Moving Reference Frame Approach Research Articles

Experimental and numerical study on the influence of flow passages in centrifugal fan using computational fluid dynamics

In this work, three actual impeller geometries of identical size, with backward, radial, and forward flow passages in the same volute casing, are experimentally analysed and numerically simulated to understand the flow physics characteristics and the performance mapping under different flowrate conditions. A grid independence test is carried out for the whole computational domain to capture complex flow behaviour inside blades. The three-dimensional numerical analysis is performed under steady flow conditions, and for a rotational domain, a moving reference frame approach (frozen rotor method) is used. The results obtained from experimental and simulated cases for backward, radial, and forward curved centrifugal fans with varying mass flowrates shows that static pressure and total pressure are increased with an increase in rotation speed and the static pressure gradient is higher in forward curved blades than in backward and radial bladed centrifugal fans. A blade’s low and high-pressure regions along the suction and pressure sides are visualised by numerical analysis. The degree of recirculation within blade passages, flow reversal and vortex formation in volute and tongue regions is observed to be different in all three types of flow passages, which clearly describes its influence on the performance characteristics of centrifugal fans.

Effect of biofouling roughness on the full-scale powering performance of a submarine

The aim of this study is to investigate the impact of barnacle type biofouling roughness on the full-scale powering performance of a submarine in calm seas. The importance of the diversified biofouling accumulations in terms of hull location is also examined over the submarine hull by implementing homogeneous and heterogenous roughness distribution. In this study, a Reynolds Averaged Navier Stokes (RANS) based CFD model was used for predicting the effects of biofouling roughness on the self-propulsion characteristics for the full-scale submarine form. The powering performance analyses are performed with discretised propeller geometry, and the Moving Reference Frame approach is used to model the rotational motion of the propeller. A proportional-integral (PI) approach is adopted to obtain the self-propulsion point efficiently by modifying the propeller's rotational speed. First, the resistance and the self-propulsion characteristics of the model scale submarine are validated with the experimental and other numerical studies in the literature. Following this validation task, a roughness function model is employed within a CFD software's wall function to represent the rough surfaces over the submarine hull. The results showed that although roughness has a varying effect on the submarine's self-propulsion characteristics depending on the roughness distribution, it increases the hull resistance and, hence, the delivered power overall. Roughness on the forward section of the hull has a more pronounced effect on the resistance and delivered power. The study demonstrated that the presence of partial hull fouling should not be ignored, and required precautions should be taken to prevent losses in submarine performance, especially for the fouling at the forward section of the submarine.

RETRACTED ARTICLE: Numerical investigation to observe combined effect of propeller boss cap fin (PBCF) and propeller duct to improve propeller efficiency

Propeller is the main device in marine vehicle to generate propulsive energy. During practical manoeuvring condition, it losses a major part of energy due to the formation of hub as well as tip vortex. This fact becomes a great concern for researcher and motivates to find some alternate energy saving device (ESD). In this paper numerical investigations, based on Reynolds Average Navier Stokes (RANS) equation, are carried out to observe the combined effect of PBCF and propeller duct as ESDs to improve propeller efficiency. Here, aerofoil shape PBCF with NACA4412 profile has been combined with 19A and 19Am duct to observe their ability to improve propeller efficiency in moving reference frame approach. Along that to make a comparative study, numerical investigations are also performed with propeller and 19A duct without PBCF. Results show that in comparison to the combined effect of PBCF and ducted propeller, only duct (19A) without PBCF plays a prominent role to enhance propeller efficiency by approximately 9.21%. To obtain more details of flow phenomenon, fluctuation of velocity, pressure, vortex strength, etc., at various locations are also investigated. Besides that, the effect of angle of attack of the duct on a PBCF introduced ducted propeller is also investigated numerically.

VIV modelled using simplified cable dynamics coupled to sub-critical cylinder flow simulations in a moving reference frame

This work focuses on the study of the phenomenon of vortex-induced vibrations in overhead lines under the effect of weak winds. Full three-dimensional simulation is not feasible because of the high length to width aspect ratios of the overhead lines. Thus a quasi-3D method based on strip theory is adopted in this work. This method decouples the system of interactions between the overhead line and the wind into a series of sub-systems. The fluid flow in each sub-system is represented as a series of independent rigid oscillating cylinder flows that are only coupled through the transmission line model. To avoid the use of a moving mesh for the fluid domain, a moving reference frame approach is employed. In this approach, the coordinate axes of the flow simulation are attached to the oscillating cylinder and an acceleration term in the flow equations accounts for the cable motion. Moreover, in order to take into account the turbulent effect in the flow, turbulence models, including RANS, LES and DES, are evaluated for the present application involving flows in the sub-critical regime. Finally, numerical test cases are performed in order to validate the turbulence models and the moving reference frame approach, then cable dynamics test cases are conducted to validate the quasi-3D method.

Numerical investigation on the flow characteristics and hydrodynamic performance of tandem propeller

The hydrodynamic performance of tandem propeller (two co-rotating KP458 propellers) is investigated by an FVM (Finite Volume Method) based approach in this study. The effects of advance ratio J (0 ≤ J ≤ 0.7), spacing ratio (0.26 ≤ L/Df ≤ 0.34) and diameter ratio (0.92 ≤ Da/Df ≤ 0.97) are comprehensively studied and analyzed. A three-dimensional cubic computational domain is considered in this study, and the MRF (Moving Reference Frame) approach is adopted to handle the rotation of the tandem propeller mathematically. Turbulence is accounted for with the RNG k-ε model. It is demonstrated that the hydrodynamic forces maximize at a spacing ratio of 0.29 if the diameter ratio equals 1.0. It is also found that the efficiency is improved by approximately 45% for the tandem propeller with the diameter ratio being 0.95 at L/Df = 0.29, compared to the single propeller, at J = 0.7. In addition, by appropriately specifying the spacing ratio or the diameter ratio, the rotation of rear propeller could well absorb the energy of the trailing vortices shed from the front propeller. Consequently, the trailing vortices are rapidly dissipated and disappear in the wake field after merging, and a better hydrodynamic performance can be obtained.

A semi-empirical multi-degree of freedom body force propeller model

Efficient and accurate modelling of a self-propelled vessel in a large amplitude seaway with CFD-based numerical methods is a challenging task and is prohibitively expensive for most designers and engineers. Viscous CFD methods can accurately model viscous effects, but the small numerical time step required to analyze the rotating propeller leads to a large computational cost. A method for efficiently and accurately modelling the six degree of freedom force on the propeller is required to feasibly model a self propelled vessel maneuvering in a high amplitude seaway. This paper outlines the framework for developing an unsteady body force propeller model for unsteady conditions. The purpose of this study is to train a semi-empirical algorithm to accurately prescribe the unsteady body force to model the propeller. The MOERI Container ship propeller is analyzed with RANS CFD. Open water data is compared to the RANS CFD results of a steady Moving Reference Frame approach. Unsteady surge and propeller revolution rate are applied to a transient rotating mesh model in open water and behind condition. The predictions of the algorithm match well with the CFD results.

A comparative study of RANS-based turbulence models for an upscale wind turbine blade

Computational fluid dynamic (CFD) numerical simulations are providing alternative to experimental methods in preliminary analysis of aerodynamic behavior for large wind turbines. Shortcomings inherent by experimental methods have popularized the three dimensional CFD methods. This paper, therefore, presents a numerical analysis for NREL 5MW wind turbine rotor using a single moving reference frame approach. ANSYS Fluent is employed to model airflow over the blade’s surfaces using Reynolds average Navier–Stokes equations. A steady-state incompressible pressure based solver is applied in form of absolute velocity formulation. Four turbulence models are used: $$k-\omega$$ SST, $$k-\epsilon$$ RNG, $$k-\epsilon$$ realizable and Spalart Allmaras to determine the aerodynamic torque. Mesh independence study and validation is also performed. In addition, the predicted flap-wise bending load and comparison of pressure distribution for the four turbulence models are evaluated at different sections of the blade. Due to absence of experimental data for employed blade model, the obtained aerodynamic torque was compared with other reliable numerical simulation results.

Enzymatic Hydrolysis of Lignocellulosic Biomasses via CFD and Experiments

The time evolution of the rheological properties of pretreated Arundo slurries has been estimated, during enzymatic hydrolysis for bioethanol production, by computational fluid dynamics simulations in conjunction with experimental tests on a laboratory scale anchor reactor with different solid concentrations (18.5 and 27.5% w/w) and stirring velocities (50–200 rpm). The simulations were carried out with Fluent 6.2 using the moving reference frame approach and the Herschel–Bulkley rheological model. Great care was taken in the development of the computational grid and in the solution of the numerical issues. The identification of the rheological parameters was successful and the results are consistent with other works published in the literature on similar systems. The next steps of this work will involve the use of these results to design new continuous reactors for enzymatic hydrolysis and their scale up to a pilot and industrial level.