scholarly journals Investigation on the Drag Coefficient of the Steady and Unsteady Flow Conditions in Coarse Porous Media

2021 ◽  
Author(s):  
Hadi Norouzi ◽  
Jalal Bazargan ◽  
Faezah Azhang ◽  
Rana Nasiri
Keyword(s):  
Reynolds Number ◽  
Porous Media ◽  
Friction Coefficient ◽  
Unsteady Flow ◽  
Drag Coefficient ◽  
Flow Velocity ◽  
Hydraulic Gradient ◽  
Flow Conditions ◽  
Porous Media Equations ◽  
Unsteady Flow Condition

Abstract The study of the steady and unsteady flow through porous media and the interactions between fluids and particles is of utmost importance. In the present study, binomial and trinomial equations to calculate the changes in hydraulic gradient (i) in terms of flow velocity (V) were studied in the steady and unsteady flow conditions, respectively. According to previous studies, the calculation of drag coefficient (Cd) and consequently, drag force (Fd) is a function of coefficient of friction (f). Using Darcy-Weisbach equations in pipes, the hydraulic gradient equations in terms of flow velocity in the steady and unsteady flow conditions, and the analytical equations proposed by Ahmed and Sunada in calculation of the coefficients a and b of the binomial equation and the friction coefficient (f) equation in terms of the Reynolds number (Re) in the porous media, equations were presented for calculation of the friction coefficient in terms of the Reynolds number in the steady and unsteady flow conditions in 1D (one-dimensional) confined porous media. Comparison of experimental results with the results of the proposed equation in estimation of the drag coefficient in the present study confirmed the high accuracy and efficiency of the equations. The mean relative error (MRE) between the computational (using the proposed equations in the present study) and observational (direct use of experimental data) friction coefficient for small, medium and large grading in the steady flow conditions was equal to 1.913, 3.614 and 3.322%, respectively. In the unsteady flow condition, the corresponding values of 7.806, 14.106 and 10.506 % were obtained, respectively.

scholarly journals Investigation on the Drag Coefficient of the Steady and Unsteady Flow Conditions in Coarse Porous Media

2021 ◽  
Author(s):  
Hadi Norouzi ◽  
Jalal Bazargan ◽  
Faezah Azhang ◽  
Rana Nasiri
Keyword(s):  
Reynolds Number ◽  
Porous Media ◽  
Friction Coefficient ◽  
Unsteady Flow ◽  
Drag Coefficient ◽  
Flow Velocity ◽  
Hydraulic Gradient ◽  
Flow Conditions ◽  
Porous Media Equations ◽  
Unsteady Flow Condition

Abstract The study of the steady and unsteady flow through porous media and the interactions between fluids and particles is of utmost importance. In the present study, binomial and trinomial equations to calculate the changes in hydraulic gradient (i) in terms of flow velocity (V) were studied in the steady and unsteady flow conditions, respectively. According to previous studies, the calculation of drag coefficient (Cd) and consequently, drag force (Fd) is a function of coefficient of friction (f). Using Darcy-Weisbach equations in pipes, the hydraulic gradient equations in terms of flow velocity in the steady and unsteady flow conditions, and the analytical equations proposed by Ahmed and Sunada in calculation of the coefficients a and b of the binomial equation and the friction coefficient (f) equation in terms of the Reynolds number (Re) in the porous media, equations were presented for calculation of the friction coefficient in terms of the Reynolds number in the steady and unsteady flow conditions in 1D (one-dimensional) confined porous media. Comparison of experimental results with the results of the proposed equation in estimation of the drag coefficient in the present study confirmed the high accuracy and efficiency of the equations. The mean relative error (MRE) between the computational (using the proposed equations in the present study) and observational (direct use of experimental data) friction coefficient for small, medium and large grading in the steady flow conditions was equal to 1.913, 3.614 and 3.322%, respectively. In the unsteady flow condition, the corresponding values of 7.806, 14.106 and 10.506 % were obtained, respectively.

Computational Study of the Risø-B1-18 Airfoil with a Hinged Flap Providing Variable Trailing Edge Geometry

2005 ◽  
Vol 29 (2) ◽  
pp. 89-113 ◽  
Author(s):  
Niels Troldborg
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Computational Study ◽  
Turbine Blades ◽  
Aerodynamic Characteristics ◽  
Flow Conditions ◽  
Wind Turbine Blades ◽  
Trailing Edge ◽  
Edge Geometry ◽  
Fully Developed Turbulent Flow

A comprehensive computational study, in both steady and unsteady flow conditions, has been carried out to investigate the aerodynamic characteristics of the Risø-B1-18 airfoil equipped with variable trailing edge geometry as produced by a hinged flap. The function of such flaps should be to decrease fatigue-inducing oscillations on the blades. The computations were conducted using a 2D incompressible RANS solver with a k-w turbulence model under the assumption of a fully developed turbulent flow. The investigations were conducted at a Reynolds number of Re = 1.6 · 106. Calculations conducted on the baseline airfoil showed excellent agreement with measurements on the same airfoil with the same specified conditions. Furthermore, a more widespread comparison with an advanced potential theory code is presented. The influence of various key parameters, such as flap shape, flap size and oscillating frequencies, was investigated so that an optimum design can be suggested for application with wind turbine blades. It is concluded that a moderately curved flap with flap chord to airfoil curve ratio between 0.05 and 0.10 would be an optimum choice.

Experimental Study on the Piping Erosion Mechanism of Gap-Graded Soils Under a Supercritical Hydraulic Gradient

2021 ◽  
Author(s):  
Liang Chen ◽  
Yu Wan ◽  
Jian-Jian He ◽  
Chun-Mu Luo ◽  
Shu-fa Yan ◽  
...  
Keyword(s):  
Hydraulic Conductivity ◽  
Unsteady Flow ◽  
Relative Density ◽  
Flow Velocity ◽  
Steady Flow ◽  
Fine Particle ◽  
Failure Process ◽  
Hydraulic Gradient ◽  
Particle Content ◽  
Piping Erosion

Abstract Seepage-induced piping erosion is observed in many geotechnical structures. This paper studies the piping mechanism of gap-graded soils during the whole piping erosion failure process under a supercritical hydraulic gradient. We define the supercritical ratio Ri and study the change in the parameters such as the flow velocity, hydraulic conductivity, and fine particle loss with Ri. Under steady flow, a formula for determining the flow velocity state of the sample with Ri according to the fine particle content and relative density of the sample was proposed; during the piping failure process, the influence of Rimax on the rate at which the flow velocity and hydraulic conductivity of the sample increase as Ri decreases was greater than that of the initial relative density and the initial fine particle content of the sample. Under unsteady flow, a larger initial relative density corresponds to a smaller amplitude of increase in the average value of the peak flow velocity with increasing Ri. Compared with the test under steady flow, the flow velocity under unsteady flow would experience abrupt changes. The relative position of the trend line L of the flow velocity varying with Ri under unsteady flow and the fixed peak water head height point A under steady flow were related to the relative density of the sample.

Unsteady flow about a sphere at low to moderate Reynolds number. Part 1. Oscillatory motion

1994 ◽  
Vol 277 ◽  
pp. 347-379 ◽  
Author(s):  
Eugene J. Chang ◽  
Martin R. Maxey
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Steady Flow ◽  
Oscillatory Flow ◽  
Reynolds Numbers ◽  
Oscillatory Motion ◽  
Rigid Sphere ◽  
Flow Conditions ◽  
Steady Streaming ◽  
Moderate Reynolds Number

A direct numerical simulation, based on spectral methods, has been used to compute the time-dependent, axisymmetric viscous flow past a rigid sphere. An investigation has been made for oscillatory flow about a zero mean for different Reynolds numbers and frequencies. The simulation has been verified for steady flow conditions, and for unsteady flow there is excellent agreement with Stokes flow theory at very low Reynolds numbers. At moderate Reynolds numbers, around 20, there is good general agreement with available experimental data for oscillatory motion. Under steady flow conditions no separation occurs at Reynolds number below 20; however in an oscillatory flow a separation bubble forms on the decelerating portion of each cycle at Reynolds numbers well below this. As the flow accelerates again the bubble detaches and decays, while the formation of a new bubble is inhibited till the flow again decelerates. Steady streaming, observed for high frequencies, is also observed at low frequencies due to the flow separation. The contribution of the pressure to the resultant force on the sphere includes a component that is well described by the usual added-mass term even when there is separation. In a companion paper the flow characteristics for constant acceleration or deceleration are reported.

Lift and Drag Characteristics of an Airfoil and Feedback Flow Control by Flap Actuators in the Low Reynolds Number Region

2015 ◽  
Author(s):  
Toshiki Mori ◽  
Masashi Yamaguchi ◽  
Kyoji Inaoka ◽  
Mamoru Senda
Keyword(s):  
Reynolds Number ◽  
Wind Speed ◽  
Unsteady Flow ◽  
Flow Control ◽  
Flow Condition ◽  
Low Reynolds Number ◽  
High Lift ◽  
Unsteady Flow Condition ◽  
Lift And Drag ◽  
Drag Ratio

The present paper describes the applicability of the flow control device, mini actuators attached on the leading edge of an airfoil, for the flow separation control under unsteady flow condition in the low Reynolds number region. Lift and drag have been measured for a wide variety of the wind speeds (Reynolds numbers) and the angles of attack. Then, effects of simple feedback flow control, where the time-dependent signal of the lift-drag ratio has been used as an input to detect the stall and served as a trigger to start the actuation, have been explored under the unsteady flow condition for evading the stall. For every Reynolds number from 30,000 to 80,000, the actuators worked quite well to delay the stall, increasing both in the lift and the stall angle of attack. Then, threshold value of the lift-drag ratio was determined to detect the stall. Effectiveness of the feedback control of the actuation was demonstrated under the condition of the wind speed decrease which would lead to the stall if no-actuation. Immediately after the velocity decrease, the decrease in the lift-drag ratio below the threshold were detected and the dynamic actuations were started, resulting in evading the stall and keeping high lift. The additional operation of the feedback, stopping the actuation when the lift-drag ratio showed lower than the second threshold, was revealed effective to keep the high lift force under the condition combined with the wind speed increase and decrease.

Air Permeability of Concrete by Thenoz Method

2011 ◽  
Vol 224 ◽  
pp. 132-136 ◽  
Author(s):  
Valdir Moraes Pereira ◽  
Gladis Camarini
Keyword(s):  
Reynolds Number ◽  
Porous Media ◽  
Flow Velocity ◽  
Air Permeability ◽  
Model Tests ◽  
Principal Factor ◽  
Flow Mechanism ◽  
Good Test ◽  
Cement Based Materials

Permeability of cement-based materials is the principal factor that provides its durability. Thus, several methodologies have been developed for measuring this property. Discrepancies in results can be generated due to large number of methods, mathematics equations and methodologies employed. Thenoz method is one method developed for measuring air permeability of porous media and have demonstrated good and satisfactory results, in accordance to several scientific researches. The aim of this work was to study the flow mechanism in a porous media, in particular a concrete media, evaluating Reynolds number and flow velocity of air outflow occurred when Thenoz method was employed to measure concrete air permeability. The Reynolds number results showed that outflow regime occurs in laminar form and validate the hypothesis to confirm the model. Tests were performed to verify the veracity of results obtained in accordance this methodology. Results have shown that air permeability measured by Thenoz method is a good test to evaluate concrete porosity.

Unsteady Analysis of Microvalves With No Moving Parts

2007 ◽  
Vol 23 (1) ◽  
pp. 9-14 ◽  
Author(s):  
C.-T. Wang ◽  
T.-S. Leu ◽  
J.-M. Sun
Keyword(s):  
Unsteady Flow ◽  
Flow Rate ◽  
Reverse Flow ◽  
Volume Flow Rate ◽  
Volume Flow ◽  
Pressure Amplitude ◽  
Flow Conditions ◽  
Unsteady Flow Condition ◽  
The Difference ◽  
Moving Parts

AbstractNo-moving-parts valves (NMPV) pumps produce the net volume flow due to the difference of pressure resistances between forward and reverse flow of a microchannel structure. NMPV has been developed by a number of research groups. However, most of NMPV in these studies are designed and based on steady state flow conditions. Little data is available regarding the NMPV in unsteady flow conditions. In this study, the performances of NMPV under both steady and unsteady flow conditions are investigated numerically. The NMPV used in this study is a diffuser-type microchannel with diffuser angle of 20° because of its outstanding production of net volume flow. By a series of numerical simulations, some useful results would be addressed for the performance of NMPV micropumps. First, Reynolds number confirmed by steady analysis should be greater than 10 (Re > 10) for the NMPV pumps to be more effective. Second, an optimal Strouhal number with maximum net volume flow rate is found at St = 0.013 for the unsteady flow condition. In addition, the relation between the driving pressure amplitude and net volume flow rate with a linear behavior found was helpful to the performance of the micropump system. According to these findings, it was easy for users to operate and design of NMPV micropumps.

The effects of surface roughness and tunnel blockage on the flow past spheres

1974 ◽  
Vol 65 (1) ◽  
pp. 113-125 ◽  
Author(s):  
Elmar Achenbach
Keyword(s):  
Surface Roughness ◽  
Reynolds Number ◽  
Drag Coefficient ◽  
Critical Reynolds Number ◽  
Measurement Techniques ◽  
Flow Conditions ◽  
Number Range ◽  
Flow Past ◽  
Reynolds Number Range ◽  
Shedding Frequency

The effect of surface roughness on the flow past spheres has been investigated over the Reynolds number range 5 × 104 < Re < 6 × 106. The drag coefficient has been determined as a function of the Reynolds number for five surface roughnesses. With increasing roughness parameter the critical Reynolds number decreases. At the same time the transcritical drag coefficient rises, having a maximum value of 0·4.The vortex shedding frequency has been measured under subcritical flow conditions. It was found that the Strouhal number for each of the various roughness conditions was equal to its value for a smooth sphere. Beyond the critical Reynolds number no prevailing shedding frequency could be detected by the measurement techniques employed.The drag coefficient of a sphere under the blockage conditions 0·5 < ds/dt < 0·92 has been determined over the Reynolds number range 3 × 104 < Re < 2 × 106. Increasing blockage causes an increase in both the drag coefficient and the critical Reynolds number. The characteristic quantities were referred to the flow conditions in the smallest cross-section between sphere and tube. In addition the effect of the turbulence level on the flow past a sphere under various blockage conditions was studied.

Computer Simulation of a Drop-Shaped Particle Settling in a Newtonian Fluid

2013 ◽  
Vol 444-445 ◽  
pp. 369-373
Author(s):  
De Ming Nie ◽  
Meng Jiao Zheng
Keyword(s):  
Computer Simulation ◽  
Reynolds Number ◽  
Friction Coefficient ◽  
Drag Coefficient ◽  
Newtonian Fluid ◽  
Particle Shape ◽  
Shape Factor ◽  
Blockage Ratio ◽  
Circular Particle ◽  
Shaped Particle

This work focuses on the effects of the particle shape factor and blockage ratio on the friction coefficient and drag coefficient of the drop-shaped particle for Reynolds number ranging from 10-2 to 102 when the particle is settling under gravity. Comparison with the results of a circular particle has also been presented. It has been shown that the particle friction coefficient keeps constant when Reynolds number is below 1, and increases as Reynolds number increasing when Reynolds number is greater than 1. Furthermore, results have also shown that both the friction coefficient and drag coefficient of the circular particle are smaller than those of the drop-shaped one when Reynolds number is below about 30 while bigger than those of drop-shaped one when Reynolds number is larger than 30.

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