Turbulent Kinetic Energy Contours Research Articles

Improvement of tube heat exchanger performance with perforated ring inserts, tube rotation and using nanofluids

Many engineering applications, such as waste heat recovery, air-conditioning and refrigeration systems, include heat exchangers. In this work, the performance of a double-tube heat exchanger with a rotating tube, perforated ring inserts and nanofluids as working fluids has been studied. After developing a 3D numerical model, verifying its discretization and validating it with experimental results, an optimal design for maximizing heat transfer while keeping a relatively low pressure drop was found (11 eight-holed rings with a 2.2 pitch ratio). Increasing the cold fluid Reynolds number to 4946 and the inner tube rotational speed to 500 rpm increased the heat transfer coefficient from around 7500 to 9500 W (m2 K)−1. Considering the nanofluids studied, the best performance was found with Cu nanoparticles, followed by Al2O3–Cu and Al2O3. With Cu nanoparticles at 3%, heat transfer coefficients above 12,100 W (m2 K)−1 were obtained, increasing heat exchanger effectiveness from 27 to 51%. Pressure drop levels increased up to 235 Pa, resulting in increasing pumping requirements by around 0.1 kJ kg−1. Hence, only very high flowrates would represent a problem when using the exchanger. Explanations for the underlying physical phenomena that cause the enhancement of heat transfer due to the rotational speed, the perforated rings and the nanofluids were provided. Turbulent kinetic energy contours, flow streamlines, and temperature contours were used to gain insight into the thermal and flow fields, identifying the mechanisms responsible for the enhancement of the heat exchanger effectiveness.

Potential need for vestibule structures in solar updraft tower

A solar updraft tower (SUT) is a power-generating structure that transforms solar energy into electricity through the kinetic energy of air rising due to solar-radiation-induced buoyancy. In traditional architecture, a vestibule is a small room that leads to the main room, and it separates the indoor and outdoor atmospheres, thereby reducing heat loss and improving the thermal performance of the main room. Herein, we propose a canopy-attached divider structure that can create a vestibule-like space and increase the overall thermo-fluid dynamic efficiency of SUTs. A computer simulation study was conducted for various divider geometries in terms of their locations and shapes to create diverse vestibules. The control parameters were the gap between the divider tip and the ground and the length along the radial direction, which determines the vestibule volume. SUT efficiency was analyzed using the velocity, temperature, and turbulence kinetic energy (TKE) contours obtained herein. The vestibule created by installing a divider with a gap of 0.06 m and a length of 4.6 m can increase the outlet velocity by up to 6.97%. The results of this study indicate the possibility of applying this thermo-fluid dynamic engineering technology used in other fields to SUTs.

Experimental and numerical simulation-based investigation for thermal characteristic of frustum roughened solar air heater

ABSTRACT This research paper aims to investigate the effect of frustum shape roughness geometry on the thermal characteristic (Nusselt no. and friction factor) of solar air heaters (SAH). The study includes experimental and numerical investigation of a solar air heater equipped with frustum roughened absorber plate under varying operating conditions. Frustum shape roughness element produced more disturbances and greater mixing of primary and secondary flow that resulted in greater augmentation in thermal characteristics of SAH. The investigation was conducted in varying Reynolds number range of 2500 -12,500. Dimensionless parameter for Frustrum shaped roughness is varied as relative frustum height (e/Dh) 0.013–0.054, relative frustum pitch (p/e) 8–14, Relative frustum height to base diameter (e/d1) 0.37–0.75 and relative frustum diametral ratio (d1/d2) 1–3. To save time and resources a three-dimensional numerical simulation was also performed. This simulation helped to visualize flow field behavior with the help of streamline, temperature, turbulence kinetic energy and pressure contours. Maximum performance for roughened system was obtained at optimum value of flow and geometric configuration within the range of investigated parameters. The geometric orientation of proposed roughness geometry produced tremendous rise in Nusselt number (Nu) with an acceptable rise in friction (f). Maximum enhancement in Nu for varying p/e, e/Dh, e/d1, and d1/d2 was, 4.58, 5.21, 6.62 and 6.09 times and that of friction was 5.59, 4.69, 4.92 and 4.66 times respectively over conventional smooth SAH.

Turbulent thermal-hydraulic characteristics in a spiral corrugated waste heat recovery heat exchanger with perforated multiple twisted tapes

Waste heat recovery technology can undoubtedly improve energy saving and reduce carbon emissions, as one of the key equipment, heat exchangers always determine the waste heat recovery efficiency. In this study, to improve the heat transfer potentiality of conventional plain tube heat exchangers, a synergistic thermal enhancement technology of a spiral corrugated tube (SCT) with multiple twisted tapes (TTs) was devised by taking liquid-gas heat exchanging as a typical waste heat recovery scenario. The impacts of the TTs numbers, transverse space ratios (S/D), and longitudinal perforation length ratios (L/D) on tubular turbulent heat transfer-fluid flow characteristics were numerically investigated, consisting of flow fields, temperature contours, local Nusselt number (Nu) distributions, vortex structures, and turbulent kinetic energy contours, as well as average Nu, friction factor (f), and overall thermal performance evaluation index (η). The findings proved that the fitting of multiple TTs into the SCT greatly homogenized the flow fields and temperature distributions, and increased the Nu and f, in which both of them also raised with the increase of the number of TTs. The η dropped and subsequently augmented as the quantity of TTs increased. Furthermore, perforations on the surface of the quadruple TTs could attenuate the f with a relative less reduction in the Nu, which caused higher η values than the ones without perforations. Notably, as demonstrated by the vortex structures, this could be ascribed to the fact that the perforations reduced excessive longitudinal vortex interactions in the mainstream regime without reducing the impingement to the thermal boundary layer too much. Both the Nu and f generally declined with rising S/D and L/D. Overall, by means of simple mounting perforations on the surface of the quadruple TTs, the maximum η could be further enhanced up to around 7.9% and a maximum η of 1.23 was obtained by the SCT with S/D = 0.152 and L/D = 0.348.

Correlations and numerical analysis of thermal-hydraulic performance of staggered mixed tube bundle composed of circular and drop-shaped tubes

Flow and heat transfer across six-row staggered mixed tube bundles composing of circular and drop-shaped tubes have been investigated numerically. The Reynolds number Re was within the range of 1.78 × 103–18.72 × 103. Six cases of the mixed tube bundle were discussed. The streamlines, velocity, turbulent kinetic energy, temperature, and static pressure contours for the studied cases were predicted using Ansys Fluent software package. The results of the mixed tube bundles were compared with those of the circular and drop-shaped ones. The best thermal performance was obtained for case IV (circular tubes in the 1st, 3rd, 5th rows, and drop-shaped tubes in the 2nd, 4th, 6th rows). However, it was found that case VII (drop-shaped tubes in the 1st, 2nd, 4th, 6th rows, and circular tubes in the 3rd, 4th rows) has the best hydraulic performance compared to the other cases of circular and mixed tube bundles. Besides, the average Nusselt number Nu¯, friction factor f, and efficiency ε were observed to be positively correlated to the Reynolds number. As the Re increased, both Nu¯ and ε increased, while f decreased. Results showed that the maximum values of the thermal-hydraulic performance were achieved for case IV at Re = 1.78 × 103 and case VII at Re>1.78 × 103, which were about 14.55% and (2.08–4.49)%, respectively, higher than those obtained for the drop-shaped tube bundle. Finally, generalized correlations of Nu¯, f, and ε (in terms of Re) were developed, offering a useful reference for the design of such heat exchangers.

Analysis of the scaling mechanism and characteristics of a double-defects screen based on data from Hafaya oilfield

Corrosion defects of screen occurred frequently in sand control process due to the influence of formation factors. The main purpose of this study was to analyze screen scaling based on field data with CFD technology under different sizes, quantities and distribution modes of corrosion defects. A full presentation of turbulent Kinetic Energy contours, wall shear stress contours, fluid velocity and temperature on the screen surface are presented and discussed in the process of scaling. The distribution characteristics of CaCO3 in the scaling model were used to characterize the scaling characteristics. Furthermore, prediction model of scaling thickness was established to systematically evaluate the results. The conclusion of numerical analysis showed that with other conditions unchanged, the scale of radial distribution is larger than that of axial distribution. More over, the larger the defect width and distance, the less obvious scaling. However, the defect depth indicated the opposite results, which meant that the size factor has the greatest influence on scaling. Keeping the environmental conditions changed, velocity and temperature showed obvious influence on particle scaling. It reveals that the velocity of produced liquid has a great influence on the defect screen with different distribution modes.When the size condition of the defect were kept remained, the scaling amount of screen increases obviously with the increase of velocity. The influence of temperature on the two different distribution patterns of defects was not obvious. With the increased of the temperature, the amount of scaling in the pipe also increased similarly. Considering the results, this research could be used as basis to offer safe operating guidelines to reduce the scaling in the screen due to corrosion defects in oil production. To mitigate the impact of this factor on production, scaling can be addressed by reasonably increasing the velocity of the produced liquid and lowering the temperature with the defects exist.

Dependence of wall jet phenomenology on inlet conditions and near-field flow development

In this paper, the three-dimensional turbulent wall jet flow is investigated for three different developing initial velocity profiles. The developing initial velocity profiles at the nozzle exit are generated by three different lengths (, 50 and 90) of the square nozzle . The velocity profiles at the nozzle exit are measured with the single probe hot-wire anemometer. The Reynolds number based on the bulk mean velocity and nozzle height is 25,000 for all the cases. The measured velocity profiles at the nozzle exit are used as the inlet conditions for the numerical simulations. The results show that the initial velocity profile affects the flow field of the wall jet in near and far-field regions. It is found that the contours of streamwise velocity and turbulent kinetic energy exhibit the effect of initial conditions in the near field. The Reynolds shear stress component dominates in the vertical jet centreline plane, and it increases with a decrease in the nozzle length. The Reynolds shear stress component dominates in the lateral plane, and also exhibit the dependency on initial conditions.

Experiment and Simulation of One Deep Sewage Discharge Type: Transport of Low‐Salinity Sediment‐Laden Flow Discharged

AbstractDeep sewage discharge leads to inestimable damage to the ambient water (lakes, oceans and reservoirs), which has caused widespread social concern. In the current paper, a three‐dimensional (3D) buoyancy plume model for deep sewage discharge was developed. It simulates sediment‐laden flow with the effects of temperature and salinity differences. Taking the turbulent diffusion coefficient of salinity (αsal) as the calibration parameter, a comparison between the RNG k‐ε and the standard k‐ε models was performed. The proposed model was verified well and agreement with experiment, which proved that the RNG model with the αsal value of 0.4 was the optimal calibration. Then the model was applied to quantify the behavior of the buoyant plume in the ambient fluid (salt water) with respect to different contours of turbulent kinetic energy (k), temperature, salinity and sediment. The dimensionless centerline trajectory positions and boundary positions of them were determined. The results indicated that the discharge of low‐salinity sediment‐bearing water influenced the deep ambient water spatially, both near the free surface and in the vertical plane. Different diffusion and spreading shapes (butterfly, Ginkgo biloba, bean) can be observed on the surface. Accurately evaluating the impact of deep discharge on ambient water has great significance for maintaining healthy and sustainable environments in offshore areas, deep lakes and reservoirs.

Thermodynamic investigation on solar air heater having roughness as multiple broken arc and circular protrusion

This study looked at the effectiveness of a solar air heater for heating air that has multiple ribs (broken arc shaped) and an arc-shaped circular protrusion on the rear side of the solar air heater absorber plate. Simulations were done on the commercial code FLUENT (v14.0) using the RNG k-ξ model at a uniform heat flux of 1000 W/m2. The relative roughness pitch of the rib are ranging from 10 to 30, broken arc rib has height of 1 mm, the gap between the broken arc and circular protrusion is 2.5 mm, the distance between two broken arc ribs has been kept as 20 mm, and circular protrusion has diameter of 0.8 mm In present study the maximum hydraulic thermal performance (THP = 3.31) was observed at Re = 20,000 where g/e = 0.8, protrusion diameter d = 0.6 mm, distance between the roughness p = 30. To better understand fluid flow physics, velocity pathlines, temperature contours and turbulent kinetic energy contours have been plotted. The post-CFD result shows the design of roughness is beneficial in achieving desired performance of solar air heater. The presence of gaps and protrusions creates the required turbulence in the duct that improve the thermal performance of solar air heater with minimum penalty of frictional pressure drop.

Numerical simulations over a three body launch vehicle for incompressible flows

In the present work, three dimensional numerical simulations over a launch vehicle at 70 m/s are performed for 3 scale models. The vehicle has a cylindrical core body and two strap on boosters. The scaled models chosen so that they represent a wind tunnel blockage ratio of 3%, 4% and 5% respectively. Simulations are performed using commercial CFD software Ansys Fluent. Three dimensional structured mesh is generated using ICEMCFD software. The solver depends on finite volume technique, and SIMPLE calculation is utilized to address the couple continuity and energy conditions. K-w SST model is utilized for disturbance demonstration. The computed flow field is analyzed in terms of velocity, pressure and turbulent kinetic energy contours. Surface pressure acquired from the three simulation (relating to every blockage ratio) arrangements in balance plane is compared to understand the impact of blockage ratio on the stream field and drag coefficients. As the blockage is increased, it was observed that maximum velocity is increasing. Lowest blockage found to give highest drag coefficient.

Effects of pile-cap elevation on scour and turbulence around a complex bridge pier

ABSTRACT In this study, the local scour and the associated flow hydrodynamics around a complex pier with rectangular pile-cap at three different pile-cap elevations are investigated. The pile-cap elevations were selected with respect to the initial sand bed, such that the pile-cap was unexposed (case I), partially exposed (case II), and fully exposed (case III) to the flow. The experiments were performed in a recirculating flume under clear-water scour conditions, and the instantaneous flow velocity was obtained at different vertical planes using the particle image velocimetry (PIV) technique. The partially exposed pile-cap case showed the maximum obtained scour-depth (MSD). The reason behind the MSD occurrence in case II was enunciated through the analysis of turbulent flow field which showed that as the pile-cap got exposed to the flow, it dominantly affected the generation of vortices from the pile-cap corners responsible for the higher scour depth. The effect of the pile-cap on the flow field was prominently seen in case III through the mean velocities, vorticity, Reynolds shear stresses and turbulent kinetic energy contours, but since the pile-cap was away from the bed, the pile-cap corners did not show any direct effect on the scour.

Effects of tip clearance size on vortical structures and turbulence statistics in tip-leakage flows: A direct numerical simulation study

Direct numerical simulations of the tip-leakage flow, generated by a gap between a straight National Advisory Committee for Aeronautics 0012 hydrofoil and the end wall of a channel, have been performed to investigate the effects of tip clearance size on vortical structures and turbulence statistics. The tip-leakage vortex, tip separation vortex, and induced vortex are the predominant vortical structures in tip-leakage flow for a relatively large gap (3.33%Ca), while the reverse flow vortex dominates the tip clearance region for smaller gaps (1.67%Ca), where Ca is the truncated chord length of the hydrofoil. Detailed analysis of turbulence statistics reveals that the tip-leakage vortex is caused by the rollup of the tip-leakage jet, while the spanwise inflow interacting with the sidewall of the hydrofoil leads to the formation of a reverse flow vortex. The turbulent kinetic energy contours show an arc-shaped distribution on the suction side of the hydrofoil, but their locations are significantly affected by the tip clearance size. In addition, the investigation of tip-leakage loss indicates that increasing the size of the tip clearance can reduce the tip-leakage loss across the hydrofoil. This can be attributed to the dominant vortical structures in the tip-leakage flow.

An experimental investigation of a rotationally oscillating cylinder

The flow patterns of the wake region of a rotationally oscillating cylinder were investigated experimentally by using the Particle Image Velocimetry (PIV) technique and dye visualization. The experiments were conducted at Reynolds number Re = 1000 and different values of oscillation amplitude (θA = 60°, 120°, 180°) and frequency ratio (FR = 0.8, 1.7, 3.3, 6.7). Dye visualizations, instantaneous vorticity contours, time-averaged streamlines, vorticity, streamwise and crossflow velocity contours, Reynolds stress correlations, turbulent kinetic energy (<TKE>) and autospectral density contours were analysed. For FR = 0.8, the vortices formation behind the cylinder wake disappeared and the only saddle point formation was observed at θA = 120° and θA = 180°. The maximum and minimum shear stress <u′v′> were obtained at FR = 0.8, θA = 180° and FR = 3.3, θA = 120°, respectively. The turbulent kinetic energy decreased with the increase in the frequency ratio at θA = 180°, and it has been observed that the vortex shedding weakens the interaction between the upper and lower vortices of the cylinder. The maximum decreasing in the drag coefficient of the stationary cylinder was by around 46% at FR = 6.7 θA = 120°. It is concluded that the rotationally oscillating cylinder has a significant effect on the cylinder wake region and changes the wake flow structures and vortex shedding patterns.

Reynolds Number Effect on the Flow Demeanorin a Vertical Circular Free Turbulent Jet with Cross Flow

This paper deals with studying numerically two circular turbulent jets impinging on a flat surface with a low velocity cross flow by using ANSYS CFX 16.2, with the aim of proving the effect ofReynolds number on the flow demeanor in a vertical circular free turbulent jet with cross flow. Five turbulence models of the RANS (Reynolds Averaged Navier–Stokes) approach were tested and the k -ω SST model was chosen to validate CFD results with the experimental data. Average velocity profiles, velocity and turbulent kinetic energy contours and streamlines are presented for four case configurations. In the first three cases, the following parameters have been varied: Reynolds number at the level of the two jets ( ), wind velocity at the level of the cross-flow ( ), and the distance between the two jets (S = 45mm, 90mm and 135mm). In the last case, a new configuration of the phenomenon not yet studied so far was treated, where horizontal cross-flows were introduced from both sides in order to simulate gusts of wind disrupting a VSTOL aircraft which tries to operate close to the ground. This case was carried out for Reynolds number based on the crossflow of 4 104, 10 104 and 20 104 .The numerical results obtained show that the deflection of the jets is minimal when the Reynolds number at the level of the jets is greater than that of the cross-flow. The increase of Reynolds number at the level of the cross-flow reveals a significant deviation of the two jets with an intensity which always remains less for the second jet. As for the space parameter between the two jets, it turns out that the fact of further spacing the two jets makes the first jet even more vulnerable and leads to a greater deflection. Finally, the simulation of the wind gusts from the front and the back caused a zone of turbulence which resulted from a form of "interlacing" of the two jets under the effect of the transverse current imposed by the two sides.

Optimization of critical angle, distance and flow rate of secondary fuel injection in DI diesel engine using computational fluid dynamics

This study presents the optimization of the intake manifold and the optimized flow rate of the acetylene gas which acts as a low reactivity fuel to achieve the superior performance and emission characteristics used in the Reactivity controlled compression ignition (RCCI) engine. Intake manifold is one of the engine components which are an important factor in determining the quality of combustion. A very recent evolution of the RCCI engine using the low temperature combustion technique requires a low reactivity fuel which is injected through the secondary fuel injector. The secondary fuel injector must be designed and optimized to allow the acetylene gas to maximize the engine performance and the amount of acetylene gas in liters per minute required for better combustion. If the secondary fuel injector is mounted apart from the critical point, then the performance of the RCCI engine may be poor and also if the acetylene gas is not supplied properly, there is a risk of poor combustion and also if the acetylene gas is supplied excessively, there is a risk of knocking along with the backfire due to the excess fuel charge accumulation during the combustion process. Physical testing of the secondary fuel injector in the intake manifold with different angles, distance and flow rate of supply of acetylene gas is time and cost consuming process. To mitigate this issue optimization is done through computational fluid dynamics principles comes in handy to minimize time and money. In our study, ANSYS-FLUENT software is used for simulation purposes. Optimization of acetylene gas injector distance is carried out by analyzing the pressure contours at the entrance of the combustion chamber. The optimized flow rate of acetylene gas and the injector inclination is found by analyzing the flow contours of turbulent kinetic energy and turbulent dissipation rate.

Improved detached-eddy simulation of the turbulent unsteady flow past a square cylinder

The separated turbulent flow past a square cylinder mounted centrally inside a plane channel has been numerically investigated in this work. A three-dimensional paradigmatic calculation was carried out to capture the essence of flow parameters through different detached-eddy simulations (DESs). The predictions were performed based on the original DES, delayed DES, and one modified DES (MDES). First, MDES closure was validated by comparing the simulation results with the experimental data of separated flow through a U-turn duct, thereafter commencing the predictions of the flow past a square cylinder. The comparisons between the numerical and available experimental results show that the MDES has better capability than the DES to capture the characteristics of global variables including the Strouhal number, mean drag and lift coefficients, and their standard deviations for the square cylinder case. Furthermore, a detailed quantitative comparison in terms of the time-averaged velocity profiles at specified locations reveals that MDES could be more reasonable and has better fidelity than the other two models. A good match among the contours of eddy viscosity, Q-criterion, and turbulent kinetic energy shows that MDES has correctly reproduced the turbulent production in the wake flow. The main significance of this study is that it demonstrates the potential of a modified DES closure to investigate the unsteady dynamics in the wake flow past a square cylinder and expected to make sense for other wake flows of engineering interest.

Thermal design evaluation of ribbed/grooved tubes: An entropy and exergy approach

The smooth circular tubes are typically used in air-cooled heat exchangers systems. In literature, various research toward improving the hydraulic/thermal performance by changing the tubes' inner surface topology is found. In the current work, fluid friction and heat transfer characteristics of air-cooled tube heat exchangers with installed ribs and grooves have been numerically compared. Initially, the numerically calculated data of the ribbed tubes are validated /compared to the performance results in the literature. Performance evaluation criteria (PEC), entropy and exergy are numerically investigated for a tube with a group of ribs and grooves over the range of Reynolds number Re = 6700–20,000. Rib radius (r), number of ribs in the same group (Ng), the distance between two adjacent ribs (SL), and pitch between two adjacent groups (p) are the ribs parameters selected to study their effects on flow and heat transfer criteria. Also, the same evaluation criteria are performed on grooved tube with optimal parameters to make a comparison between results. Moreover, streamline patterns and temperature/pressure/velocity/turbulence kinetic energy contours are visually introduced to explicate the physics of heat transfer and pressure drop phenomena and to assess the flow structures inside different ribbed/grooved tubes. For the tubes with high-performance evaluation criteria (PEC), lower and higher entropy and exergy efficiency are determined. Recapitulation results from the technical comparison supported the use of grooved-tubes instead of ribbed-tubes. This is mainly due to lower flow irreversibility accompanied by higher PEC and exergy efficiency than those of ribbed tubes at the same flow condition.

Investigation of airflow at different activity conditions in a realistic model of human upper respiratory tract

In the present study, the turbulent flows inside a realistic model of the upper respiratory tract were investigated numerically and experimentally. The airway model included the geometrical details of the oral cavity to the end of the trachea that was based on a series of CT-scan images. The topological data of the respiratory tract were used for generating the computational model as well as the 3D-printed model that was used in the experimental pressure drop measurement. Different airflow rates of 30, 45, and 60 L/min, which correspond to the light, semi-light, and heavy activity breathing conditions, were investigated numerically using turbulence and transition models, as well as experimentally. Simulation results for airflow properties, including velocity vectors, pressure drops, streamlines, eddy viscosity, and turbulent kinetic energy contours in the oral-trachea airway model, were presented. The simulated pressure drop was compared with the experimental data, and reasonable agreement was found. The obtained results showed that the maximum pressure drop occurs in the narrowest part of the larynx region. A comparison between the numerical results and experimental data showed that the transition () SST model predicts higher pressure losses, especially at higher breathing rates. Formations of the secondary flows in the oropharynx and trachea regions were also observed. In addition, the simulation results showed that in the trachea region, the secondary flow structures dissipated faster for the flow rate of 60 L/min compared to the lower breathing rates of 30 and 45 L/min.

On the Performance of Small-Scale Horizontal Axis Tidal Current Turbines. Part 1: One Single Turbine

The blade number of a current tidal turbine is one of the essential parameters to increase the stability, performance and efficiency for converting tidal current energy into rotational energy to generate electricity. This research attempts to investigate the effect of blade number on the performance of a small-scale horizontal tidal current turbine in the case of torque, thrust coefficient and power coefficient. Towards this end and according to the blade element momentum theory, three different turbines, i.e., two, three and four-bladed, were modeled using Solidworks software based on S-814 airfoil and then exported to the ANSYS-FLUENT for computational flow dynamics (CFD) analysis. SST-K-ω turbulence model was used to predict the turbulence behavior and several simulations were conducted at 2 ≤ tip speed ratio ≤ 7. Pressure contours, turbulence kinetic energy contours, cut-in-speed-curves, and streamlines around the blades and rotors were extracted and compared to provide an ability for a deep discussion on the turbine performance. The results show that in the case of obtainable power, the optimal value of tip speed ratio is around 5, so that the maximum power was achieved for the four-bladed turbine. Out of optimal condition, higher blade number and lower blade number turbines should be used at less than and greater than the optimal values of tip speed ratio, respectively. The results of simulations for the three-bladed turbine were validated against the experimental data with good agreement.

Experimental and numerical investigations for turbulent air flow characteristics of circular orifice plate

The present work describes the airflow characteristics upstream and downstream of the circular orifice numerically using the standard k-ε model and RSM and experimentally employing hot-wire and Pitot tube devices to measure the flow velocities through a tube. An expectation has to bear in mind; the RSM performed well and predicted results in a good level of agreement against the experimental measurements found in preceding studies and the present experimental data as well. In terms of flow physics point of view, velocity and turbulent kinetic energy distribution are presented. Moreover, turbulent viscosity, Reynolds stresses (u2, v2, w2) are also considered. Furthermore, the contours of velocity, static pressure and turbulent kinetic energy are presented beside the wall shear stress and y+ profiles are illustrated to show the flow physics as well as to compare the results of two different turbulence models considered in this study employing Reynolds of 30000 and the ratio of orifice diameter to the pipe diameter of 0.5.