Optimized Laminar Axisymmetrical Nozzle Design Using a Numerically Validated Thwaites Method

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
Philippe Versailles ◽  
Jeffrey M. Bergthorson
Keyword(s):  
Design Tool ◽  
Pressure Gradients ◽  
Efficient Design ◽  
Internal Flows ◽  
Cfd Simulations ◽  
Integral Boundary ◽  
Design And Optimization ◽  
Computational Fluid Dynamics Cfd ◽  
Historical Developments ◽  
Good Agreement

This paper presents the Thwaites method as an accurate and efficient design tool for laminar, axisymmetrical nozzles. Based on historical developments, it is improved to describe internal flows with highly favorable pressure gradients in cylindrical coordinates. The calculation of the core flow velocity distribution based on the continuity equation is proposed as a replacement to other sophisticated numerical methods. A remarkably good agreement is obtained when comparing the results of the current Thwaites method against those of computational fluid dynamics (CFD) simulations, for which the integral boundary layer thicknesses are calculated with equations developed from first principles in the course of the work. This consistency among the results and the low time and resource costs of the Thwaites method confirm its applicability and usefulness as an engineering design and optimization tool.

Vortex-Induced Vibration of a Three-Body Launch Vehicle During Ascent

2002 ◽  
Author(s):  
Kirk W. Dotson ◽  
William A. Engblom
Keyword(s):  
Vortex Pair ◽  
Launch Vehicles ◽  
Cfd Simulations ◽  
Structural Dynamic ◽  
Structural Responses ◽  
Wind Tunnel Data ◽  
Computational Fluid Dynamics Cfd ◽  
Test Instrumentation ◽  
Three Body ◽  
Good Agreement

Launch vehicles composed of three bodies can experience the shedding of vortices due to strong crossflow acceleration towards the center body, or core. Upon formation, the vortices obstruct the freestream flow, which diverts the local angle of attack towards the opposite side of the core, and a new pair of vortices are formed. This alternate vortex-pair shedding can induce significant pitch structural responses during transonic flight. Computational fluid dynamics (CFD) simulations have been used to illustrate the phenomenon and to generate forcing functions for structural dynamic analyses. Structural responses from these analyses are in good agreement with flight responses. This success suggests that CFD can be used for preflight predictions of the phenomenon. It also indicates that CFD can be used to supplement wind tunnel data when the test instrumentation does not adequately resolve the alternate vortex-pair shedding.

Design of Curved Annular Diffusers

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Vinayender Kuchana ◽  
N. Balakrishnan ◽  
Balamurugan Srinivasan
Keyword(s):  
Design Space ◽  
Pressure Gradients ◽  
Cfd Simulations ◽  
Maximum Slope ◽  
Pressure Fields ◽  
Annular Diffuser ◽  
Computational Fluid Dynamics Cfd ◽  
Curvature Distribution ◽  
Automated Optimization ◽  
End Wall

Abstract Influence of curvature distribution and area-ratio (AR) distribution on the pressure fields within the curved annular diffuser are discussed. General guidelines for end-wall contouring to control the pressure gradients on the diffuser walls are evolved and further demonstrated through computational fluid dynamics (CFD) simulations. Also, detailed guidelines for controlling the adverse pressure gradients (APG) on duct walls are presented. A geometry generation methodology (GGM) which enables both design and evaluation of curved annular diffusers based on the guidelines evolved is presented. The approach presented deals with the sensitivity of the duct performance parameters to duct wall modifications. In that sense, the work per se is not a description of an automated optimization process, but rather about the physical principles that can guide such an optimization. An aggressive diffuser design space is identified with ducts of maximum slope of 50 deg and maximum divergence angle between the outer and inner walls of 10 deg for length to inlet height ratio ranging from 1.25 to 2.5. Part of the identified design space for which the flow separation can be eliminated based on the guidelines evolved is demarcated. The need for flow control, possibly passive, is established for more aggressive designs.

Extent, capacity and possibilities of computational fluid dynamics as a design tool for pump intakes: a review

2018 ◽  
Vol 18 (5) ◽  
pp. 1518-1530 ◽  
Author(s):  
Jie Zhang ◽  
Tien Yee
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Three Dimensional ◽  
Design Tool ◽  
Cfd Modeling ◽  
Cfd Simulations ◽  
Pump Station ◽  
Computational Fluid Dynamics Cfd ◽  
Future Direction ◽  
Computational Resources

Abstract Flow near pump intakes is three-dimensional in nature, and is affected by many factors such as the geometry of the intake bay, uniformity of approach flow, critical submergence, placements and operation combinations of pumps and so on. In the last three decades, advancement of numerical techniques coupled with the increase in computational resources made it possible to conduct computational fluid dynamics (CFD) simulations on pump intakes. This article reviews different aspects involved in CFD modeling of pump station intakes, outlines the challenges faced by current CFD modelers, and provides an attempt to forecast future direction of CFD modeling of pump intakes.

Method for Quick Prediction of Windage Power Loss

2014 ◽  
Author(s):  
Qide Zhang ◽  
Kannan Sundaravadivelu ◽  
Ningyu Liu ◽  
Quan Jiang
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Empirical Formula ◽  
Power Loss ◽  
Hard Disk Drives ◽  
Measurement Data ◽  
Disk Drives ◽  
Cfd Simulations ◽  
Computational Fluid Dynamics Cfd ◽  
Good Agreement

This work introduces a method by using an empirical formula to quickly predict windage caused power loss of hard disk drives. The results obtained by the empirical formula are compared with those obtained by computational fluid dynamics (CFD) simulations and validated by the experimental measurement data. Good agreement is observed among these three sets of data.

Influence of Jordanian zeolite on the performance of a solar still: experiments and CFD simulation studies

2016 ◽  
Vol 16 (6) ◽  
pp. 1700-1709 ◽  
Author(s):  
Yazan Taamneh
Keyword(s):  
Experimental Data ◽  
Phase Change ◽  
Cfd Simulation ◽  
Volume Fraction ◽  
Solar Still ◽  
Cfd Simulations ◽  
Two Phase ◽  
Vof Model ◽  
Computational Fluid Dynamics Cfd ◽  
Good Agreement

Computational fluid dynamics (CFD) simulations were performed for experiments carried out with two identical pyramid-shaped solar stills. One was filled with Jordanian zeolite-seawater and the second was filled with seawater only. This work is focused on CFD analysis validation with experimental data conducted using a model of phase change interaction (evaporation-condensation model) inside the solar still. A volume-of-fluid (VOF) model was used to simulate the inter phase change through evaporation-condensation between zeolite-water and water vapor inside the two solar stills. The effect of the volume fraction of the zeolite particles (0 ≤ ϕ ≤ 0.05) on the heat and distillate yield inside the solar still was investigated. Based on the CFD simulation results, the hourly quantity of freshwater showed a good agreement with the corresponding experimental data. The present study has established the utility of using the VOF two phase flow model to provide a reasonable solution to the complicated inter phase mass transfer in a solar still.

Active Air Flow Control to Reduce Cavity Receiver Heat Loss

2015 ◽  
Author(s):  
J. Jack Zhang ◽  
John D. Pye ◽  
Graham O. Hughes
Keyword(s):  
Heat Loss ◽  
Thermal Power ◽  
Solar Thermal ◽  
Cfd Simulations ◽  
Air Curtain ◽  
Fluid Physics ◽  
Computational Fluid Dynamics Cfd ◽  
Optimum Velocity ◽  
Solar Receiver ◽  
Good Agreement

Convective air flows are a significant source of thermal loss from tubular cavity receivers in concentrating solar-thermal power (CSP) applications. Reduction in these losses is traditionally achieved by tailoring the cavity geometry, but the potential of this method is limited by the aperture size. The use of active airflow control, in the form of an air curtain, is an established practice to prevent infiltration of cold air through building doorways. Its application in reducing solar receiver convective heat loss is new. In this study, computational fluid dynamics (CFD) simulations are presented for the zero wind case, demonstrating that an optimised air curtain can readily reduce convective losses by more than 45%. A parametric investigation of jet direction and speed indicates that two distinct optimal air curtain flow structures exist. In the first, the jet reduces the size of the convective zone within the cavity by partially sealing the aperture. The optimum velocity range for this case occurs with a low strength jet. At higher jet speeds, the losses are generally set by the flow induced in the cavity and entrainment into the jet. However, a second optimal configuration is discovered for a narrow range of jet parameters, where the entrainment is reduced due to a shift in the stack neutral pressure level, allowing the jet to fully seal the cavity. A physical model is developed, based on the fluid physics of a jet and the ‘deflection modulus’ concept typically used to characterise air curtains in building heating and ventilation applications. The model has been applied to the solar thermal cavity case, and shows good agreement with the computational results.

Heat Transfer of Springs in Oblique Crossflows

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Daniel B. Biggs ◽  
Christopher B. Churchill ◽  
John A. Shaw
Keyword(s):  
Heat Transfer ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Experimental Program ◽  
Convection Heat ◽  
Computational Tool ◽  
Cfd Simulations ◽  
Nonmonotonic Dependence ◽  
Computational Fluid Dynamics Cfd ◽  
Good Agreement

An experimental program is presented of heated tension springs in an external crossflow over a range of laminar Reynolds numbers, spring stretch ratios, and angles of attack. Extensive measurements of the forced convection heat transfer of helical wire within a wind tunnel reveal an interesting nonmonotonic dependence on angle of attack. Computational fluid dynamics (CFD) simulations, showing good agreement with the experimental data, are used to explore the behavior and gain a better understanding of the observed trends. A dimensionless correlation is developed that well captures the experimental and CFD data and can be used as an efficient computational tool in broader applications.

scholarly journals Investigating the Effect of Heterogeneous Hull Roughness on Ship Resistance Using CFD

2021 ◽  
Vol 9 (2) ◽  
pp. 202
Author(s):  
Soonseok Song ◽  
Yigit Kemal Demirel ◽  
Claire De Marco Muscat-Fenech ◽  
Tonio Sant ◽  
Diego Villa ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Reynolds Number ◽  
Shear Stress ◽  
Flow Characteristics ◽  
Cfd Simulations ◽  
Ship Resistance ◽  
Wigley Hull ◽  
Computational Fluid Dynamics Cfd ◽  
Good Agreement

Research into the effects of hull roughness on ship resistance and propulsion is well established, however, the effect of heterogeneous hull roughness is not yet fully understood. In this study, Computational Fluid Dynamics (CFD) simulations were conducted to investigate the effect of heterogeneous hull roughness on ship resistance. The Wigley hull was modelled with various hull conditions, including homogeneous and heterogeneous hull conditions. The results were compared against existing experimental data and showed a good agreement, suggesting that the CFD approach is valid for predicting the effect of heterogeneous hull roughness on ship resistance. Furthermore, the local distributions of the wall shear stress and roughness Reynolds number on the hull surface were examined to assess the flow characteristics over the heterogeneous hull roughness.

scholarly journals Rapid Prototyping of Inertial MEMS Devices through Structural Optimization

Sensors ◽  
2021 ◽  
Vol 21 (15) ◽  
pp. 5064
Author(s):  
Daniele Giannini ◽  
Giacomo Bonaccorsi ◽  
Francesco Braghin
Keyword(s):  
Rigid Bodies ◽  
Design Tool ◽  
Mems Devices ◽  
Efficient Design ◽  
Computationally Efficient ◽  
Design Environment ◽  
Parametric Generation ◽  
Design And Optimization ◽  
Gradient Based ◽  
Complex Models

In this paper, we propose a novel design and optimization environment for inertial MEMS devices based on a computationally efficient schematization of the structure at the a device level. This allows us to obtain a flexible and efficient design optimization tool, particularly useful for rapid device prototyping. The presented design environment—feMEMSlite—handles the parametric generation of the structure geometry, the simulation of its dynamic behavior, and a gradient-based layout optimization. The methodology addresses the design of general inertial MEMS devices employing suspended proof masses, in which the focus is typically on the dynamics associated with the first vibration modes. In particular, the proposed design tool is tested on a triaxial beating-heart MEMS gyroscope, an industrially relevant and adequately complex example. The sensor layout is schematized by treating the proof masses as rigid bodies, discretizing flexural springs by Timoshenko beam finite elements, and accounting for electrostatic softening effects by additional negative spring constants. The MEMS device is then optimized according to two possible formulations of the optimization problem, including typical design requirements from the MEMS industry, with particular focus on the tuning of the structural eigenfrequencies and on the maximization of the response to external angular rates. The validity of the proposed approach is then assessed through a comparison with full FEM schematizations: rapidly prototyped layouts at the device level show a good performance when simulated with more complex models and therefore require only minor adjustments to accomplish the subsequent physical-level design.

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