computational fluid dynamics

With the changing patterns of energy consumption and the emergence of economic and environmental issues, renewable energy production has received a lot of attention all over the world. Micro-hydropower plants that utilize pumps as turbine (PAT) instead of traditional turbines offer unique advantages such as low construction and maintenance costs, and short commissioning time. In the present study, the design and simulation of a centrifugal PAT were performed using CFturbo and CFX software. The governing equations were discretized using the finite volume method, and the k-ω SST turbulence model was employed for numerical analysis. The performance curves of simulated PAT show acceptable agreement with experimental results. Since pumps are not designed for reverse operation and lack equipment to guide fluid flow from the volute to the impeller, significant losses occur, particularly under off-design operating conditions. In order to improve the PAT performance, diffusers equipped with stay blades were designed for implementation in the space between the impeller and the volute, and the effect of the number of stay blades on operating range was numerically investigated. Results indicate that the PAT equipped with a 10-blade diffuser exhibits more uniform turbulent kinetic energy distribution and provides a wider operating range with high efficiency. Besides, the PAT efficiency at the design point has increased by 2.7%.

The current research has studied the piezoelectric blade sensor from different views in order to control the oscillations of the circular cylinder present upstream of the piezoelectric blade and to control the fluctuating fluid flow around the blade using the force on the piezoelectric blade. The desired arrangement of a piezoelectric blade is placed downstream of a circular cylinder and with the help of a certain limit of blade oscillations, the hardness coefficient of the cylinder spring is applied from 65 (N/M) in normal condition to 100 (N/M) in the necessary condition. The controller as well as in other cases, the damping rate increases from zero to 0.02 (Nm/S) and in this way, the oscillations of the cylinder are controlled. In the same way, by controlling the oscillations of the cylinder, its effect on the oscillations of the blade, which is located downstream, has been investigated under the title of feedback effects. By controlling the feedback of the force on the piezoelectric blade in a closed loop, it is possible to monitor the displacement of the tip of the blade and the force on the piezoelectric blade. In these studies, it has been determined that in the case where the specific limit of the controller is 0.7 mm of the oscillations of the piezoelectric blade tip, due to the earlier application of the controller compared to the specific limit of 1 and 2 mm of the oscillations of the blade tip, the oscillations of the cylinder are Also, by comparing the state where the controller is included in the circuit compared to the state without the controller, it is clear that the oscillations of the blade and cylinder have been controlled to some extent.

In modern wind turbine design, two significant challenges arise: achieving optimal aerodynamic performance while minimizing acoustic noise emissions. However, the extensive numerical computations required for accurate evaluation often hinder the implementation of multi-objective optimization strategies. This paper introduces an innovative approach to address this issue, leveraging a combination of neural network-based reduced order modeling and a multi-objective genetic algorithm. This methodology aims to optimize the aerodynamic and aero-acoustic characteristics of an S8xx-series airfoil, including the trailing edge serration geometry. Utilizing Class-Shape Transformation to parameterize various serrated airfoil geometries, the method minimizes the need for costly computational fluid dynamics (CFD) simulations. Instead, a feed-forward neural network (NN) is trained with a minimal dataset to predict airfoil behavior within a specified range. Comparisons between CFD results and NN predictions validate the accuracy of the neural network. Significantly, this approach substantially reduces optimization time by approximately 95%, maintaining high levels of accuracy. In conducting multi-objective optimization for both the airfoil and serration shapes, the study demonstrates notable improvements: a 5 to 7% enhancement in aerodynamic performance alongside a simultaneous 1-4% reduction in noise compared to benchmark airfoils. Then, in the second step, experimental methodology is employed to investigate the aeroacoustic attributes of a small horizontal-axis wind turbine with optimized blades. Conducted within a semi-anechoic chamber, this investigation meticulously positions both original and optimized geometry models to measure sound pressure levels (SPL) across various rotational speeds and positions. The results reveal subtle enhancements in aerodynamic performance with the optimized serrated blade configuration, accompanied by a remarkable reduction in noise levels across the frequency spectrum, culminating in an impressive overall sound pressure reduction of approximately 10 dB. Additionally, intriguing observations highlight the impact of turbine rotational speed on noise production, particularly in the downstream domain. Notably, the noise emission reduction for the serrated optimized blade is more dispersed in the plane of rotation compared to the original blade, which exhibited nearly uniform noise distribution. Overall, these findings offer valuable insights into the intricate interplay between aerodynamics and aeroacoustics in the context of small wind turbines with optimized blades.

Blood flow characteristics have a considerable impact on drug uptake from drug-eluting stents. For this reason, in this study, the effect of pulsatile blood flow induced by heartbeats on hemodynamics and drug transfer from drug-eluting stents has been investigated using computational fluid dynamics. Previous studies have investigated the effect of this feature on renal vessels; However, this issue has not been investigated in the case of coronary arteries. For this purpose, the blood flow and drug transport in the lumen and tissue of a stented right coronary artery have been simulated in an unsteady and non-Newtonian manner. To analyze the impact of pulsatile flow waveform, three different pulsatile flows including a physiological waveform in the human right coronary artery, a general physiological waveform in the arteries of the human body, and a simple sinusoidal waveform were imposed. Furthermore, the results were compared for three Womersley numbers and two Reynolds numbers. The results indicate that the blood flow waveforms and their frequency (Womersley number) have a negligible effect on hemodynamics and drug transfer parameters. However, the impact of Reynolds number is significant. The results also show that the impact of Newtonian or non-Newtonian blood viscosity on hemodynamics and drug transfer is negligible. Therefore, assuming blood as a Newtonian fluid in these simulations could be accurate.

Heat exchangers are widely used in various industries, including power plants, solar cells, refineries, and automobiles. One of the simplest types of heat exchangers used in the industry is the double-pipe heat exchanger. In the present study, nanofluid flow in a double-pipe heat exchanger, with a square inner pipe and a circular outer pipe (sc), is simulated and investigated using computational fluid dynamics under constant heat flux and within the range of laminar and turbulent flow regimes. To verify the accuracy of the numerical study in both laminar and turbulent flows, the numerical calculation results for water flow with forced convection were compared with reference results. The results showed that with an increase in the Reynolds number, particularly in the turbulent flow regime, the Nusselt number in nanofluid flow increased more than in water flow. For instance, for aluminum oxide nanofluid flow with a Reynolds number of 500, the Nusselt number increases by nearly 5% more than water flow, and for a Reynolds number of 20000, this Nusselt number increase is close to 20% more. To investigate the impact of nanoparticle type on heat transfer and pressure drop, three types of nanoparticles were considered. The results indicated that the use of nanoparticles had a slight effect on the friction coefficient while significantly enhancing heat transfer.

In this research, computational fluid dynamics method was used to investigate the effect of geometrical parameters of rectangular spiral channels on heat transfer coefficient. Two artificial neural networks including perceptron (MLP) and radial basis function (RBF) models were used to model the heat transfer in helical channels. The model inputs included the Reynolds number and geometric parameters of the channel, and output was the Nusselt number. 135 data were generated by Computational Fluid Dynamics (CFD) simulation and after validation were used for training and evaluation of neural network models. The results of the research showed that the accuracy of MLP was slightly higher than RBF, however, both models were acceptable. Due to the high and acceptable accuracy of these two models, they can be well used in future research and applications. In this research, the main innovation is comparing two different methods for modeling the heat exchanger with a rectangular helical channel. This research shows that the use of perceptron neural network and radial basis function can both be effective in improving the performance and efficiency of the heat exchanger. This research can be used as a guide to choose the appropriate method for modeling heat exchangers and help to improve technologies related to this field.

In this research, the behavior of air flow, temperature, and humidity changes inside a greenhouse will be modeled using numerical simulation. To increase the humidity of the air flowing inside the greenhouse, water is sprayed into the air with two amounts of mass flow rate, through the greenhouse using three different methods. In the first method, two moisturized pads are used. In the second method, two water sprays at specific distances and a height of 3m from the greenhouse floor are used. In the third method, twenty-seven water droplet sprays in different locations are used. On the other side of the greenhouse hall, there are four fans with negative pressure, establishing fresh air flow inside the hall. The turbulence modeling approach was used to model the effects of turbulence in the flow field. After validating the numerical results, the outcome model has been used to study the flow behavior and the effect of the latent energy of water in greenhouse ventilation and relative humidity. By examining fourteen conditions of water droplet injection inside the greenhouse, the most suitable condition contains 50pa back pressure, 27 sprays, and a mass flow rate of droplet injection of 0.04 kg/s. On the other hand, if the mentioned plans are examined with the criterion of temperature changes and suitable environmental conditions. It can be seen that the outlet pressure of 100pa and mass flow rate of 0.08kg/s for water droplet injection in moisturized pad configuration, will be the best plan for the growth of plants such as Gladiolus in the greenhouse environment.

Today, the production of fresh water using reverse osmosis method is the affordable options in many countries. One of the problems of this method is the reduction of the amount of permeate water due to increase of salinity and temperature of raw water throughout the year. In this article, a method for redesigning the hydraulic turbocharger rotor has been discussed so that the amount of permeate water can be kept relatively constant without. For this purpose, firstly, the performance of a working plant was investigated, then using computational fluid dynamics and similarity relations in turbomachinery, two new rotors were designed and manufactured for the existing turbocharger to be used in two modes of high and low membrane pressure. To verify the validity, the design parameters have been compared with the test data. The results show that despite the change in the membrane, replacing new rotors The new rotor design has made the water production unchanged. The efficiency has also increased in one of the cases more than 4% and energy recovery about 2%. So, it can be concluded that this method can be used in seasons when the pressure change of the membranes is noticeably higher or lower than the initial design pressure.

burn conditions and stable combustion. Therefore, in the current research, the effect of rotation ratio, equivalence ratio and ignition time on pressure, temperature, engine output power and pollutant emissions of a pre-chambered gas engine was investigated using computational fluid dynamics. This research generally consists of three parts; in the first part, the combustion chamber geometry of an engine equipped with pre-chamber technology is drawn and gridded. In the second step, dynamic motion is given to the combustion chamber and the chamber is simulated in motoring mode (without combustion). In the third step, the combustion process inside the chamber was analyzed using Fluent software. This analysis, which included methods for solving the problem of computational network dynamics and the transfer of components due to combustion, provides the profiles of temperature and pressure, fuel consumption, output work, and other functional characteristics of the engine. Analysis of the effect of air fuel ratio showed that the best operating equivalence ratio at full load is 2, which is the equivalence ratio of the base engine. Also, the results showed that the ignition time of 12 and 15 degrees before the top dead point shows acceptable operating conditions. Ignition timing 12 showed lower NOx production and higher exhaust gas temperature compared to ignition timing 15.

In this paper, using computational fluid dynamics, the air flow pattern and temperature distribution for a high-density data center is presented. The Air-pack software is employed to evaluate the performance of the cooling system within the data center. A high-density data center with a total power density of 227.2 kW is considered. The arrangement considered for the data center is a cold/hot aisle layout and also two computer room air conditioning (CRAC) units are employed to produce cold air flow. A three-dimensional analysis of cold/hot air flow within the data center is provided and high temperature and hot air re-circulation areas are predicted. The results of this research show that in the entrance of the higher thermal density rack servers, there are areas with a temperature of 32.7℃ , which exceeds the permissible limit determined by the ASHRAE standard. But the temperature distribution of lower thermal density rack servers is completely consistent with the ASHRAE temperature range. Also, the hot exhaust air is recirculating into cold aisles and mixing with the supplied cold air.  This model could be used to evaluate the air flow and thermal mapping in order to design a new data centers or to optimize existing data centers in terms of reducing the problems in data center cooling, including hot air return and cold air bypass.