Effects of Bio-Inspired Micro-Scale Surface Patterns on the Profile Losses in a Linear Cascade

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Qiang Liu ◽  
Shan Zhong ◽  
Lin Li
Keyword(s):  
Pressure Loss ◽  
Reynolds Numbers ◽  
Loss Reduction ◽  
Turning Angle ◽  
Low Reynolds Numbers ◽  
Linear Cascade ◽  
Micro Scale ◽  
Pressure Loss Coefficient ◽  
Surface Patterns ◽  
Scale Surface

Abstract In this paper, we investigated the effects of herringbone riblets, a type of bio-inspired micro-scale surface patterns, on pressure losses and flow turning angles in a linear cascade over a range of low Reynolds numbers from 0.50 × 105 to 1.50 × 105 and at three different incidence angles. Our experiments showed that despite their micro-scale size, herringbone riblets produced a significant reduction in pressure loss and a substantial increase in flow turning angle except at the low end of the Reynolds numbers tested. In comparison to the baseline case without riblets, the highest reduction in the zone-averaged pressure loss coefficient behind one flow passage was 36.4% which was accompanied by a 4.1 deg increase in the averaged turning angle. The loss reduction was caused by a decrease in γmax at α = −1 deg, a narrower wake zone at α = 9 deg and a mixture of both at α = 4 deg due to the suppression of flow separation on the blade suction surface. It was also noted that such a significant improvement was always accompanied by the appearance of a serrated wake structure in the contours of pressure loss coefficient in which the region with a higher loss reduction occurring directly behind the divergent region of herringbone riblets. The observed improvement in cascade performance was attributed to the secondary flow motion produced by herringbone riblets which energizes the boundary layer. Overall, this work has produced convincing experimental evidence that herringbone riblets could be potentially used as passive flow control devices for reducing flow separation in compressors at low Reynolds numbers.

Implicit-LES Simulation of Variable-Speed Power Turbine Cascade for Low Free-Stream Turbulence Conditions

2018 ◽  
Author(s):  
Ali Ameri
Keyword(s):  
Free Stream ◽  
Reynolds Numbers ◽  
Scale Model ◽  
Variable Speed ◽  
Low Reynolds Numbers ◽  
Free Stream Turbulence ◽  
Pressure Loss Coefficient ◽  
Power Turbine ◽  
Actual Design ◽  
Low Reynolds

It is a challenge to simulate the flow in a Variable Speed Power Turbine (VSPT), or, for that matter, rear stages of low pressure turbines at low Reynolds numbers due to laminar flow separation or laminar/turbulent flow transition on the blades. At low Reynolds numbers, separation induced-transition is more prevalent which can result in efficiency lapse. LES has been used in recent years to simulate these types of flows with a good degree of success. In the present work, very low free stream turbulence flows at exit Reynolds number of 220k were simulated. The geometry was a cascade which was constructed with the midspan section of a VSPT design. Most LES simulations to date, have focused on the midspan region. As the endwall effect was significant in these simulations due to thick incoming boundary layer, full blade span computation was necessitated. Inlet flow angles representative of take-off and cruise conditions, dictated by the rotor speed in an actual design, were analyzed. This was done using a second order finite volume code and a high resolution grid. As is the case with Implicit-LES methods, no sub-grid scale model was used. Blade static pressure data, at various span locations, and downstream probe survey measurements of total pressure loss coefficient were used to verify the results. The comparisons showed good agreement between the simulations and the experimental data.

Pressure Losses and Limiting Reynolds Numbers for Non-Newtonian Fluids in Short Square-Edged Orifice Plates

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Butteur Ntamba Ntamba ◽  
Veruscha Fester
Keyword(s):  
Pressure Loss ◽  
Reynolds Numbers ◽  
Newtonian Fluids ◽  
Pressure Losses ◽  
Pressure Loss Coefficient ◽  
Stable Operating ◽  
Piping Systems ◽  
Laminar And Turbulent Flow ◽  
Loss Coefficients ◽  
Industrial Problem

Correlations predicting the pressure loss coefficient along with the laminar, transitional, and turbulent limiting Reynolds numbers with the β ratio are presented for short square-edged orifice plates. The knowledge of pressure losses across orifices is a very important industrial problem while predicting pressure losses in piping systems. Similarly, it is important to define stable operating regions for the application of a short orifice at lower Reynolds numbers. This work experimentally determined pressure loss coefficients for square-edged orifices for orifice-to-diameter ratios of β = 0.2, 0.3, 0.57, and 0.7 for Newtonian and non-Newtonian fluids in both laminar and turbulent flow regimes.

A Planar Micromixer Based on Sequential Logarithmic Spirals

2012 ◽  
Author(s):  
Thomas F. Scherr ◽  
Christian Quitadamo ◽  
Preston Tesvich ◽  
Daniel Sang-Won Park ◽  
Terrence Tiersch ◽  
...  
Keyword(s):  
Time Scale ◽  
Reynolds Numbers ◽  
Diffusive Transport ◽  
Low Reynolds Numbers ◽  
Micro Scale ◽  
Natural Time ◽  
Logarithmic Spirals ◽  
Microchannel Flows ◽  
Low Reynolds ◽  
Made In

Despite the advances made in recent years, mixing on the micro-scale remains a challenge. In typical microchannel flows, the lack of turbulence, evidenced by very low Reynolds numbers, constrains mixing to the natural time scale of diffusion. Peclet numbers, defined as the ratio of convective to diffusive transport, are typically very large in microfluidic applications, where transport is dominated by convection. As a result, a dedicated micromixing element is an integral part of most BioMEMS devices [1].

scholarly journals Investigation of Riblet Geometry and Start Locations of Herringbone Riblets on Pressure Losses in a Linear Cascade at Low Reynolds Numbers

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Qiang Liu ◽  
Shan Zhong ◽  
Lin Li
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Effective Control ◽  
Slight Reduction ◽  
Turning Angle ◽  
Low Reynolds Numbers ◽  
Pressure Losses ◽  
Lower Reynolds Number ◽  
Displacement Thickness ◽  
Low Reynolds

Abstract In this paper, the effects of an array of herringbone riblets with different riblet geometry (height and spacing) and start locations on the pressure losses in a cascade of diffuser blades are investigated over a range of low Reynolds numbers (0.50 × 105–1.00 × 105). The herringbone riblets with a given geometry are found to produce a profound modification to the wake structure above certain critical Reynolds numbers. It is also found that within the range of parameters tested an increase in riblet height and riblet spacing results in an onset of significant control effect at a lower Reynolds number, which is accompanied by a slight reduction in zone-averaged loss coefficient and flow turning angle. An upstream shift of the start position of the riblet array along the blades enables the riblets to become effective at a lower Reynolds number at the expense of a reduced loss reduction and flow turning angle. A semi-empirical relationship between the ratio of riblet height to local baseline boundary layer displacement thickness and the critical Reynolds number is established using the present experimental data. A preliminary methodology for designing the herringbone riblets to ensure an effective control of 2D flow separations around the mid-span of diffuser blades over a specified range of Reynolds numbers is also proposed.

Development of an Experimental Correlation for a Pressure Loss at a Side Orifice

2004 ◽  
Vol 127 (2) ◽  
pp. 388-392 ◽  
Author(s):  
Ho-Yun Nam ◽  
Jong-Man Kim ◽  
Kyung-Won Seo ◽  
Seok-Ki Choi
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Pressure Loss ◽  
Reynolds Numbers ◽  
Measured Data ◽  
Pressure Loss Coefficient ◽  
Liquid Metal Reactor ◽  
Experimental Correlation ◽  
Different Types ◽  
Reactor Fuel Assembly

An experimental study has been carried out to measure the pressure loss at the side orifice of a liquid metal reactor fuel assembly. The characteristics of the pressure loss at the side orifice are investigated using the experimental data measured from 17 different types of side orifices that have different geometric shapes, dimensions, and arrangements of nozzles, and a correlation that covers the whole flow range by one equation is developed. The error range of the correlation is within ±10%, and most of the errors occurred in a region where the Reynolds number is small. The range of Reynolds numbers based on the hydraulic diameter of the orifice is 2000–350,000. It is found that the geometric factor is the most important parameter for the pressure loss when the Reynolds number is >30,000. As the Reynolds number becomes smaller, its effect becomes larger, and when the Reynolds number is small, it is the most important parameter for the pressure loss at the side orifices. The measured data shows a trend that the pressure loss coefficient increases as the number of orifices increases, and the effect of the longitudinal arrangement is small.

Investigation on Drag Reduction Through Dimple Machining

2018 ◽  
Author(s):  
Majid TabkhPaz ◽  
Lindsay Howell ◽  
Zachary Kockerbeck ◽  
Simon Park ◽  
Ron Hugo
Keyword(s):  
Drag Reduction ◽  
Silicone Oil ◽  
Reynolds Numbers ◽  
System Capacity ◽  
Micro Milling ◽  
Fluid Viscosity ◽  
Low Reynolds Numbers ◽  
Milling Tool ◽  
Transmission Pipeline ◽  
Surface Patterns

High friction between a fluid and a pipe wall results in increased pumping requirements. This friction contributes to lower production rates and reduced system capacity. Thermal heating, fluid blending, and drag reducing agents (DRA) are commonly used methods for decreasing pressure drop in pipelines. Surface patterns inscribed onto internal pipe walls have also been shown to reduce fluid friction. In this paper, the effects of different surface patterns on the shear between a fluid and a wall are studied. Surfaces with different dimple patterns are investigated. Micro-dimpled patterns on the surface are created using an inclined, flat end micro-milling tool. The surfaces with different dimpled patterns are characterized and tested through morphological, contact angle, and viscosity measurement studies. The effects of the surface patterns are also studied through simulation. A Power Law relationship and apparent fluid viscosity is determined for the low Reynolds numbers investigated. The deepest dimpled surfaces investigated (0.2 mm dimple depth) result in a drag reduction of approximately 20% for silicone oil. Further research and application of the results to transmission pipeline systems are discussed.

Effect of Plenum Length and Diameter on Turbulent Heat Transfer in a Downstream Tube and on Plenum-Related Pressure Losses

1981 ◽  
Vol 103 (3) ◽  
pp. 415-422 ◽  
Author(s):  
S. C. Lau ◽  
E. M. Sparrow ◽  
J. W. Ramsey
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Loss ◽  
Reynolds Numbers ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
Turbulent Heat ◽  
Turbulent Regime ◽  
Transfer Coefficients ◽  
Pressure Loss Coefficient

A systematic experimental study was carried out to determine how the heat transfer characteristics of a turbulent tube flow are affected by the length and diameter of a cylindrical plenum chamber which delivers fluid to the tube. The net pressure loss due to the presence of the plenum was also measured. The experimental arrangement was such that the fluid experiences a consecutive expansion and contraction in the plenum before entering the electrically heated test section. Air was the working fluid, and the Reynolds number was varied over the range from 5,000 to 60,000. It was found that at axial stations in the upstream portion of the tube, there are substantially higher heat transfer coefficients in the presence of longer plenums. Thus, a longer plenum functions as an enhancement device. On the other hand, the plenum diameter appears to have only a minor influence in the range investigated (i.e., plenum diameters equal to three and six times the tube diameter). The fully developed Nusselt numbers are independent of the plenum length and diameter. With longer plenums in place, the thermal entrance length showed increased sensitivity to Reynolds number in the fully turbulent regime. The pressure loss coefficient, which compares the plenum-related pressure loss with the velocity head in the tube, increases more or less linearly with the plenum length. With regard to experimental technique, it was demonstrated that guard heating/cooling of the electrical bus adjacent to the tube inlet is necessary for accurate heat transfer results at low Reynolds numbers but, although desirable, is less necessary at higher Reynolds numbers.

An Experimental Investigation of Contoured Leading Edges for Secondary Flow Loss Reduction

2004 ◽  
Author(s):  
Sandor Becz ◽  
Mark S. Majewski ◽  
Lee S. Langston
Keyword(s):  
Secondary Flow ◽  
Pressure Loss ◽  
Total Pressure ◽  
Leading Edge ◽  
Loss Coefficient ◽  
Total Pressure Loss ◽  
Loss Reduction ◽  
Pressure Loss Coefficient ◽  
Flow Loss ◽  
Total Pressure Loss Coefficient

Experimental results are presented which provide mass averaged total pressure loss coefficient measurements for three different turbine airfoil leading edge configurations. A baseline (Langston) configuration, a leading edge bulb, and a leading edge fillet were tested in a large-scale, low aspect ratio, high turning linear cascade. Results show that while the fillet geometry reduced overall loss by approximately 7%, the bulb did not exhibit a loss reduction. For the fillet, overall turning was slightly reduced, while for the bulb turning increased slightly. Thus, the bulb shows potential for increasing airfoil loading without an associated loss penalty. Contour plots of total pressure loss coefficient and vorticity are presented for all geometries and the major differences between each are discussed. Through investigation of pitch averaged loss profiles it is found that the area of greatest reduction differs between the bulb and fillet, leading to the possibility that the mechanisms through which each is affecting the flow may be different. This provides hope that the best features of each may potentially be combined to determine an optimum shape for secondary flow loss reduction.

Pressure-Loss Coefficient of 90 deg Sharp-Angled Miter Elbows

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Wameedh T. M. Al-Tameemi ◽  
Pierre Ricco
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Pressure Loss ◽  
Dynamic Pressure ◽  
Reynolds Numbers ◽  
Loss Coefficient ◽  
Straight Pipe ◽  
Pressure Loss Coefficient ◽  
Circular Pipes ◽  
Piping Systems

The pressure drop across 90deg sharp-angled miter elbows connecting straight circular pipes is studied in a bespoke experimental facility by using water and air as working fluids flowing in the range of bulk Reynolds number 500<Re<60,000. To the best of our knowledge, the dependence on the Reynolds number of the pressure drop across the miter elbow scaled by the dynamic pressure, i.e., the pressure-loss coefficient K, is reported herein for the first time. The coefficient is shown to decrease sharply with the Reynolds number up to about Re=20,000 and, at higher Reynolds numbers, to approach mildly a constant K=0.9, which is about 20% lower than the currently reported value in the literature. We quantify this relation and the dependence between K and the straight-pipe friction factor at the same Reynolds number through two new empirical correlations, which will be useful for the design of piping systems fitted with these sharp elbows. The pressure drop is also expressed in terms of the scaled equivalent length, i.e., the length of a straight pipe that would produce the same pressure drop as the elbow at the same Reynolds number.

HEMODYNAMICS IN STENOSED ARTERIES — EFFECTS OF STENOSIS SHAPES

2010 ◽  
Vol 07 (03) ◽  
pp. 397-419 ◽  
Author(s):  
MOLOY K. BANERJEE ◽  
DEBABRATA NAG ◽  
RANJAN GANGULY ◽  
AMITAVA DATTA
Keyword(s):  
Pressure Loss ◽  
Reynolds Numbers ◽  
Loss Coefficient ◽  
Centerline Velocity ◽  
Hemodynamic Parameters ◽  
Gaussian Shape ◽  
Pressure Loss Coefficient ◽  
Flow Through ◽  
Recirculation Length ◽  
Hemodynamic Flow

A numerical analysis has been carried out to investigate the hemodynamic flow through stenosed arteries having mild (S = 25%) to severe (S = 65%) occlusions and under different regimes of flow Reynolds numbers ( Re ) ranging from 50 to 400. Influence of different stenosis shapes (rectangular, trapezoidal, cosine, and Gaussian) on key hemodynamic parameters e.g., recirculation length, wall shear stress (WSS), pressure drop, and irreversible pressure loss coefficient (C I ) are studied. It has been observed that for S = 25%, no flow separation takes place with cosine and Gaussian shaped stenoses for all the Re values considered, while for rectangular or trapezoidal shapes the flow begins to separate at Re = 400. At higher degrees of stenosis, post-stenotic recirculation is noticed for all the shapes considered — the largest recirculation length being observed with the rectangular shape. The peak centerline velocity in the stenosed region is more sensitive to a change in the degree of occlusion for rectangular stenosis than the other shapes. From the study, it is also revealed that the irreversible pressure loss coefficient (C I ) is the maximum for rectangular shaped stenosis, while it is the least for Gaussian shape. It is observed that at high Re regime, C I becomes insensitive to Re values and can be approximated to be a function of the degree of stenosis (S) and the stenosis shape only.

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