Unsteady Propulsor Force Prediction for Spatially and Temporally Varying Inflow

2002 ◽  
Author(s):  
Stephen A. Huyer ◽  
Stephen R. Snarski
Keyword(s):  
Experimental Data ◽  
Three Dimensional ◽  
Axial Direction ◽  
Time Varying ◽  
Massachusetts Institute Of Technology ◽  
Mean Flow ◽  
Turbulent Inflow ◽  
Turbulent Characteristics ◽  
Unsteady Force ◽  
Institute Of Technology

A method to compute unsteady propulsor forces for spatially and temporally varying inflows is presented. A propulsor flow prediction code, previously developed by the Massachusetts Institute of Technology, was modified and upgraded to account for time varying inflow and multiple blade rotations. The original code utilizes lifting surface theory and discretizes the propulsor surface as boundary elements to compute the unsteady potential flow. Experimental data characterizing the full unsteady, three-dimensional turbulent inflow to a Swirl-Induced Stator Upstream of Propulsor (SISUP) propulsor, were used as inflow boundary conditions. Experimental data recorded the periodic velocity fluctuations due to the stator wakes as well as the broadband turbulent characteristics of the inflow. Blade force, integrated shaft force, and blade pressure are computed based on the experimental inflow. The effect of periodic variations in the inflow was examined to determine the effect on unsteady blade forces. For these cases, the time mean experimental effective inflow is used and a fluctuating component is added for flow in the axial direction. This may be viewed as an effectively fluctuating freestream. Comparisons of unsteady force and radiated noise are then made with the baseline mean flow case to gauge the time-varying effects. Fluctuating velocity dramatically altered the force spectra even at frequencies different from the velocity fluctuation frequency. This modified algorithm can now be utilized to examine a wider set of time-dependent propulsor flow problems and to calculate the associated performance due to these unsteady flows.

scholarly journals Three-Dimensional Turbulent Vortex Shedding From a Surface-Mounted Square Cylinder: Predictions With Large-Eddy Simulations and URANS

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
B. A. Younis ◽  
A. Abrishamchi
Keyword(s):  
Experimental Data ◽  
Turbulence Model ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Large Eddy Simulations ◽  
Navier Stokes ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Navier Stokes Equations ◽  
Large Eddy

The paper reports on the prediction of the turbulent flow field around a three-dimensional, surface mounted, square-sectioned cylinder at Reynolds numbers in the range 104–105. The effects of turbulence are accounted for in two different ways: by performing large-eddy simulations (LES) with a Smagorinsky model for the subgrid-scale motions and by solving the unsteady form of the Reynolds-averaged Navier–Stokes equations (URANS) together with a turbulence model to determine the resulting Reynolds stresses. The turbulence model used is a two-equation, eddy-viscosity closure that incorporates a term designed to account for the interactions between the organized mean-flow periodicity and the random turbulent motions. Comparisons with experimental data show that the two approaches yield results that are generally comparable and in good accord with the experimental data. The main conclusion of this work is that the URANS approach, which is considerably less demanding in terms of computer resources than LES, can reliably be used for the prediction of unsteady separated flows provided that the effects of organized mean-flow unsteadiness on the turbulence are properly accounted for in the turbulence model.

CFD analysis of the effect of nozzle stand-off distance on turbulent impinging jets

2013 ◽  
Vol 40 (7) ◽  
pp. 603-612 ◽  
Author(s):  
Mehrdad Shademan ◽  
Ram Balachandar ◽  
Ronald M. Barron
Keyword(s):  
Experimental Data ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Axial Direction ◽  
Reynolds Stress Model ◽  
Impinging Jets ◽  
Diameter Ratio ◽  
Wall Region ◽  
Nozzle Height ◽  
Jet Characteristics

Three-dimensional steady Reynolds Averaged Navier-Stokes simulations have been carried out to investigate the effect of the nozzle stand-off distance on the mean and turbulence characteristics of jets impinging vertically on flat surfaces. As part of the study, the performance of different turbulence models such as Realizable k–ε, k–ω SST, and Reynolds Stress Model (RSM) were evaluated. Based on comparisons with experimental data, RSM was chosen to further evaluate the characteristics of impinging jets. The Reynolds number based on the jet exit velocity and nozzle diameter is 100 000. Three different nozzle height-to-diameter ratios, representing different types of impinging jets, were simulated and compared with available experimental data. A strong dependency of the jet characteristics on the nozzle height-to-diameter ratio was observed. The simulations show that an increase in this ratio results in larger shear stress and more distributed pressure on the wall, more development of the flow in the axial direction and faster progress of the jet in the wall region. The current simulations present a robust step-by-step computational fluid dynamics approach to investigate the role of the nozzle height-to-diameter ratio on the impinging jet flow parameters.

scholarly journals Development of 3D boundary element method for the simulation of acoustic metamaterials/metasurfaces in mean flow for aerospace applications

2020 ◽  
Vol 19 (6-8) ◽  
pp. 324-346
Author(s):  
Imran Bashir ◽  
Michael Carley
Keyword(s):  
Experimental Data ◽  
Mach Number ◽  
Boundary Element Method ◽  
Boundary Element ◽  
Sound Propagation ◽  
Three Dimensional ◽  
Boundary Integral ◽  
Mean Flow ◽  
Low Mach Number ◽  
Element Method

Low-cost airlines have significantly increased air transport, thus an increase in aviation noise. Therefore, predicting aircraft noise is an important component for designing an aircraft to reduce its impact on environmental noise along with the cost of testing and certification. The aim of this work is to develop a three-dimensional Boundary Element Method (BEM), which can predict the sound propagation and scattering over metamaterials and metasurfaces in mean flow. A methodology for the implementation of metamaterials and metasurfaces in BEM as an impedance patch is presented here. A three-dimensional BEM named as BEM3D has been developed to solve the aero-acoustics problems, which incorporates the Fast Multipole Method to solve large scale acoustics problems, Taylor’s transformation to account for uniform and non-uniform mean flow, impedance and non-local boundary conditions for the implementation of metamaterials. To validate BEM3D, the predictions have been benchmarked against the Finite Element Method (FEM) simulations and experimental data. It has been concluded that for no flow case BEM3D gives identical acoustics potential values against benchmarked FEM (COMSOL) predictions. For Mach number of 0.1, the BEM3D and FEM (COMSOL) predictions show small differences. The difference between BEM3D and FEM (COMSOL) predictions increases further for higher Mach number of 0.2 and 0.3. The increase in difference with Mach number is because Taylor’s Transformation gives an approximate solution for the boundary integral equation. Nevertheless, it has been concluded that Taylor’s transformation gives reasonable predictions for low Mach number of up to 0.3. BEM3D predictions have been validated against experimental data on a flat plate and a duct. Very good agreement has been found between the measured data and BEM3D predictions for sound propagation without and with the mean flow at low Mach number.

Etude comparative de deux modèles mathématiques dans l'analyse de rejets thermiques à Gentilly

1976 ◽  
Vol 3 (1) ◽  
pp. 119-125
Author(s):  
Claude Marche ◽  
Luc Robillard
Keyword(s):  
Three Dimensional ◽  
Aerial Survey ◽  
Hot Water ◽  
Lateral Spread ◽  
Two Dimensional ◽  
Massachusetts Institute Of Technology ◽  
Dimensional Model ◽  
Dimensional Approach ◽  
Three Dimensional Model ◽  
Institute Of Technology

On August 8th 1974, infrared photographic data of the hot water plume at the Gentilly nuclear powerplant were obtained from an aerial survey of the St. Lawrence River. Important parameters such as the longitudinal decrease of temperature or lateral spread of the rejected water become available together with hydraulic and thermal ambient conditions.At first, a three-dimensional model, already developed at the Massachusetts Institute of Technology, was applied to the actual volume of water rejected and predicted a dilution rate much higher than the actual one. The use of a different geometric scheme has reduced the gap between predicted and actual values. The same scheme has been tried on a two-dimensional model. The two-dimensional approach is justified by consideration of the bottom topography.The discussion of results concerns: first, the establishment of an adequate geometric scheme and second, the error brought by the two-dimensional approach.

Transitional and Turbulent Flow Modeling in a Tesla Valve

2013 ◽  
Author(s):  
Scott M. Thompson ◽  
Tausif Jamal ◽  
Basil J. Paudel ◽  
D. Keith Walters
Keyword(s):  
Experimental Data ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Flow Speed ◽  
Flow Modeling ◽  
Ansys Fluent ◽  
Local Flow ◽  
Turbulent Characteristics ◽  
Minor Losses ◽  
Tesla Valve

A Tesla valve is a fluidic dioide that may be used in a variety of mini/micro channel applications for passive flow rectification and/or control. The valve’s effectiveness is quantified by the diodicity, which is primarily governed by the incoming flow speed, its design and direction-dependent minor losses throughout its structure during forward and reverse flows. It has been previously shown that the Reynolds number at the valve inlet is not representative of the entire flow regime throughout the Tesla structure. Therefore, pure-laminar solving methods are not necessarily accurate. Local flow instabilities exist and exhibit both transitional and turbulent characteristics. Therefore, the current investigation seeks to identify a suitable RANS-based flow modeling approach to predict Tesla valve diodicity via three-dimensional (3D) computational fluid dynamics (CFD) for inlet Reynolds numbers up to Re = 2,000. Using ANSYS FLUENT (v. 14), a variety of models were employed, including: the Realizable k-ε, k-kL-ω and SST k-ω models. All numerical simulations were validated against available experimental data obtained from an identically-shaped Tesla valve structure. It was found that the k-ε model drastically under-predicts experimental data for the entire range of Reynolds numbers investigated and cannot accurately model the Tesla valve flow. The k-kL-ω and SST k-ω models approach the experimentally-measured diodicity better than regular 2D CFD. The k-kL-ω demonstrates exceptional agreement with experimental data for Reynolds numbers up to approximately 1,500. However, both the k-kL-ω and k-ω SST models over-predict experimental data for Re = 2,000.

scholarly journals Prediction of Small Rotating Stall in Axial Compressors Using Actuator Disc Theory

1985 ◽  
Author(s):  
K. Mathioudakis
Keyword(s):  
Experimental Data ◽  
Perturbation Analysis ◽  
Theoretical Study ◽  
Three Dimensional ◽  
Rotating Stall ◽  
Mean Flow ◽  
Axial Compressors ◽  
Blade Row ◽  
Rotating Reference Frame ◽  
Actuator Disc

A theoretical study of the development of rotating stall in axial compressors is presented. A small perturbation analysis is used for this purpose. The compressor is considered as a series of vaneless spaces and blade rows. The axisymmetric mean flow is of the free vortex type and blade rows are represented as actuator discs. The perturbations are three dimensional and steady with respect to a rotating reference frame. For high hub-tip ratio annuli the transfer relations for the perturbations are expressed in a matrix form. This formulation allows the prediction of the occurrence and development of rotating stall in single or multiple blade row configurations. The results of the prediction compare favourably with experimental data.

scholarly journals A Validation Study of the Aerodynamic Behaviour of a Wind Turbine: Three-Dimensional Rotational Case

CFD letters ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1-12
Author(s):  
Khaoula Qaissi ◽  
Omer Elsayed ◽  
Mustapha Faqir ◽  
Elhachmi Essadiqi
Keyword(s):  
Experimental Data ◽  
Wind Turbine ◽  
Validation Study ◽  
Three Dimensional ◽  
Wind Speeds ◽  
Turbulent Inflow ◽  
Attached Flow ◽  
Computational Fluid Dynamics Cfd ◽  
Variable Wind ◽  
Separating Flows

Numerical modelling and simulation of a rotating, tapered, and twisted three-dimensional blade with turbulent inflow conditions and separating flows is a challenging case in Computational Fluid Dynamics (CFD). The numerical simulation of the fluid flow behaviour over a wind turbine blade is important for the design of efficient machines. This paper presents a numerical validation study using the experimental data collected by the National Renewable Energy Laboratory (NREL). All the simulations are performed on the sequence S of the extensive experimental sequences conducted at the NASA/Ames wind tunnel with constant RPM and variable wind speeds. The results show close agreement with the NREL UAE experimental data. The CFD model captures closely the totality of the defining quantities. The shaft torque is well-predicted pre-stall but under-predicted in the stall region. The three-dimensional flow and stall are well captured and demonstrated in this paper. Results show attached flow in the pre-stall region. The separation appears at a wind speed of 10 m/s near the blade root. For V>10m/s, the blade appears to experience a deep stall from root to tip.

scholarly journals The effect of oscillating turbulent inflow on the shape of downstream turbulence

2021 ◽  
Author(s):  
Young-Woo Yi ◽  
◽  
Bhupendra Singh Chauhan ◽  
Hee-Chang Lim ◽  
◽  
...  
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Inlet Section ◽  
Mean Flow ◽  
Turbulent Inflow ◽  
Turbulent Statistics ◽  
Large Eddy ◽  
The Mean

Large Eddy Simulations (LES) has been widely applied and used in several decades to simulate a turbulent boundary layer in the numerical domain. In this study, we aimed to make a synthetic inflow generator (SIG) yielding an appropriate property of turbulent boundary layer in the inlet section and making quick development in the downstream of a three-dimensional domain. In order to achieve turbulent boundary layer quickly in a limited domain, the oscillating term was implemented in the well-defined boundary layer, which was expected to make faster convergence in the calculation. Cholesky decomposition was also applied to possess turbulent statistics such as the randomness and correlation of turbulent flow. In a result, the oscillating inflow did not show the faster convergence, but it indicated a possibility to improve statistical quantities in the downstream. In addition, regarding the mean flow characteristics were very close to the calculation without the oscillating flow. On the other hand, the turbulent statistics were improved depending on the oscillating magnitude.

Modeling of Propeller Cavitation on Merchant Vessels

1982 ◽  
Vol 19 (01) ◽  
pp. 37-51
Author(s):  
Leslie M. Gray ◽  
David S. Greeley
Keyword(s):  
Input Data ◽  
Tip Vortex ◽  
Analytical Models ◽  
Time Varying ◽  
Massachusetts Institute ◽  
Massachusetts Institute Of Technology ◽  
Marine Propeller ◽  
Tip Vortex Cavitation ◽  
Propeller Design ◽  
Institute Of Technology

The time-varying cavitation on a marine propeller, which excites hull vibrations, is calculated. The analytical model is exercised to guide propeller design and operation in order to minimize this type of hull excitation. This model, as well as a more elaborate model under development at Massachusetts Institute of Technology, is compared with recent full-scale observations of propeller cavitation. The paper illustrates the importance of both accurate input data on scaled vessel wake velocities and the inclusion, in analytical models, of tip vortex cavitation.

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