing between plates were studied. It is observed that, while the Reynolds number has no appreciable effect, the other parameters influence the drag coefficient to a considerable extent. The results are corrected for blockage effect and comparisons are made with the data collected by other investigators.

Parametric Analysis of Turbulent Wall Jet in Still Air Over a Transitional Rough, With Asymptotes of Fully Rough and Fully Smooth Wall Jets

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Noor Afzal ◽  
Abu Seena
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Rough Surfaces ◽  
Flow Direction ◽  
Wall Jet ◽  
Functional Forms ◽  
Jet Velocity ◽  
Turbulent Wall ◽  
Momentum Integral ◽  
Power Law Index

The novel scalings for streamwise variations of the flow in a turbulent wall jet over a fully smooth, transitional, and fully rough surfaces have been analyzed. The universal scaling for arbitrary wall roughness is considered in terms of the roughness friction Reynolds number (that arises from the stream wise variations of roughness in the flow direction) and roughness Reynolds number at the nozzle jet exit. The transitional rough wall jet functional forms have been proposed, whose numerical constants power law index and prefactor are estimated from best fit to the data for several variables, like, maximum wall jet velocity, boundary layer thickness at maxima of wall jet velocity, the jet half width, the friction factor and momentum integral, which are supported by the experimental data. The data shows that the two asymptotes of fully rough and fully smooth surfaces are co-linear with transitional rough surface, predicting same constants for any variable of flow for full smooth, fully rough and transitional rough surfaces. There is no universality of scalings in terms of traditional variables as different expressions are needed for each stage of the transitional roughness. The experimental data provides very good support to our universal relations.

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