Modular Turbulence Modelling Applied to an Engine Intake

2013 ◽  
Author(s):  
Ugochukwu R. Oriji ◽  
Paul G. Tucker
Keyword(s):  
Surface Roughness ◽  
Richardson Number ◽  
Eddy Viscosity ◽  
Fluid Dynamic ◽  
Test Cases ◽  
Laminar Separation ◽  
Streamline Curvature ◽  
Flow Features ◽  
Unsteady Rans ◽  
The One

The one equation Spalart Allamaras (SA) turbulence model in an extended modular form is employed for the prediction of cross wind flow around the lip of a 90 degree sector of an intake with and without surface roughness. The flow features around the lip are complex. There exists a region of high streamline curvature. For this the Richardson number would suggest complete degeneration to laminar flow. Also there are regions of high favourable pressure gradient (FPG) sufficient to laminarize a turbulent boundary layer (BL). This is all terminated by a shock and followed by a laminar separation. Under these severe conditions, the SA model is insensitive to capturing the effects of laminarization and the reenergization of eddy viscosity which promotes the momentum transfer and correct reattachment prior to the fan face. Through distinct modules, the SA model has been modified to account for the effect of laminarization and separation induced transition. The SA modules have been implemented in Rolls-Royce HYDRA Computational Fluid Dynamic (CFD) solver. They have been validated over a number of experimental test cases involving laminarization and also surface roughness. The validated modules are finally applied in unsteady RANS mode to flow around an engine intake and comparisons made with measurements. Encouraging agreement is found and hence advances made towards a more reliable intake design framework.

Modular Turbulence Modeling Applied to an Engine Intake

2013 ◽  
Vol 136 (5) ◽  
Author(s):  
Ugochukwu R. Oriji ◽  
Paul G. Tucker
Keyword(s):  
Surface Roughness ◽  
Turbulence Modeling ◽  
Fluid Dynamic ◽  
Navier Stokes ◽  
Test Cases ◽  
Laminar Separation ◽  
Streamline Curvature ◽  
Favorable Pressure Gradient ◽  
Flow Features ◽  
The One

The one equation Spalart–Allmaras (SA) turbulence model in an extended modular form is presented. It is employed for the prediction of crosswind flow around the lip of a 90 deg sector of an intake with and without surface roughness. The flow features around the lip are complex. There exists a region of high streamline curvature. For this, the Richardson number would suggest complete degeneration to laminar flow. Also, there are regions of high favorable pressure gradient (FPG) sufficient to laminarize a turbulent boundary layer (BL). This is all terminated by a shock and followed by a laminar separation. Under these severe conditions, the SA model is insensitive to capturing the effects of laminarization and the reenergization of eddy viscosity. The latter promotes the momentum transfer and correct reattachment prior to the fan face. Through distinct modules, the SA model has been modified to account for the effect of laminarization and separation induced transition. The modules have been implemented in the Rolls-Royce HYDRA computational fluid dynamic (CFD) solver. They have been validated over a number of experimental test cases involving laminarization and also surface roughness. The validated modules are finally applied in unsteady Reynolds-averaged Navier–Stokes (URANS) mode to flow around an engine intake and comparisons made with measurements. Encouraging agreement is found and hence advances made towards a more reliable intake design framework.

A Three-Equation Variant of the SST k-ω Model Sensitized to Rotation and Curvature Effects

2011 ◽  
Vol 133 (11) ◽  
Author(s):  
Tej P. Dhakal ◽  
D. Keith Walters
Keyword(s):  
Fluid Flow ◽  
Transport Equation ◽  
Rotation Rate ◽  
Eddy Viscosity ◽  
Test Cases ◽  
New Model ◽  
Streamline Curvature ◽  
Curvature Effects ◽  
Velocity Scale ◽  
Heat And Fluid Flow

A new variant of the SST k-ω model sensitized to system rotation and streamline curvature is presented. The new model is based on a direct simplification of the Reynolds stress model under weak equilibrium assumptions [York et al., 2009, “A Simple and Robust Linear Eddy-Viscosity Formulation for Curved and Rotating Flows,” International Journal for Numerical Methods in Heat and Fluid Flow, 19(6), pp. 745–776]. An additional transport equation for a transverse turbulent velocity scale is added to enhance stability and incorporate history effects. The added scalar transport equation introduces the physical effects of curvature and rotation on turbulence structure via a modified rotation rate vector. The modified rotation rate is based on the material rotation rate of the mean strain-rate based coordinate system proposed by Wallin and Johansson (2002, “Modeling Streamline Curvature Effects in Explicit Algebraic Reynolds Stress Turbulence Models,” International Journal of Heat and Fluid Flow, 23, pp. 721–730). The eddy viscosity is redefined based on the new turbulent velocity scale, similar to previously documented k-ɛ- υ2 model formulations (Durbin, 1991, “Near-Wall Turbulence Closure Modeling without Damping Functions,” Theoretical and Computational Fluid Dynamics, 3, pp. 1–13). The new model is calibrated based on rotating homogeneous turbulent shear flow and is assessed on a number of generic test cases involving rotation and/or curvature effects. Results are compared to both the standard SST k-ω model and a recently proposed curvature-corrected version (Smirnov and Menter, 2009, “Sensitization of the SST Turbulence Model to Rotation and Curvature by Applying the Spalart-Shur Correction Term,” ASME Journal of Turbomachinery, 131, pp. 1–8). For the test cases presented here, the new model provides reasonable engineering accuracy without compromising stability and efficiency, and with only a small increase in computational cost.

Performance Analysis of Multi-Sectional Cycloidal Hydrokinetic Turbines

2021 ◽  
Author(s):  
Ang Li ◽  
Yijie Wang ◽  
Jun Chen ◽  
Greg Jensen ◽  
Haiyan Zhang
Keyword(s):  
Fluid Dynamic ◽  
Power Coefficient ◽  
Cfd Simulations ◽  
Hydrokinetic Turbines ◽  
Turbine Efficiency ◽  
Reliable Source ◽  
Sliding Interfaces ◽  
Water Turbine ◽  
Unsteady Rans ◽  
The One

Abstract Hydrokinetic power is the most efficient and reliable source of renewable energy and it has been utilized to produce power for centuries. The cycloidal water turbine is a subset of the H-bar type Darrieus turbines that are designed to actively controls the pitch angle of blades to improve turbine efficiency. However, the traditional cycloidal turbine has some shortcomings. For example, the torque and power coefficient vary significantly as the turbine rotates, which means the produced power is not uniform in one revolution. The associated hydrodynamic load will lead to fatigue of the turbine structure that will shorten the turbine lifespan. To solve this problem, a concept of the multi-sectional cycloidal water turbine is proposed. In the present study, computational fluid dynamic (CFD) simulations are applied to investigate the performance of the multi-sectional cycloidal turbine. A cycloidal turbine with three identical sections is designed. Each section consists of three blades and NACA0021 is chosen as the hydrofoil. Structured mesh with sliding interfaces is generated and arbitrary Mesh Interface (AMI) technique is employed. Unsteady RANS simulations with SST k–ω model are conducted to compute the flow field and torque generated by the turbine, and then power coefficient is computed. The results demonstrates that the three-section turbine has uniform performance in one revolution. At the design condition, the power coefficients of the one-section turbine and the three-section turbine are similar; when the TSR is much larger or less than the desired value, the three-section turbine has better performance.

Numerical Studies on Cavitation and Surface Roughness

2019 ◽  
Vol 793 ◽  
pp. 79-84 ◽  
Author(s):  
Jithin Ambarayil Joy ◽  
Vijayakumar Mathaiyan ◽  
Muhammad Sajjad ◽  
Dong Won Jung
Keyword(s):  
Biological Sciences ◽  
Surface Roughness ◽  
Parametric Analysis ◽  
Smooth Surface ◽  
Material Surface ◽  
Cavitation Damage ◽  
Numerical Studies ◽  
Flow Features ◽  
The One ◽  
Topical Interest

The study of cavitation is of topical interest in both physical and biological sciences. The surface roughness changes the effect of cavitation on a material surface. Due to cavitation, the material with low surface roughness value has relatively more damage, when compared to the one with higher value. In this paper, preliminary numerical studies are carried on cavitation and surface roughness. As a part of the code validation and calibration, the numerically predicted boundary-layer blockage at the Sanal flow choking condition for the channel flow is verified using the closed-form analytical model of V.R. Sanal Kumar et al. (AIP Advances, 8, 025315, 2018) at various surface roughness and found excellent agreement with the exact solution. Parametric analytical studies are carried out for examining the flow features at two different surface roughness and turbulence levels. We noticed that the wavy surface with small waves increases the Nussle number, therefore it is also considered for parametric analysis. Considering the defect-free smooth surface material, we presumed that the cavitation damage in the smooth surface is more than the rough surface because the smooth surface can generate more micro bubbles. These micro bubbles grow into macro bubbles which in turn results in cavitation. This study is a pointer towards for formulating various industrial topics with fluid-structural interaction problems for getting plausible solutions for meeting the needs of various industries.

An Eddy-Viscosity Model Sensitized to Curvature and Wall-Roughness Effects for Reynolds-Averaged Closure

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Yang Zhang ◽  
Gang Chen ◽  
Jiakuan Xu
Keyword(s):  
Richardson Number ◽  
Eddy Viscosity ◽  
Plane Channel ◽  
Wall Roughness ◽  
Roughness Effects ◽  
New Model ◽  
Streamline Curvature ◽  
Eddy Viscosity Model ◽  
System Rotation ◽  
Rotating Channel

Abstract This paper presents a new extension of the realizable K−ε model that accounts for streamline curvature, system rotation, and surface roughness. The model is a type of realizable K−ε model, but the transport equations and the eddy-viscosity damping functions are modified, based on the Richardson number and roughness height; the roughness correction covers both the transitional and fully rough regimes. Flows in a rotating channel and a U-bend duct are used to validate the response of the new model to the system rotation and streamline curvature. The flow in a plane channel and the flow over a dune are used to validate the roughness extension. Finally, a rotating channel with rough walls is studied, to test the new model when both rotation and roughness are present.

scholarly journals Deep Learning Approach for Vibration Signals Applications

Sensors ◽  
2021 ◽  
Vol 21 (11) ◽  
pp. 3929
Author(s):  
Han-Yun Chen ◽  
Ching-Hung Lee
Keyword(s):  
Surface Roughness ◽  
Tool Wear ◽  
Parameters Optimization ◽  
Frequency Spectra ◽  
Vibration Signals ◽  
Bearing Faults ◽  
Time Frequency ◽  
And Performance ◽  
The One ◽  
Short Time

This study discusses convolutional neural networks (CNNs) for vibration signals analysis, including applications in machining surface roughness estimation, bearing faults diagnosis, and tool wear detection. The one-dimensional CNNs (1DCNN) and two-dimensional CNNs (2DCNN) are applied for regression and classification applications using different types of inputs, e.g., raw signals, and time-frequency spectra images by short time Fourier transform. In the application of regression and the estimation of machining surface roughness, the 1DCNN is utilized and the corresponding CNN structure (hyper parameters) optimization is proposed by using uniform experimental design (UED), neural network, multiple regression, and particle swarm optimization. It demonstrates the effectiveness of the proposed approach to obtain a structure with better performance. In applications of classification, bearing faults and tool wear classification are carried out by vibration signals analysis and CNN. Finally, the experimental results are shown to demonstrate the effectiveness and performance of our approach.

scholarly journals Experimental Investigation and Comparison of the Thermal Performance of Additively and Conventionally Manufactured Heat Exchangers

Metals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 574
Author(s):  
Ana Vafadar ◽  
Ferdinando Guzzomi ◽  
Kevin Hayward
Keyword(s):  
Surface Roughness ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
High Efficiency ◽  
Cooling System ◽  
Fluid Dynamic ◽  
Dynamic Performance ◽  
Experimental Studies ◽  
Manufacturing Method ◽  
Industrial Sectors

Air heat exchangers (HXs) are applicable in many industrial sectors because they offer a simple, reliable, and cost-effective cooling system. Additive manufacturing (AM) systems have significant potential in the construction of high-efficiency, lightweight HXs; however, HXs still mainly rely on conventional manufacturing (CM) systems such as milling, and brazing. This is due to the fact that little is known regarding the effects of AM on the performance of AM fabricated HXs. In this research, three air HXs comprising of a single fin fabricated from stainless steel 316 L using AM and CM methods—i.e., the HXs were fabricated by both direct metal printing and milling. To evaluate the fabricated HXs, microstructure images of the HXs were investigated, and the surface roughness of the samples was measured. Furthermore, an experimental test rig was designed and manufactured to conduct the experimental studies, and the thermal performance was investigated using four characteristics: heat transfer coefficient, Nusselt number, thermal fluid dynamic performance, and friction factor. The results showed that the manufacturing method has a considerable effect on the HX thermal performance. Furthermore, the surface roughness and distribution, and quantity of internal voids, which might be created during and after the printing process, affect the performance of HXs.

scholarly journals Reynolds averaged turbulence modelling using deep neural networks with embedded invariance

2016 ◽  
Vol 807 ◽  
pp. 155-166 ◽  
Author(s):  
Julia Ling ◽  
Andrew Kurzawski ◽  
Jeremy Templeton
Keyword(s):  
Neural Network ◽  
Neural Networks ◽  
Reynolds Stress ◽  
Network Architecture ◽  
Eddy Viscosity ◽  
Deep Neural Networks ◽  
Test Cases ◽  
Neural Network Architecture ◽  
Stress Anisotropy ◽  
Anisotropy Tensor

There exists significant demand for improved Reynolds-averaged Navier–Stokes (RANS) turbulence models that are informed by and can represent a richer set of turbulence physics. This paper presents a method of using deep neural networks to learn a model for the Reynolds stress anisotropy tensor from high-fidelity simulation data. A novel neural network architecture is proposed which uses a multiplicative layer with an invariant tensor basis to embed Galilean invariance into the predicted anisotropy tensor. It is demonstrated that this neural network architecture provides improved prediction accuracy compared with a generic neural network architecture that does not embed this invariance property. The Reynolds stress anisotropy predictions of this invariant neural network are propagated through to the velocity field for two test cases. For both test cases, significant improvement versus baseline RANS linear eddy viscosity and nonlinear eddy viscosity models is demonstrated.

Novel Perturbation Analysis for a Widely Applicable Curvature Law of the Wall

1999 ◽  
Author(s):  
Namhyo Kim ◽  
David L. Rhode
Keyword(s):  
Perturbation Analysis ◽  
Richardson Number ◽  
Perturbation Technique ◽  
Solution Approach ◽  
Law Of The Wall ◽  
Streamline Curvature ◽  
Curvature Effects ◽  
Gradient Richardson Number ◽  
Closed Form Analytical Solution ◽  
First Time

Abstract A streamline curvature law of the wall is analytically derived to include very strong curved-channel wall curvature effects through a novel perturbation analysis. The new law allows improved analysis of such flows, and it provides the basis for improved wall function boundary conditions for their computation (CFD) over a wider range of y+, even for very strong curvature cases. The unique derivation is based on the Boussinesq eddy viscosity and curvature-corrected mixing length concepts, which is a linear function of the gradient Richardson number. For the first time, to include more complete curved flow physics, local streamline curvature effects in the gradient Richardson number are kept. To overcome the mathematical difficulty of keeping all of these local streamline curvature terms, a novel perturbation solution approach is successfully developed. This novel perturbation technique allows a closed-form analytical solution to many similar non-linear problems which previously required more complicated techniques. Qualitative and quantitative comparisons with measurements and previous curvature laws of the wall obtained by different approaches reveal that the new law shows improved representation of the wall curvature effects for all of the four test cases.

Blade Fault Recognition Based on Signal Processing and Adaptive Fluid Dynamic Modelling

1997 ◽  
Author(s):  
A. Stamatis ◽  
N. Aretakis ◽  
K. Mathioudakis
Keyword(s):  
Flow Field ◽  
Fluid Dynamic ◽  
Measurement Data ◽  
Dynamic Modelling ◽  
Physical Modelling ◽  
Diagnostic Procedures ◽  
Measured Quantity ◽  
Test Cases ◽  
Actual Measurement ◽  
Fault Recognition

An approach for identification of faults in blades of a gas turbine, based on physical modelling is presented. A measured quantity is used as an input and the deformed blading configuration is produced as an output. This is achieved without using any kind of “signature”, as is customary in diagnostic procedures for this kind of faults. A fluid dynamic model is used in a manner similar to what is known as “inverse design methods”: the solid boundaries which produce a certain flow field are calculated by prescribing this flow field. In the present case a signal, corresponding to the pressure variation on the blade-to-blade plane, is measured. The blade cascade geometry that has produced this signal is then produced by the method. In the paper the method is described and applications to test cases are presented. The test cases include theoretically produced faults as well as experimental cases, where actual measurement data are shown to produce the geometrical deformations which existed in the test engine.

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