Three-Dimensional Flow Pattern Upstream of a Surface-Mounted Rectangular Obstruction

1989 ◽  
Vol 111 (4) ◽  
pp. 449-456 ◽  
Author(s):  
K. Y. M. Lai ◽  
A. H. Makomaski
Keyword(s):  
Saddle Point ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Computer Code ◽  
Experimental Results ◽  
Circular Cylinders ◽  
Vortex Model ◽  
Flow Phenomena ◽  
The One ◽  
Corner Vortex

A three-dimensional TEACH-like computer code is developed and employed to study the flow phenomena upstream of a rectangular obstruction placed in a two-dimensional turbulent boundary layer. Satisfactory comparison is obtained with the experimental results of Blair (1984, 1987). The general trends, regarding the dependence of vortex dimensions, wall static pressure distributions and saddle point positions on Re = U∞δ*/ν and on D* = D/δ*, are similar to the experimental results for circular cylinders (Eckerle and Langston, 1986 and Baker, 1980). The position of the saddle point depends on the turbulence intensity in the primary vortex. The pressure coefficient at the foot of the obstruction depends solely on D* if no corner vortex exists. This coefficient is reduced when a corner vortex is present. All the computed flow patterns are similar to the one-vortex model of Eckerle and Langston (1986). The four-vortex model reported by Baker (1980) and Hunt et al. (1978) cannot be found in any of the calculations.

Numerical investigation of the propagation of shock waves in rigid porous materials: development of the computer code and comparison with experimental results

1996 ◽  
Vol 324 ◽  
pp. 163-179 ◽  
Author(s):  
A. Levy ◽  
G. Ben-Dor ◽  
S. Sorek
Keyword(s):  
Porous Materials ◽  
Initial Conditions ◽  
Computer Code ◽  
Experimental Results ◽  
Numerical Code ◽  
Materials Development ◽  
Numerical Predictions ◽  
Wide Range ◽  
Dimensional Version ◽  
The One

The governing equations of the flow field which is obtained when a thermoelastic rigid porous medium is struck head-one by a shock wave are developed using the multiphase approach. The one-dimensional version of these equations is solved numerically using a TVD-based numerical code. The numerical predictions are compared to experimental results and good to excellent agreements are obtained for different porous materials and a wide range of initial conditions.

Modeling Hydroplaning and Effects of Pavement Microtexture

2005 ◽  
Vol 1905 (1) ◽  
pp. 166-176 ◽  
Author(s):  
G. P. Ong ◽  
T. F. Fwa ◽  
J. Guo
Keyword(s):  
Three Dimensional ◽  
Flow Simulation ◽  
Experimental Results ◽  
Tire Pressure ◽  
Finite Volume Model ◽  
Proposed Model ◽  
Loss Of Contact ◽  
The One ◽  
Theoretical Considerations ◽  
Good Agreement

Hydroplaning on wet pavement occurs when a vehicle reaches a critical speed and causes a loss of contact between its tires and the pavement surface. This paper presents the development of a three-dimensional finite volume model that simulates the hydroplaning phenomenon. The theoretical considerations of the flow simulation model are described. The simulation results are in good agreement with the experimental results in the literature and with those obtained by the well-known hydroplaning equation of the National Aeronautics and Space Administration (NASA). The tire pressure–hydroplaning speed relationship predicted by the model is found to match well the one obtained with the NASA hydroplaning equation. Analyses of the results of the present study indicate that pavement microtexture in the 0.2- to 0.5-mm range can delay hydroplaning (i.e., raise the speed at which hydroplaning occurs). The paper also shows that the NASA hydroplaning equation provides a conservative estimate of the hydroplaning speed. The analyses in the present study indicate that when the microtexture of the pavement is considered, the hydroplaning speed predicted by the proposed model deviates from the speed predicted by the smooth surface relationship represented by the NASA hydroplaning equation. The discrepancies in hydroplaning speed are about 1% for a 0.1-mm microtexture depth and 22% for a 0.5-mm microtexture depth. The validity of the proposed model was verified by a check of the computed friction coefficient against the experimental results reported in the literature for pavement surfaces with known microtexture depths.

scholarly journals Hydrodynamic Analysis of 3D Hydrofoil Using Nonuniform Rational B-Spline and Boundary Element Method

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Moloud ArianMaram ◽  
Mahmoud Ghiasi ◽  
Hassan Ghassemi ◽  
Hamid Reza Ghafari
Keyword(s):  
Boundary Element Method ◽  
Boundary Element ◽  
Basic Equation ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Computer Code ◽  
Hydrodynamic Analysis ◽  
B Spline ◽  
Coefficient Distribution ◽  
Element Method

In this paper, two different 3D hydrofoils with profiles NACA0012 are simulated in the potential flow. Boundary element method (BEM) and nonuniform rational B-spline (NURBS) are coupled to reduce error and increase accuracy. The computer code is developed in different submergence depths (d), flow velocities (U), and various angles of attack (AoA), and the pressure is obtained by NURBS formulation. The pressure on a 3D hydrofoil with NACA412 profile iscompared with other existing methods. The validity of result is revealed. The accuracy of the results is acceptable. The competition of the two models’ results indicates that the increasing chord length leads to increase in C p min , and the decrease in depth and angle of attack leads to the growing value of C p min . Moreover, when the flow velocity is changed, the changes of potential and pressure coefficient distribution do not follow the specific trend. NURBS is a basic equation in different CAD packages because it is able to mesh surfaces. This study demonstrates that this algorithm does mesh surface of high quality, so it can be developed to generate mesh on the submerged three-dimensional bodies .

scholarly journals Behavior of Three-Dimensional Boundary Layers in a Radial Inflow Turbine Scroll

1993 ◽  
Author(s):  
Kazuo Hara ◽  
Masato Furukawa ◽  
Masahiro Inoue
Keyword(s):  
Boundary Layer ◽  
Secondary Flow ◽  
Three Dimensional ◽  
Radial Pressure ◽  
Inlet Region ◽  
Flow Phenomena ◽  
Dimensional Boundary ◽  
Radial Inflow Turbine ◽  
The One ◽  
Circumferential Nonuniformity

A detailed experimental investigation was carried out to examine the three-dimensional boundary layer characteristics in a radial inflow turbine scroll. Some basic flow phenomena and growth of secondary flow were also investigated. In the inlet region of the scroll, the incoming boundary layer begins to have the skewed nature, namely the radially inward secondary flow caused by the radial pressure gradient. From the inlet region to the one third of the scroll circumference, the secondary flow grows so strongly that the most of the low momentum fluid in the incoming boundary layer are transported to the nozzle region. The succeeding elimination of the low momentum fluid in the boundary layer suppresses growth of the boundary layer further downstream, where the boundary layer shows a similarity of velocity profile. The distributions of the boundary layer properties in the scroll correspond well to those of the flow properties at the nozzle. The behavior of the boundary layer in the scroll is found to affect the circumferential nonuniformity of the nozzle flow field.

scholarly journals Experimental and Numerical Investigation of Tip Leakage Flows in a Roots Blower

Designs ◽  
2020 ◽  
Vol 4 (1) ◽  
pp. 3
Author(s):  
Shuaihui Sun ◽  
Gursharanjit Singh ◽  
Ahmed Kovacevic ◽  
Christoph Bruecker
Keyword(s):  
Three Dimensional ◽  
Operating Conditions ◽  
Experimental Results ◽  
Leakage Flow ◽  
Leakage Flows ◽  
Positive Displacement ◽  
Velocity Magnitude ◽  
Compressor Rotor ◽  
Gap Flow ◽  
Flow Phenomena

Computational fluid dynamics (CFD) can help in understanding the nature of leakage flow phenomena inside the rotary positive displacement machines (PDMs). However, due to the lack of experimental results, the analysis of leakage flows in rotary PDMs by CFD has not yet been fully validated. Particle image velocimetry (PIV) tests with a microscopic lens and phase-lock were conducted to obtain the velocity field around the tip gap in an optical Roots blower. The three-dimensional unsteady CFD model of the Roots blower with the dynamic grids generated by Screw Compressor Rotor Grid Generation (SCORG) was established to predict the gap flow under the same operating conditions. The images obtained by the PIV tests were analyzed and some factors which compromise the quality of test results in the gap flow were identified, such as reflections and transparency of the window. The flow fields obtained by CFD have the same flow pattern and velocity magnitude as the experimental results in the majority of observed regions but overestimate the leakage flow velocity. The CFD results show a vortex induced by the leakage flow in the downstream region of the gap. The flow losses in the tip gap mainly happen at the entrance upstream of the gap. Finally, some suggestions for future work are discussed.

Brief Reviews of Some Time-Dependent Flows

1992 ◽  
Vol 114 (3) ◽  
pp. 283-298 ◽  
Author(s):  
T. Sarpkaya
Keyword(s):  
Three Dimensional ◽  
Separated Flows ◽  
Time Dependent ◽  
Circular Cylinders ◽  
Vortical Structures ◽  
Unsteady Separation ◽  
Flow Phenomena ◽  
Fundamental Research ◽  
The Subject ◽  
New Research

Separated flows in general and time-dependent flows in particular provide fertile territory for fundamental research in fluid dynamics and account for much of the subject matter. Thus, it is thought appropriate to review some of these unsteady flows with special emphasis on hydrodynamic applications which are, admittedly, of special interest to this writer: unsteady separation; characteristics of impulsively and nonimpulsively-started flow about cylinders; excursion of separation points on circular cylinders in oscillating flow; separation and other flow phenomena governing the unsteady maneuvers of large submerged bodies, and, finally, the three-dimensional footprints of subsurface vortical structures rising toward the free surface. It is hoped that these concise reviews will enhance communication between various groups of researchers, draw attention to many exciting phenomena in naval hydrodynamics, and inspire new research topics.

Performance of Inward Radial Flow Turbines under Steady Flow Conditions with Special Reference to High Pressure Ratios and Partial Admission

1969 ◽  
Vol 184 (1) ◽  
pp. 1027-1042 ◽  
Author(s):  
F. J. Wallace ◽  
P. R. Cave ◽  
J. Miles
Keyword(s):  
High Speed ◽  
Radial Flow ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Design Tool ◽  
Experimental Results ◽  
Performance Measurements ◽  
One Dimensional ◽  
Partial Admission ◽  
The One

The paper describes an extension of an earlier and very successful one-dimensional analysis by one of the authors (reference (1)) for design and off-design performance evaluation of inward radial flow turbines to include four cases not covered by the earlier analysis: high overall pressure ratios leading to either nozzle or rotor choking; partial admission; variable nozzle angle; allowance for nozzle and rotor loss coefficients (references (2) and (3)). Each of these extensions of the original theory has been programmed in FORTRAN. The full admission results are compared with performance measurements obtained on a C.A.V. type 01 turbine in conjunction with a specially designed high-speed dynamometer for pressure ratios up to 1.6, the analysis being extended to a maximum value of 4.0. The partial admission results are compared with experimental results reported in reference (4). The variable nozzle angle results are given as an example of the flexibility of the method. Finally, the loss coefficient treatment of Benson (reference (2)) which was based on reference (1) in conjunction with experimental results reported in reference (5), is applied to the full admission tests of the present paper. The object of the paper is to give a comprehensive account of the power of the one-dimensional treatment as a design tool, with the inference that two-and three-dimensional treatments (references (6)-(9)) are basically more suitable for detailed flow analysis rather than basic design.

Calculations of average characteristics of EAS components and Monte Carlo calculations of their fluctuations using different models of nuclear interactions. I. Methodology—Lateral structure and transition curve of electrons

1968 ◽  
Vol 46 (10) ◽  
pp. S147-S152 ◽  
Author(s):  
G. T. Murthy ◽  
K. Sivaprasad ◽  
M. V. Srinivasa Rao ◽  
S. C. Tonwar ◽  
R. H. Vatcha ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Three Dimensional ◽  
High Energy ◽  
Primary Energy ◽  
Experimental Results ◽  
Transition Curve ◽  
Average Value ◽  
Shower Maximum ◽  
The One ◽  
Lateral Structure

Properties of extensive air showers are computed by two methods based on eight plausible models of ultra-high-energy interactions of nucleons and pions with air nuclei. The first method is the numerical solution of the diffusion equations describing the one-dimensional nuclear cascade, from which the average properties of nucleon-initiated showers of given energy are deduced. The second method is Monte Carlo simulation of the three-dimensional nuclear cascades from a sample of which typical shower properties and the extent of their fluctuations are estimated.1. For showers of size < 106, the deduced shower absorption lengths are consistent with experimental results only for models involving nucleon pair production.2. The accuracy of experimental results on the depth of the shower maximum at different primary energies (105–1010 GeV) available at present is insufficient to select any particular model.3. Monte Carlo size distributions for a given primary energy indicate that with the primary energy spectrum known at present, showers of a given size originate from primaries of a relatively narrow range.4. The electron lateral structure parameter, α, fluctuates considerably for showers of primary energy < 106 GeV; the spread decreases with the primary energy.5. The average value of α increases with primary energy up to 106 GeV and saturates at ~ 1.2 for showers of larger sizes.

An experimental and numerical study of the flow past elliptic cylinder arrays

2001 ◽  
Vol 215 (11) ◽  
pp. 1287-1301 ◽  
Author(s):  
D Castiglia ◽  
S Balabani ◽  
G Papadakis ◽  
M Yianneskis
Keyword(s):  
Numerical Study ◽  
Three Dimensional ◽  
Elliptic Cylinder ◽  
Experimental Results ◽  
Circular Cylinders ◽  
Axis Ratio ◽  
Eddy Simulation ◽  
Cylinder Arrays ◽  
Numerical Predictions ◽  
Flow Past

The subcritical flow over an array of elliptic cylinders with an axis ratio of 1:2 was studied both experimentally and numerically. The mean velocities, turbulence levels and the vortex dynamics of the array were determined experimentally by flow visualization and using a laser Doppler anemometer (LDA) and the flow was modelled using three-dimensional large eddy simulation (LES). The experimental results were compared with results obtained previously using circular cylinders and with numerical predictions of the flow. The study indicated that the flow past such a widely spaced array is characterized by low turbulence levels and poor lateral mixing compared with conventional circular cylinder arrays, and a weak flow periodicity with a constant Strouhal number of 0.11 was detected in downstream rows. The predicted mean and r.m.s. velocities, as well as the flow periodicity, were in good agreement with the experimental results.

scholarly journals Numerical Investigation of Internal Solitary Wave Forces on Submarines in Continuously Stratified Fluids

2021 ◽  
Vol 9 (12) ◽  
pp. 1374
Author(s):  
Jingyuan Li ◽  
Qinghe Zhang ◽  
Tongqing Chen
Keyword(s):  
Nonlinear Models ◽  
Pressure Coefficient ◽  
Three Dimensional ◽  
Variable Density ◽  
Experimental Results ◽  
Navier Stokes ◽  
Wave Forces ◽  
Stratified Fluids ◽  
Navier Stokes Equation ◽  
Initial Field

A numerical model of internal solitary waves in continuously stratified fluids is developed by introducing a density transport equation to the three-dimensional Navier–Stokes equation and adopting the fully nonlinear models of the Dubreil-Jacotin-Long equation to obtain the initial field of the ISW. The corresponding turbulence model has also been modified to ensure that it considers the variable density field. Comparisons between numerical simulation results and experimental results show that the total resistance, the nondimensional pressure coefficient, and the nondimensional friction coefficient for the standard submarine model proposed by the Defense Advanced Research Projects Agency under different flow field conditions are highly consistent with the experimental results. The model established is used to numerically analyse the forces and moments of the standard submarine model encountering ISWs at different submergence depths. The influence of the rotation centre position on the moment is discussed, and the position range of the optimal rotation centre is proposed.

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