The Effect of Reynolds Number on the Performance of a Tangential-Flow Turbine

1965 ◽  
Author(s):  
Robert G. Adams
Keyword(s):  
Reynolds Number ◽  
Power Systems ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Theoretical Determination ◽  
Low Reynolds Numbers ◽  
Tangential Flow ◽  
Circulatory Flow ◽  
Reasonable Prediction

The tangential-flow turbine, which was developed from the drag turbine in an effort to take advantage of the circulatory flow in the drag-turbine passages, frequently has been proposed for use in power systems characterized by low specific speeds. Since such systems often operate with low exhaust pressures which lead to low Reynolds numbers in turbine passages, it is of interest to determine the effect of Reynolds number on the performance of this type of machine. Theoretical determination of the effect is made difficult by the complex three-dimensional nature of the flow in this type of turbine. This paper describes a program of tests which was run on a tangential-flow turbine to investigate the effect of Reynolds number, and presents a simplified theoretical approach to the Reynolds-number effect which is shown to give a reasonable prediction of the trend of the effect.

Experimental characterization of three-dimensional corner flows at low Reynolds numbers

2012 ◽  
Vol 707 ◽  
pp. 37-52 ◽  
Author(s):  
J. Sznitman ◽  
L. Guglielmini ◽  
D. Clifton ◽  
D. Scobee ◽  
H. A. Stone ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Channel Cross Section ◽  
Experimental Characterization ◽  
Low Reynolds Numbers ◽  
Low Reynolds

AbstractWe investigate experimentally the characteristics of the flow field that develops at low Reynolds numbers ($\mathit{Re}\ll 1$) around a sharp $9{0}^{\ensuremath{\circ} } $ corner bounded by channel walls. Two-dimensional planar velocity fields are obtained using particle image velocimetry (PIV) conducted in a towing tank filled with a silicone oil of high viscosity. We find that, in the vicinity of the corner, the steady-state flow patterns bear the signature of a three-dimensional secondary flow, characterized by counter-rotating pairs of streamwise vortical structures and identified by the presence of non-vanishing transverse velocities (${u}_{z} $). These results are compared to numerical solutions of the incompressible flow as well as to predictions obtained, for a similar geometry, from an asymptotic expansion solution (Guglielmini et al., J. Fluid Mech., vol. 668, 2011, pp. 33–57). Furthermore, we discuss the influence of both Reynolds number and aspect ratio of the channel cross-section on the resulting secondary flows. This work represents, to the best of our knowledge, the first experimental characterization of the three-dimensional flow features arising in a pressure-driven flow near a corner at low Reynolds number.

On High-Performance Airfoil at Very Low Reynolds Number

2016 ◽  
Vol 28 (3) ◽  
pp. 273-285
Author(s):  
Katsuya Hirata ◽  
◽  
Ryo Nozawa ◽  
Shogo Kondo ◽  
Kazuki Onishi ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Flat Plate ◽  
High Performance ◽  
Low Reynolds Number ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Slow Flow ◽  
Low Reynolds Numbers ◽  
Low Reynolds

[abstFig src='/00280003/02.jpg' width=""300"" text='Iso-Q surfaces of very-slow flow past an iNACA0015' ] The airfoil is often used as the elemental device for flying/swimming robots, determining its basic performances. However, most of the aerodynamic characteristics of the airfoil have been investigated at Reynolds numbers Re’s more than 106. On the other hand, our knowledge is not enough in low Reynolds-number ranges, in spite of the recent miniaturisation of robots. In the present study, referring to our previous findings (Hirata et al., 2011), we numerically examine three kinds of high-performance airfoils proposed for very-low Reynolds numbers; namely, an iNACA0015 (the NACA0015 placed back to front), an FPBi (a flat plate blended with iNACA0015 as its upper half) and an FPBN (a flat plate blended with the NACA0015 as its upper half), in comparison with such basic airfoils as a NACA0015 and an FP (a flat plate), at a Reynolds number Re = 1.0 × 102 using two- and three-dimensional computations. As a result, the FPBi shows the best performance among the five kinds of airfoils.

Flow separation on a spheroid at incidence

1979 ◽  
Vol 92 (4) ◽  
pp. 643-657 ◽  
Author(s):  
Taeyoung Han ◽  
V. C. Patel
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Inviscid Flow ◽  
Reynolds Numbers ◽  
Surface Flow ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Turbulent Separation

Surface streamline patterns on a spheroid have been examined at several angles of attack. Most of the tests were performed at low Reynolds numbers in a hydraulic flume using coloured dye to make the surface flow visible. A limited number of experiments was also carried out in a wind tunnel, using wool tufts, to study the influence of Reynolds number and turbulent separation. The study has verified some of the important qualitative features of three-dimensional separation criteria proposed earlier by Maskell, Wang and others. The observed locations of laminar separation lines on a spheroid at various incidences have been compared with the numerical solutions of Wang and show qualitative agreement. The quantitative differences are attributed largely to the significant viscous-inviscid flow interaction which is present, especially at large incidences.

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.

An Investigation of Factors Influencing the Calibration of Five-Hole Probes for Three-Dimensional Flow Measurements

1993 ◽  
Vol 115 (3) ◽  
pp. 513-519 ◽  
Author(s):  
R. G. Dominy ◽  
H. P. Hodson
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Flow Measurements ◽  
Low Reynolds Numbers ◽  
Additional Information ◽  
Reynolds Number Effects ◽  
Low Speed Wind Tunnel ◽  
Probe Head

The effects of Reynolds number, Mach number, and turbulence on the calibrations of commonly used types of five-hole probe are discussed. The majority of the probes were calibrated at the exit from a transonic nozzle over a range of Reynolds numbers (7 × 103 < Re < 80 × 103 based on probe tip diameter) at subsonic and transonic Mach numbers. Additional information relating to the flow structure were obtained from a large-scale, low-speed wind tunnel. The results confirmed the existence of two distinct Reynolds number effects. Flow separation around the probe head affects the calibrations at relatively low Reynolds numbers while changes in the detailed structure of the flow around the sensing holes affects the calibrations even when the probe is nulled. Compressibility is shown to have little influence upon the general behavior of these probes in terms of Reynolds number sensitivity but turbulence can affect the reliability of probe calibrations at typical test Reynolds numbers.

Simulations of Flow and Mass Transfer in a Passive Micromixer

2011 ◽  
Author(s):  
Hamid Farangis Zadeh ◽  
Arash Marahel
Keyword(s):  
Reynolds Number ◽  
Three Dimensional ◽  
Main Idea ◽  
Contact Layer ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Low Reynolds Numbers ◽  
Passive Micromixer ◽  
Simulation Results ◽  
Dimensional Simulation

We present three-dimensional simulation results regarding performance of a novel planar passive micromixer functioning at low Reynolds numbers. A combination of folding and contracting of microchannels is the main idea for designing of an effective, easy-to-produce, and non-expensive micromixer. The simulation results show that, depend on Reynolds number, centrifugal forces can generate different secondary flows and Dean vortices after each bend. Consequently, the thickness and the form of the contact layer between fluids become strongly affected. The simulation process is repeated for different Reynolds numbers from 10 to 100, and we observe that the maximum and minimum mixing efficiencies at the output channel are related to Reynolds number 60 and 80, respectively.

Computational Investigation of the Three-Dimensional Flow Structure and Losses in a Low Reynolds Number Microturbine

2011 ◽  
Author(s):  
M. Omri ◽  
L. G. Fre´chette
Keyword(s):  
Reynolds Number ◽  
Heat Engine ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Tip Clearance ◽  
3D Flow ◽  
Low Reynolds Numbers ◽  
Blade Passage ◽  
Low Reynolds

In this work, three dimensional numerical studies of the aerodynamics in laminar subsonic cascades at relatively low Reynolds numbers (Re < 2500) are presented. The stator and rotor blade designs are those for a MEMS-based Rankine microturbine power-plant-on-a-chip with 100 micron chord blades. Blade passage calculations in 2D and 3D were done for different Reynolds numbers, four different tip clearances (0%, 5%, 10% and 20%) and four incidences (0°, 5°, 10° and 15°) to determine the flow patterns and compute losses. These conditions are applied to a blade passage without rotation (stator) and with rotation (rotor), both for a stationary and moving outer casing. The 3D blade passage (without tip clearance) indicates the presence of two large symmetric vortices due to the interaction between flow curvature and hub/casing boundary layers. With tip clearance, a secondary vortex appears due to tip flow. This so-called tip vortex becomes dominant in the case of tip clearance above 10%. Relative wall motion also impacts the 3D flow patterns due to the important tangential drag at these low Reynolds numbers. Two dimensional calculations characterize well the flow at the mid-height plane, but are not sufficient for loss predictions due to the omission of the 3D flow structures. The 3D total losses increase dramatically for Re<500, which is similar to 2D studies. This suggests an operating Reynolds number greater than this to obtain efficiency levels necessary to operate a heat engine. The losses also increased monotonically with increasing tip clearance and incidence.

scholarly journals Characteristics of an Annular Turbine Cascade at Low Reynolds Numbers

1998 ◽  
Author(s):  
Takayuki Matsunuma ◽  
Hiroyuki Abe ◽  
Yasukata Tsutsui ◽  
Koji Murata
Keyword(s):  
Reynolds Number ◽  
Gas Turbines ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Boundary Layer Separation ◽  
Aerodynamic Characteristics ◽  
Secondary Flows ◽  
Suction Surface ◽  
Low Reynolds Numbers ◽  
Low Reynolds

The aerodynamic characteristics of turbine cascades are thought to be relatively satisfactory due to the favorable pressure gradient of the accelerating flow. But within the low Reynolds number region of approximately 6×104 where the 300kW ceramic gas turbines which are being developed under the New Sunshine Project of Japan operate, the characteristics such as boundary layer separation, reattachment and secondary flow which lead to prominent power losses can not be easily predicted. In this research, experiments have been conducted to evaluate the performance of an annular turbine stator cascade. Wakes of the cascade were measured using a single hot wire and five hole pressure tube, for a range of blade chord Reynolds numbers based on the inlet condition from 2×104 to 12×104. Flow visualizations on the suction surface of the blade were carried out using oil film method. At low Reynolds numbers, the flow structure in the annular cascade was quite complex and three-dimensional. The separation line on the suction surface moved upstream due to the decrease of Reynolds number. In addition, the growth of secondary flows, i.e., passage vortices and leakage vortex, was extremely under the influence of Reynolds number.

Quasi-periodic cylinder wakes and the Ginzburg–Landau model

1995 ◽  
Vol 291 ◽  
pp. 191-222 ◽  
Author(s):  
Pierre Albarède ◽  
Michel Provansal
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Model Parameters ◽  
Ginzburg Landau ◽  
Phase Measurements ◽  
Low Reynolds Numbers ◽  
Aspect Ratios ◽  
Second Mode ◽  
Time Periodic

The time-periodic phenomena occurring at low Reynolds numbers (Re [lsim ] 180) in the wake of a circular cylinder (finite-length section) are well modelled by a Ginzburg–Landau (GL) equation with zero boundary conditions (Albarède & Monkewitz 1992). According to the GL model, the wake is mainly governed by a rescaled length, based on the aspect ratio and the Reynolds number. However, the determination of coefficients is not complete: we correct a former evaluation of the nonlinear Landau coefficient, we show difficulties in obtaining a consistent set of coefficients for different Reynolds numbers or end configurations, and we propose the use of an ‘influential’ length. New two-point velocimetry results are presented: phase measurements show that a subtle property is shared by the three-dimensional wake and the GL model.Two time-quasi-periodic phenomena – the second mode observed for smaller aspect ratios, and the dislocated chevron observed for larger aspect ratios – are presented and precisely related to the GL model. Only the linear characteristics of the second mode are readily explained; its existence depends on the end conditions. Moreover, through a quasi-static variation of the length, the second mode evolves continuously to end cells (and vice versa). Observations of the dislocated chevron are recalled. A very similar instability is found on the chevron solution of the GL equation, when the model parameters (c1, c2) move towards the phase diffusion unstable region. The early stages of this instability are qualitatively similar to the observed patterns.

scholarly journals The Effect of the Reynolds Number on the Three-Dimensional Flow in a Straight Compressor Cascade

1988 ◽  
Author(s):  
Václav Cyrus
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Compressor Cascade ◽  
Simple Correlation ◽  
Three Dimensional Flow ◽  
Flow Angle ◽  
Low Reynolds Numbers ◽  
Dimensional Flow

A straight compressor cascade of aspect ratio 2 was tested in a low speed tunnel within Reynolds number Re1 = 45 000 – 150 000 and inlet flow angle α1 = 35° – 48°. The profile of the blade was NACA 65-12-10. The purpose of the paper was to obtain data on three–dimensional flow in a straight cascade at low Reynolds numbers. Some experimental results on secondary flow have been made into simple correlation relations.

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