scholarly journals Influence of speed distribution in a rounded flow on the character of slopes erosion

2019 ◽  
Vol 20 (1) ◽  
pp. 85-95
Author(s):  
O. Ya. Maslikova ◽  
I. I. Gritsuk ◽  
D. N. Ionov ◽  
V. K. Debolskiy
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Hydraulic Structures ◽  
Natural Conditions ◽  
Channel Processes ◽  
Speed Distribution ◽  
Straight Line ◽  
River Hydraulics ◽  
Critical Reynolds Numbers ◽  
The Impact

One of the most important issues of river hydraulics is the movement of water and the formation of a channel in a stream that has a non-straight-line outline in the plan. Under natural conditions for rivers characteristic winding shape in the plan. The curvature of the jet occurs when the flow is divided into sleeves, at the inflow into the river, the confluence of flows, etc. Therefore, the study of channel processes in rivers is impossible without knowledge of the flow patterns at the curve of the channel. When designing hydraulic structures, including bridge crossings on the meandering sections of rivers, one should know the features of the dynamics of the channel in the sections of the flow turning. In winter, such areas may be narrowed due to the freezing of the channel, and during the period of ice thawing they are clogged with ice fragments. The narrowing of the canal causes an increase in the Reynolds number and a redistribution of velocity diagrams in the area under consideration, which causes a change in the erosion pattern. In laboratory conditions, the nature of the distribution of velocities and the formation of vortices on the installation, creating a rounded flow. It is shown that, at critical Reynolds numbers, a vortex countercurrent occurs in the rounded flow at the inner shore. The impact of this velocity distribution on the erosion pattern of the various slopes of the rounded flow was analyzed.

scholarly journals Blockage Correction and Reynolds Number Dependency of an Alpine Skier: A Comparison Between Two Closed-Section Wind Tunnels

Proceedings ◽  
2020 ◽  
Vol 49 (1) ◽  
pp. 19
Author(s):  
Ola Elfmark ◽  
Robert Reid ◽  
Lars Morten Bardal
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Absolute Error ◽  
Reynolds Numbers ◽  
Correction Method ◽  
Wind Tunnels ◽  
Alpine Skier ◽  
Blockage Correction ◽  
Reynolds Number Dependency ◽  
The Impact

The purpose of this study was to investigate the impact of blockage effect and Reynolds Number dependency by comparing measurements of an alpine skier in standardized positions between two wind tunnels with varying blockage ratios and speed ranges. The results indicated significant blockage effects which need to be corrected for accurate comparison between tunnels, or for generalization to performance in the field. Using an optimized blockage constant, Maskell’s blockage correction method improved the mean absolute error between the two wind tunnels from 7.7% to 2.2%. At lower Reynolds Numbers (<8 × 105, or approximately 25 m/s in this case), skier drag changed significantly with Reynolds Number, indicating the importance of testing at competition specific wind speeds. However, at Reynolds Numbers above 8 × 105, skier drag remained relatively constant for the tested positions. This may be advantageous when testing athletes from high speed sports since testing at slightly lower speeds may not only be safer, but may also allow the athlete to reliably maintain difficult positions during measurements.

Strut Interference Effects on Pitot Tube Velocity Measurements

2007 ◽  
Author(s):  
Sandra K. S. Boetcher ◽  
Ephraim M. Sparrow
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
The Body ◽  
Pitot Tube ◽  
Velocity Measurements ◽  
Measuring Device ◽  
Number Range ◽  
Low Reynolds Numbers ◽  
Velocity Measuring ◽  
The Impact

The possible impact of the presence of the strut portion of a Pitot tube on the efficacy of the tube as a velocity-measuring device has been evaluated by numerical simulation. At sufficiently low Reynolds numbers, there is a possibility that the precursive effects of the strut could alter the flow field adjacent to the static taps on the body of the Pitot tube and might even affect the impact pressure measured at the nose. The simulations were performed in dimensionless form with the Reynolds number being the only prescribed parameter, but the dimensions were taken from a short-shanked Pitot tube. Over the Reynolds number range from 1500 to 4000, a slight effect of the strut was identified. However, the variation due to the presence of the shank of the velocity measured by the Pitot tube operating in that range of Reynolds numbers was only 1.5%.

On the force fluctuations acting on a circular cylinder in crossflow from subcritical up to transcritical Reynolds numbers

1983 ◽  
Vol 133 ◽  
pp. 265-285 ◽  
Author(s):  
Günter Schewe
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Dynamic Range ◽  
Reynolds Numbers ◽  
Band Spectrum ◽  
Transitional Region ◽  
Force Measurements ◽  
Unsteady Forces ◽  
Number Range ◽  
Critical Reynolds Numbers

Force measurements were conducted in a pressurized wind tunnel from subcritical up to transcritical Reynolds numbers 2.3 × 104[les ]Re[les ] 7.1 × 106without changing the experimental arrangement. The steady and unsteady forces were measured by means of a piezobalance, which features a high natural frequency, low interferences and a large dynamic range. In the critical Reynolds-number range, two discontinuous transitions were observed, which can be interpreted as bifurcations at two critical Reynolds numbers. In both cases, these transitions are accompanied by critical fluctuations, symmetry breaking (the occurrence of a steady lift) and hysteresis. In addition, both transitions were coupled with a drop of theCDvalue and a jump of the Strouhal number. Similar phenomena were observed in the upper transitional region between the super- and the transcritical Reynolds-number ranges. The transcritical range begins at aboutRe≈ 5 × 106, where a narrow-band spectrum is formed withSr(Re= 7.1 × 106) = 0.29.

The Stability of Water Flow Over Heated and Cooled Flat Plates

1968 ◽  
Vol 90 (1) ◽  
pp. 109-114 ◽  
Author(s):  
Ahmed R. Wazzan ◽  
T. Okamura ◽  
A. M. O. Smith
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Stream Temperature ◽  
Heated Wall ◽  
Flat Plates ◽  
Critical Reynolds Numbers ◽  
The Stability ◽  
Sommerfeld Equation

The theory of two-dimensional instability of laminar flow of water over solid surfaces is extended to include the effects of heat transfer. The equation that governs the stability of these flows to Tollmien-Schlichting disturbances is the Orr-Sommerfeld equation “modified” to include the effect of viscosity variation with temperature. Numerical solutions to this equation at high Reynolds numbers are obtained using a new method of integration. The method makes use of the Gram-Schmidt orthogonalization technique to obtain linearly independent solutions upon numerically integrating the “modified Orr-Sommerfeld” equation using single precision arithmetic. The method leads to satisfactory answers for Reynolds numbers as high as Rδ* = 100,000. The analysis is applied to the case of flow over both heated and cooled flat plates. The results indicate that heating and cooling of the wall have a large influence on the stability of boundary-layer flow in water. At a free-stream temperature of 60 deg F and wall temperatures of 60, 90, 120, 135, 150, 200, and 300deg F, the critical Reynolds numbers Rδ* are 520, 7200, 15200, 15600, 14800, 10250, and 4600, respectively. At a free-stream temperature of 200F and wall temperature of 60 deg F (cooled case), the critical Reynolds number is 151. Therefore, it is evident that a heated wall has a stabilizing effect, whereas a cooled wall has a destabilizing effect. These stability calculations show that heating increases the critical Reynolds number to a maximum value (Rδ* max = 15,700 at a temperature of TW = 130 deg F) but that further heating decreases the critical Reynolds number. In order to determine the influence of the viscosity derivatives upon the results, the critical Reynolds number for the heated case of T∞ = 40 and TW = 130 deg F was determined using (a) the Orr-Sommerfeld equation and (b) the present governing equation. The resulting critical Reynolds numbers are Rδ* = 140,000 and 16,200, respectively. Therefore, it is concluded that the terms pertaining to the first and second derivatives of the viscosity have a considerable destabilizing influence.

The Role of Reynolds Number Effect and Tip Leakage in Compressor Geometry Scaling at Low Turbulent Reynolds Numbers

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Markus Diehl ◽  
Christoph Schreiber ◽  
Jürg Schiffmann
Keyword(s):  
Reynolds Number ◽  
Surface Friction ◽  
Reynolds Numbers ◽  
Small Scale ◽  
Tip Leakage ◽  
Reynolds Number Effect ◽  
Geometric Scaling ◽  
Compressor Performance ◽  
The Impact

Abstract In compressor design, a convenient way to save time is to scale an existing geometry to required specifications, rather than developing a new design. The approach works well when scaling compressors of similar size at high Reynolds numbers but becomes more complex when applied to small-scale machines. Besides the well-understood increase in surface friction due to increased relative surface roughness, two other main problems specific to small-scale turbomachinery can be specified: (1) the Reynolds number effect, describing the non-linear dependency of surface friction on Reynolds number and (2) increased relative tip clearance resulting from manufacturing limitations. This paper investigates the role of both effects in a geometric scaling process, as used by a designer. The work is based on numerical models derived from an experimentally validated geometry. First, the effects of geometric scaling on compressor performance are assessed analytically. Second, prediction capabilities of reduced-order models from the public domain are assessed. In addition to design point assessment, often found in other publications, the models are tested at off-design. Third, the impact of tip leakage on compressor performance and its Reynolds number dependency is assessed. Here, geometries of different scale and with different tip clearances are investigated numerically. Fourth, a detailed investigation regarding tip leakage driving mechanisms is carried out and design recommendations to improve small-scale compressor performance are provided.

Aerodynamic Loading Distribution Effects on Off-Design Performance of Highly Loaded LP Turbine Cascades Under Steady and Unsteady Incoming Flows

2016 ◽  
Author(s):  
Marco Berrino ◽  
Daniele Simoni ◽  
Marina Ubaldi ◽  
Pietro Zunino ◽  
Francesco Bertini
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Incidence Angle ◽  
Reynolds Numbers ◽  
Angle Variation ◽  
Aerodynamic Loading ◽  
Profile Losses ◽  
Unsteady Inflow ◽  
The Impact ◽  
Highly Loaded

The present work is part of a continuous cooperation between GE AvioAero and the University of Genova aimed at understanding the detailed flow physics of efficient highly loaded LPT blades for aeroengine applications. In this paper the effects of the aerodynamic loading distribution on the performances of three different cascades with the same Zweifel number have been experimentally investigated under steady and unsteady incoming flow conditions. Measurements have been carried out for several Reynolds numbers (in the range 70000<Re<300000) with an incidence angle variation of ±9°, in order to cover the typical realistic LP aeroengine turbine working range on design and off-design conditions. Profile aerodynamic loadings and total pressure loss coefficients have been evaluated for the different cases. Efficiency data clearly highlight that at nominal incidence an aft loaded cascade provides the lowest profile losses when the boundary layer is attached to the wall, as it occurs in the unsteady case or at high Reynolds numbers. Only at the lowest Reynolds number in the steady case, a front loaded profile is preferable since it helps to prevent a laminar boundary layer separation. Moreover, the aft loaded profile has also shown a better robustness to incidence angle variation, both for the steady and the unsteady inflow conditions. Indeed, the growth of profile losses with incidence is weaker for the aft loaded cascade with respect to the front and the mid loaded ones. However, irrespective of the loading distribution the loss trend vs incidence angle has been found to be completely different between the steady and the unsteady operations. Results in the paper give a clear overview of the impact of the loading distribution on profile losses as a function of Reynolds number, as well as a detailed view of the influence due to the loading characteristics on incidence robustness under the realistic unsteady inflow case.

Scaling of Film Cooling Performance From Ambient to Engine Temperatures

2014 ◽  
Author(s):  
Nathan J. Greiner ◽  
Marc D. Polanka ◽  
James L. Rutledge
Keyword(s):  
Reynolds Number ◽  
High Temperature ◽  
Prandtl Number ◽  
Film Cooling ◽  
Reynolds Numbers ◽  
Performance Measurements ◽  
Ambient Conditions ◽  
Cooling Performance ◽  
Ambient Temperatures ◽  
The Impact

The present study employs Computational Fluid Dynamics (CFD) to explore the complexities of scaling film cooling performance measurements from ambient laboratory conditions to high temperature engine conditions. In this investigation, a single shaped hole is examined computationally at both engine and near ambient temperatures to understand the impact of temperature dependent properties on scaling film cooling performance. By varying select flow and thermal parameters for the low temperature cases and comparing the results to high temperature flow, the parameters which must be matched to scale film cooling performance are determined. The results show that only matching the density and mass flux ratios is insufficient for scaling to high temperatures. In accordance with convective heat transfer fundamentals, freestream and coolant Reynolds numbers and Prandtl numbers must also be matched to obtain scalable results. By virtue of the Prandtl number for air remaining nearly constant with temperature, the Prandtl number at ambient conditions is sufficiently matched to engine temperatures. However, laboratory limitations can prevent matching both the freestream and coolant Reynolds numbers simultaneously. By examining this trade-off, it is determined that matching the coolant Reynolds number produces the best scalability. It is also found that by averaging the adiabatic effectiveness of two experiments in which the freestream and coolant Reynolds number are matched respectively results in significantly better scalability for cases with a separated coolant jet.

Transonic Turbine Cascade Measurements for a Variable Speed Power Turbine Blade at Low to Moderate Reynolds Numbers: Aerodynamic Loss Surveys

2015 ◽  
Author(s):  
J. A. Long ◽  
L. P. G. Moualeu ◽  
N. J. Hemming ◽  
F. E. Ames ◽  
Y. B. Suzen
Keyword(s):  
Reynolds Number ◽  
Turbine Blade ◽  
Total Pressure ◽  
Reynolds Numbers ◽  
Turbulence Level ◽  
Variable Speed ◽  
Aerodynamic Loss ◽  
Power Turbine ◽  
The Impact ◽  
Aerodynamic Losses

The influence of low to moderate Reynolds number and low to moderate turbulence level on aerodynamic losses is investigated in an incidence tolerant turbine blade cascade for a variable speed power turbine. This work complements midspan heat transfer and blade loading measurements which are acquired in the same cascade at the same conditions. The aerodynamic loss measurements are acquired to quantify the influence of Reynolds number and turbulence level on blade loss buckets over the wide range of incidence angles for the variable speed turbine. Eight discrete incidence angles are investigated ranging from +5.8° to −51.2°. Noting that the design inlet angle of the blade is 34.2° these incidence angles correspond to inlet angles ranging from +40° to −17°. Exit loss surveys, presented in terms of local total pressure loss and secondary velocities have been acquired at four exit chord Reynolds numbers ranging from 50,000 to 568,000. These measurements were acquired at both low (∼0.4%) and moderate (∼4.0%) inlet turbulence intensities. The total pressure losses are also presented in terms of cross passage averaged loss and turning angle. The resulting loss buckets for passage averaged losses are plotted at varied Reynolds numbers and turbulence condition. The exit loss data quantify the impact of Reynolds number and incidence angle on aerodynamic losses. Generally, these data document the substantial deterioration of performance with decreasing Reynolds number.

Analysis and Experimental Visualization of the Flow Behavior Between Parallel Separated Cross-Corrugated Plates

2009 ◽  
Author(s):  
J. M. Luna ◽  
R. Romero-Mendez ◽  
A. Hernandez-Guerrero ◽  
J. L. Luviano-Ortiz
Keyword(s):  
Reynolds Number ◽  
Flow Direction ◽  
Flow Behavior ◽  
Essential Feature ◽  
Reynolds Numbers ◽  
Chaotic Mixing ◽  
Micro Particles ◽  
Critical Reynolds Numbers ◽  
Corrugated Plates ◽  
Channel Configuration

The experimental visualization of the flow patterns developed in a channel formed by parallel separated cross-corrugated plates is presented in this work. The flow visualization was carried out by seeding reflective micro-particles in water. The cross-corrugated plates were characterized by corrugations with sinusoidal profile, 0.083 m wavelength and 0.075 m amplitude, placed at ±45° relative to the main flow direction. While the wavelength-amplitude aspect ratio was kept fixed, both the uniform spacing between plates and Reynolds number were varied. The essential feature of the flow is the secondary swirling motion developed by the furrow flows because of the crossing among streams. Three flow regimes were found: steady, unsteady and chaotic mixing. At some critical Reynolds numbers, depending upon the separation between plates, the flow becomes unsteady and chaotic mixing appears first in the outlet of the channel. Chaotic mixing moves closer to the inlet of the channel as the Reynolds number is increased. The results show that the onset of chaotic mixing occurs at larger Reynolds numbers as the spacing is increased. The flow pattern of this channel configuration is compared to that reported for the chevron arrangement.

Linear instability of lid- and pressure-driven flows in channels textured with longitudinal superhydrophobic grooves

2021 ◽  
Vol 932 ◽  
Author(s):  
Samuel D. Tomlinson ◽  
Demetrios T. Papageorgiou
Keyword(s):  
Reynolds Number ◽  
Unstable Mode ◽  
Reynolds Numbers ◽  
Linear Instability ◽  
Large Reynolds Number ◽  
Spanwise Direction ◽  
Channel Height ◽  
Critical Reynolds Numbers ◽  
Upper Lid ◽  
Pressure Driven

It is known that an increased flow rate can be achieved in channel flows when smooth walls are replaced by superhydrophobic surfaces. This reduces friction and increases the flux for a given driving force. Applications include thermal management in microelectronics, where a competition between convective and conductive resistance must be accounted for in order to evaluate any advantages of these surfaces. Of particular interest is the hydrodynamic stability of the underlying basic flows, something that has been largely overlooked in the literature, but is of key relevance to applications that typically base design on steady states or apparent-slip models that approximate them. We consider the global stability problem in the case where the longitudinal grooves are periodic in the spanwise direction. The flow is driven along the grooves by either the motion of a smooth upper lid or a constant pressure gradient. In the case of smooth walls, the former problem (plane Couette flow) is linearly stable at all Reynolds numbers whereas the latter (plane Poiseuille flow) becomes unstable above a relatively large Reynolds number. When grooves are present our work shows that additional instabilities arise in both cases, with critical Reynolds numbers small enough to be achievable in applications. Generally, for lid-driven flows one unstable mode is found that becomes neutral as the Reynolds number increases, indicating that the flows are inviscidly stable. For pressure-driven flows, two modes can coexist and exchange stability depending on the channel height and slip fraction. The first mode remains unstable as the Reynolds number increases and corresponds to an unstable mode of the two-dimensional Rayleigh equation, while the second mode becomes neutrally stable at infinite Reynolds numbers. Comparisons of critical Reynolds numbers with the experimental observations for pressure-driven flows of Daniello et al. (Phys. Fluids, vol. 21, issue 8, 2009, p. 085103) are encouraging.

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