The Decay of Highly Skewed Flows in Ducts

1975 ◽  
Vol 97 (1) ◽  
pp. 85-92 ◽  
Author(s):  
B. Quinn
Keyword(s):  
Velocity Profile ◽  
Pressure Coefficient ◽  
Point Of View ◽  
Local Pressure ◽  
Friction Forces ◽  
Arbitrary Section

The development of a very nonuniform or skewed velocity profile in passing through a diffuser has been examined from the point of view of velocity components induced by line vortices. Account is taken of the effect of dissipation and straining on the strengths of the vortices and the intensities of the induced velocities. Changes with the integrated momentum of the perturbation velocities contribute to the local pressure in the duct, or diffuser, along with friction forces and area changes. An expression is derived for the pressure coefficient of a highly skewed profile flowing through a duct of arbitrary section. The results of experiments with an ejector apparatus are presented and found to support the analytical conclusions. In contrast with slightly skewed flows, diffusion will not inhibit the decay of highly skewed profiles.

Partially Cavitating Hydrofoils: Experimental and Numerical Analysis*

2000 ◽  
Vol 44 (01) ◽  
pp. 40-58
Author(s):  
Christian Pellone ◽  
Thierry Maître ◽  
Laurence Briançon-Marjollet
Keyword(s):  
Numerical Models ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Navier Stokes ◽  
Viscous Effects ◽  
Local Pressure ◽  
Two Phase ◽  
Complete Study ◽  
Flow Configurations ◽  
Potential Methods

The numerical modeling of partially cavitating foils under a confined flow configuration is described. A complete study of previous numerical models highlights that the presence of a turbulent and two-phase wake, at the rear of the cavity, has a nonnegligible effect on the local pressure coefficient, the cavitation number, the cavity length and the lift coefficient; hence viscous effects must be included. Two potential methods are used, each being coupled with a calculation of the boundary layer developed downstream of the cavity. So, an "open cavity" numerical model, as it is called, was developed and tested with two types of foil: a NACA classic foil and a foil of which the profile is obtained performing an inverse calculation on a propeller blade test section. On the other hand, under noncavitating conditions, for each method, the results are compared with the results obtained by the Navier-Stokes solver "FLUENT." The cavitating flow configurations presented herein were carried out using the small hydrodynamic tunnel at Bassin d'Essais des Carènes [Val de Reuil, France]. The results obtained by the two methods are compared with experimental measurements.

Influence of a Finite Width Micro-Tab on the Spanwise Lift Distribution

2013 ◽  
Author(s):  
D. Holst ◽  
A. B. Bach ◽  
C. N. Nayeri ◽  
C. O. Paschereit
Keyword(s):  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Global Changes ◽  
Finite Width ◽  
Local Pressure ◽  
Low Reynolds Numbers ◽  
Pressure Distributions ◽  
Coefficient Distribution ◽  
Stereo Particle Image Velocimetry ◽  
The Impact

The results of surface pressure measurements are presented in this paper to gain further insight into the lift changing influence of finite width micro-tabs, especially in adjacent airfoil sections. Micro-tabs are a promising concept for load control on wind turbines. Local pressure distributions were measured in several rows of pressure taps in the vicinity of the finite width micro-tab attached to a FX 63-137 profile at low Reynolds numbers. The investigation focuses on length dependency, chordwise position, and interaction between two micro-tabs. Additionally, stereo Particle-Image-Velocimetry measurements were conducted to study the structure, sense of rotation, and influence of tab-induced tip vortices, as well as the impact of a finite width micro-tab on the model’s near wake. Experiments reveal relative changes of more than 30 % in the pressure coefficient distribution upstream of several micro-tab configurations. Furthermore, increments of 20 % are recorded in neighbouring sections not directly controlled by micro-tabs. Even higher changes are obtained in the region between two tabs. These improvements are attained due to local and global changes in the effective camber.

LES Study of the Influence of a Train-Nose Shape on the Flow Structures Under Cross-Wind Conditions

2008 ◽  
Vol 130 (9) ◽  
Author(s):  
Hassan Hemida ◽  
Siniša Krajnović
Keyword(s):  
High Speed ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Flow Patterns ◽  
Surface Flow ◽  
Flow Structures ◽  
Local Pressure ◽  
Freestream Velocity ◽  
Train Simulation ◽  
Long Nose

Cross-wind flows around two simplified high-speed trains with different nose shapes are studied using large-eddy simulation (LES) with the standard Smagorinsky model. The Reynolds number is 3×105 based on the height of the train and the freestream velocity. The cross section and the length of the two train models are identical while one model has a nose length twice that of the other. The three-dimensional effects of the nose on the flow structures in the wake and on the aerodynamic quantities such as lift and side force coefficients, flow patterns, local pressure coefficient, and wake frequencies are investigated. The short-nose train simulation shows highly unsteady and three-dimensional flow around the nose yielding more vortex structures in the wake. These structures result in a surface flow that differs from that in the long-nose train flow. They also influence the dominating frequencies that arise due to the shear-layer instabilities. Prediction of vortex shedding, flow patterns in the train surface, and time-averaged pressure distribution obtained from the long-nose train simulation are in good agreement with the available experimental data.

scholarly journals Briquetting of structurally inhomogeneous porous materials

2020 ◽  
Vol 65 (2) ◽  
pp. 205-214
Author(s):  
O. M. Dyakonov
Keyword(s):  
Porous Body ◽  
Pressure Coefficient ◽  
Energy Condition ◽  
Contact Friction ◽  
Equilibrium Equations ◽  
Friction Forces ◽  
Pressing Process ◽  
Deformation Work ◽  
Pressure Stress ◽  
Force Calculation

The work is devoted to solving the axisymmetric problem of the theory of pressing porous bodies with practical application in the form of force calculation of metallurgical processes of briquetting small fractional bulk materials: powder, chip, granulated and other metalworking wastes. For such materials, the shape of the particles (structural elements) is not geometrically correct or generally definable. This was the basis for the decision to be based on the continual model of a porous body. As a result of bringing this model to a two-dimensional spatial model, a closed analytical solution was obtained by the method of jointly solving differential equilibrium equations and the Guber–Mises energy condition of plasticity. The following assumptions were adopted as working hypotheses: the normal radial stress is equal to the tangential one, the lateral pressure coefficient is equal to the relative density of the compact. Due to the fact that the problem is solved in a general form and in a general formulation, the solution itself should be considered as methodological for any axisymmetric loading scheme. The transcendental equations of the deformation compaction of a porous body are obtained both for an ideal pressing process and taking into account contact friction forces. As a result of the development of a method for solving these equations, the formulas for calculating the local characteristics of the stressed state of the pressing, as well as the integral parameters of the pressing process are derived: pressure, stress, and deformation work.

Turbulent Flow in the Entry Region of a Rough Pipe

1974 ◽  
Vol 96 (1) ◽  
pp. 62-68 ◽  
Author(s):  
Jeng-Song Wang ◽  
J. P. Tullis
Keyword(s):  
Boundary Layer ◽  
Mathematical Model ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Velocity Profile ◽  
Turbulent Flow ◽  
Boundary Layer Thickness ◽  
Static Pressure ◽  
Pressure Coefficient ◽  
Reynolds Numbers

The general characteristics of mean turbulent flow in the entry region of a rough pipe are discussed. A mathematical model is presented for predicting the development of boundary layer thickness, core velocity, and pressure coefficient. Measurements were made of static pressure and velocity profiles in a 12-in. dia pipe at Reynolds numbers between 7 × 105 and 3.7 × 106. Water was used as the fluid. Data are included on the length required for the wall shear stress to become constant, for the boundary layer to reach the pipe centerline and for the velocity profile to become fully developed.

Direct measurements of skin friction in a turbulent boundary layer with a strong adverse pressure gradient

1980 ◽  
Vol 101 (1) ◽  
pp. 79-95 ◽  
Author(s):  
D. Frei ◽  
H. Thomann
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Skin Friction ◽  
Circular Cross Section ◽  
Adverse Pressure Gradient ◽  
Small Element ◽  
Pressure Gradients ◽  
Local Pressure ◽  
Friction Forces

This paper describes a new balance, suitable for direct measurement of skin friction in turbulent boundary layers with severe pressure gradients. The gaps between the floating element and the surrounding wall are filled with a liquid in order to eliminate disturbing pressure forces on the element. The resulting friction forces are measured with piezo-electric transducers with high sensitivity and extremely small element displacement.Skin friction measurements were taken in the turbulent boundary layer of a wind tunnel with circular cross-section at M [les ] 0·25. Severe adverse pressure gradients were generated by means of a step on the wall or, alternatively, by a conical centre body.The new apparatus was mainly used to investigate the error of Preston tubes in adverse pressure gradients. It was necessary to develop a new measuring technique to improve the repeatability of the Preston tube readings.The Preston tube error was found to depend on both the local pressure gradient P = (dp/dx) ν/ρ3τ and on the Preston tube diameter uτd/ν and to be independent of the upstream pressure distribution for the range of parameters covered by the experiments.

scholarly journals Experimental determination of wind action on triangular solar panel assemblies

2020 ◽  
Vol 313 ◽  
pp. 00050
Author(s):  
Olga Hubova ◽  
Michal Franek ◽  
Marek Macak
Keyword(s):  
Wind Tunnel ◽  
Pressure Coefficient ◽  
Wind Load ◽  
Solar Panel ◽  
Maximum Pressure ◽  
Experimental Measurements ◽  
Local Pressure ◽  
Net Pressure ◽  
Conservative Values

The article deals with aerodynamic study of solar panel assemblies. Experimental measurements were realized in BLWT wind tunnel. The aim of the solution was to determine the maximum pressure and suction wind load on top and bottom surfaces of panels. The resulting net pressure coefficient represents the maximum local pressure in each panel row as maximum values from all wind directions. The experimentally obtained cp,net values were compared with the conservative values in EN 1991-1-4 for open monopitch canopies. A lower wind load in the inner regions of the triangular assemblies should be used in the design of fixing supports.

scholarly journals Force calculation of the process of briquetting powder, chip and other bulk materials

2019 ◽  
pp. 118-125
Author(s):  
O. M. Dyakonov
Keyword(s):  
Porous Body ◽  
Pressure Coefficient ◽  
Energy Condition ◽  
Contact Friction ◽  
Equilibrium Equations ◽  
Bulk Materials ◽  
Friction Forces ◽  
Pressing Process ◽  
Deformation Work ◽  
Force Calculation

The work is devoted to solving the axisymmetric problem of the theory of pressing porous bodies with practical application in the form of force calculation of metallurgical processes of briquetting small fractional bulk materials: powder, chip, granulated and other metalworking wastes. For such materials, the shape of the particles (structural elements) is not geometrically correct or generally definable. This was the basis for the decision to be based on the continual model of a porous body. As a result of bringing this model to a two-dimensional spatial model, a closed analytical solution was obtained by the method of jointly solving differential equilibrium equations and the Guber-Mises energy condition of plasticity. The following assumptions were adopted as working hypotheses: the radial shear stress is equal to the tangential one, the lateral pressure coefficient is equal to the relative density of the compact. Due to the fact that the problem is solved in a general form and in a general formulation, the solution itself should be considered as methodological for any axisymmetric loading scheme. The transcendental equations of the deformation compaction of a porous body are obtained both for an ideal pressing process and taking into account contact friction forces. As a result of the development of a method for solving these equations, the formulas for calculating the local characteristics of the stressed state of the pressing, as well as the integral parameters of the pressing process are derived: pressure, stress, and deformation work.

scholarly journals Numerical and experimental determination of wind load on photovoltaic panel assemblies

2020 ◽  
Vol 63 (4) ◽  
pp. 49-63
Author(s):  
Oľga Hubová ◽  
Michal Franek ◽  
Marek Macák
Keyword(s):  
Computer Simulation ◽  
Pressure Coefficient ◽  
Wind Load ◽  
Maximum Pressure ◽  
Wind Flow ◽  
Experimental Measurements ◽  
Local Pressure ◽  
Photovoltaic Panel ◽  
Net Pressure

The article presents the aerodynamic study of solar panel assemblies and determination of wind load. In the first part, the task is solved by computer simulation of the wind flow around the proposed rectangular assembly in the scale of 1:1 using the FLUENT ANSYS program; realization of experimental measurements in the wind tunnel with a boundary layer (BLWT) in Bratislava is presented subsequently. The aim of the solution was to determine the maximum pressure and suction wind load on top and bottom surfaces of panels. The resulting net pressure coefficient represents the maximum local pressure in each panel row as maximum values from all wind directions. The experimentally obtained net pressure coefficient values were compared with computer simulation and the procedures mentioned in standard STN EN 1991-1-4. It can be seen that the inner panels are loaded considerably less than the standard defines. The panels placed on the side of the assembly or on the edge of the aisle are loaded significantly more than the standard defines. Frontal panels are also less wind stressed than in the standard defines.

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