Flow Aerodynamic Characteristics Research Articles

Numerical Aerodynamic and Aeroacoustic Analysis of Toroidal Propeller Designs

Drones have a major drawback which prevents them from being used extensively - the excessive noise they produce. This article presents an optimization process of aerodynamic noise reduction for a novel design called the Toroidal Propeller, which consists of two blades looping joined in a manner where the end of one blade arches back into the other, has been designed by the Aerospace Propulsion Systems (APSs) research team at School of Mechanical Engineering, Hanoi University of Science and Technology. In addition, four toroidal propellers with different curved shapes (pitch) and Number of Blades (NOB) are considered. The goal of this research is to evaluate the effects of modifying the geometry design of the Toroidal Propeller on the intensity of blade tip vortex and aerodynamic flow characteristics passing through the blade. The ultimate goal is to decrease blade tip vortex and turbulence produced by the blade, which can help estimate the sound pressure level and minimize it without causing significant performance losses. Based on the outcome results, the models of the four geometry studies are compared in terms of Acoustic Power Level (APL), Surface Acoustic Power Level (SAPL), Thrust, Torque, and Power. In general, the propeller model with NOB of 3 provides the most optimal efficiency in terms of both Thrust and APL. At the output cross-section, the APL dropped from nearly 139 dB to 121 dB, while thrust increased from almost 6.2N to 8.7N compared to the first version of the Toroidal Propeller model.

Numerical and experimental investigation for helical savonius rotor performance improvement using novel blade shapes

Wind energy is extensively invested as a renewable and clean energy source. Savonius wind rotor, as an energy converter, has the merit of being appropriate for specific applications. The current paper centers on the performance enhancement of a helical Savonius wind rotor through the blade shape modification. The basic objective is to assess and compare, numerically and experimentally, the performance of two rotors with novel blade shapes named delta bladed and two-stage delta bladed shapes in relation to a helical Savonius rotor. Numerical study was conducted using Ansys Fluent software. 3-D unsteady simulations were carried out through the use of the SST k-ω turbulence model based on the finite volume method solver. Aerodynamic flow and performance characteristics were investigated. Static and dynamic experimental tests were undertaken on a wind tunnel. An improvement in Cp by 22.58 % and 29.5 % for the two-stage delta bladed rotor and 19.35 % and 16.4 % for the delta bladed rotor over the helical Savonius rotor was recorded, respectively, numerically and experimentally. In addition, the self-starting ability as well as the aerodynamic flow characteristics of the helical rotor were enhanced with the novel blade shapes.

Physical simulation of aerodynamic flow characteristics in a vertical diffuser with air supply through different pipe configurations

RELEVANCE. Vertical cone diffusers are used in various technical applications: heat exchangers, gas cleaning units, boilers, industrial furnaces, dryers, ventilation devices, nozzle systems and others. For their efficient operation, it is necessary to ensure a uniform supply of the working medium to the device, which is determined by the characteristics of the flow in thediffuser. Thus, the study of the aerodynamics of technological devices with conical diffusers is an urgent task for gas-dynamic improvement and the search for ways to control flow characteristics. THE PURPOSE. To establish the evolution of the velocity field along the height of the cylindrical part of the diffuser for different configurations of the supply tubes, and also to determine the magnitude of the change in the intensity of turbulence along the height of the diffuser under different initial conditions based on experimental data on the instantaneous values of the air flow velocity. METHODS. Measurement of instantaneous values of air flow velocity is carried out using a constant temperature hot-wire anemometer. The article provides data on velocity fields and turbulence intensity along the height and along the diameter of the cylindrical part of the diffuser when air is supplied through tubes of different configurations. Feed tubes with cross sections in the form of a circle, a square and an equilateral triangle were used. RESULTS. The article provides a detailed description of the experimental stand (including key geometric dimensions), instrumentation and measurement system, and data processing techniques. The ranges of changes in the initial conditions for the experiments are presented. A comparison of the aeromechanical characteristics of flows in a vertical diffuser when air issupplied through different tube configurations is carried out. CONCLUSION. It is shown that in the diffuser there is a drop in the average velocity upstream, which is typical for all configurations of the supply tubes. It has been established that profiled tubes influence the shape of the velocity field. It was found that the values of turbulence intensity vary from 0.05 to 0.39 (the highest values were typical when air was supplied through profiled tubes). It is shown that the intensity of turbulence has its maximum values at a height of 300-350 mm, which is typical for all investigated tube configurations.

Investigation on the Aerodynamic Performance of High-Pressure Cylinders under the Mode of Regulating Steam Supply with an Intermedium-Pressure Adjustment Valve

In order to investigate the operational performance of the high-pressure (HP) cylinder towards a 300 MW boiler unit, the three-dimensional calculation method was applied to simulate the aerodynamic flow characteristics of the last five stage cylinder blades, including limiting streamline, isentropic efficiency along the blade height, and relative work amounts. Simulation results show that with the back pressure controlled at 3.4 MPa and the inlet steam flow decreasing to a certain extent, the flow state of the last three stage blades begins to deteriorate. When the back pressure continues to drop, the flow state becomes unstable at the blade root and the blade tip on the suction surface of the rotor blade, while the flow state is stable on the pressure surface of the rotor blade and the surface of the stationary blade. If the flow rate decreases, the flow separation area on the suction surface of the moving blade decreases, and the flow performance can be improved. With the decrease in the boiler load, the total-total isentropic efficiency for the last three stage blades of the HP cylinder gradually decreases. In addition, the isentropic efficiency at the blade root and blade tip is lower than that for the blade body, which is closely related to the flow separation phenomenon of the last three stages of moving blades at the root and tip. In the working condition of the intermedium-pressure adjustment valve, since the temperature variation is within a limited range, operational safety can be guaranteed under the design blade frequency and strength. This paper provides the upper and lower limits of the exhaust gas pressure for the HP cylinder under the intermedium-pressure adjustment valve participation mode concerning various working conditions as well as corresponding constraints. This is conducive to guiding the design and safe operation of the intermedium-pressure adjustment valve. Through adjusting the intermedium-pressure adjustment valve, a specific supply capacity of the unit can also be satisfied at the lower load, which is beneficial to the deep peak regulation of the unit.

Dynamic flight load measurements with MEMS pressure sensors

The determination of structural loads plays an important role in the certification process of new aircraft. Strain gauges are usually used to measure and monitor the structural loads encountered during the flight test program. However, a time-consuming wiring and calibration process is required to determine the forces and moments from the measured strains. Sensors based on MEMS provide an alternative way to determine loads from the measured aerodynamic pressure distribution around the structural component. Flight tests were performed with a research glider aircraft to investigate the flight loads determined with the strain based and the pressure based measurement technology. A wing glove equipped with 64 MEMS pressure sensors was developed for measuring the pressure distribution around a selected wing section. The wing shear force determined with both load determination methods were compared to each other. Several flight maneuvers with varying loads were performed during the flight test program. This paper concentrates on the evaluation of dynamic flight maneuvers including Stalls and Pull-Up Push-Over maneuvers. The effects of changes in the aerodynamic flow characteristics during the maneuver could be detected directly with the pressure sensors based on MEMS. Time histories of the measured pressure distributions and the wing shear forces are presented and discussed.

LES analysis on the effects of baroclinic generation of vorticity on fire-wind enhancement

Substantial influence of fire flame on wind flow aerodynamic characteristics lead to enhancement of wind velocity that may cause considerable damages to buildings in bushfire-prone areas. Fire is associated with rotational vortical structures ranging from the small scales, sourced by baroclinic generation of vorticity (ωBGV), to large scale vortices arising from amalgamation mechanisms that can significantly affect wind flow characteristics during fire-wind interaction. This study aims to understand the extent to which baroclinic generation of vorticity affects wind enhanced by fire. Large eddy simulations (LES) of fire-wind interaction are conducted using fireFOAM solver of OpenFOAM platform for two different types of fuels with the aim to produce two different scenarios with similar heat release rate, but different flame temperatures. This will guarantee the production of different vortex structures in the two cases while flow expansion rate, which is proportional to the fire heat release rate, remains constant. FireFOAM solver was modified to extract fire-induced acceleration and vorticity components. The LES results show that under similar fire intensity and heat release rate conditions, wind enhancement is higher in the scenario with higher flame temperature along the centreline as well as the cross-sectional locations which are corresponding to the locations of counter-rotating vortices where the maximum wind enhancement appears. It was shown that in the case with higher flame temperature, baroclinic generation of vorticity is stronger, which causes stronger longitudinal fire-induced pressure gradient and consequently results in a higher wind enhancement in these cross-sectional locations. The distribution of maximum cross-sectional baroclinic generation of vorticity along longitudinal location are presented, confirming in both cases, baroclinic generation of vorticity reduces with an increase of distance from the fire source. However, in almost all distances, the scenario with a higher flame temperature generates stronger baroclinic generation of vorticity, so does the fire-induced pressure gradient and flow enhancement.

Aerodynamic Characteristics of Flow over Two Unsymmetrical Tandemly Arranged Airfoils – Numerical Simulation

There have been many insects having a tandem wing configuration that gives them a major advantage for maneuvering with various desirable speed, such as dragonflies and butterflies, but subsequently have been used for a wider range of applications. So, it is well known that the tandem airfoil arrangement will have better aerodynamic characteristics than those of the single airfoil arrangement. The present work aims at numerically predicting the aerodynamic characteristics of the single airfoil and tandem airfoil arrangements of the Wortmann FX 63-137 airfoil profile at a Reynolds number of 0.5 x 106. The numerical simulations are performed using commercial CFD software, ANSYS-Fluent. Turbulent flows are modeled using the k-ω RANS model with a second-order upwind scheme. The pressure-velocity coupling is done through the SIMPLE algorithm. In the tandem arrangement, airfoils are positively staggered in the flow direction with variable gaps ranging from 0.1m to 0.7m with an increment of 0.2m and the perpendicular distance between the leading edges of two airfoils is fixed at 0.3 m and simulations are performed for a various angle of attacks with a range of 0 to ± 14°. The aerodynamic characteristics of the single and tandem arrangements of the same airfoil are compared and the effect of wake from the primary airfoil on a secondary airfoil at different angles of attack is also studied for the same conditions.

Experimental investigation on compressible flow over a circular cylinder at Reynolds number of between 1000 and 5000

In the present study, a compressible low-Reynolds-number flow over a circular cylinder was investigated using a low-density wind tunnel with time-resolved schlieren visualizations and pressure and force measurements. The Reynolds number ( ) based on freestream quantities and the diameter of a circular cylinder was set to be between 1000 and 5000, and the freestream Mach number ( ) between 0.1 and 0.5. As a result, we have clarified the effect of on the aerodynamic characteristics of flow over a circular cylinder at . The results of the schlieren visualization showed that the trend of effect on the flow field, that are the release location of the Karman vortices, the Strouhal number of vortex shedding and the maximum width of the recirculation, is changed at approximately . In addition, the spanwise phase difference of the surface pressure fluctuation was captured by the measurement using pressure-sensitive paint at approximately of higher- cases. The observed spanwise phase difference is considered to relate to the spanwise phase difference of the vortex shedding due to the oblique instability wave on the separated shear layer caused by the compressibility effects. The Strouhal number of the vortex shedding is influenced by and , and those effects are nonlinear. However, the effects of and can approximately be characterized by the maximum width of the recirculation. In addition, the effect on the drag coefficient can be characterized by the maximum width of the recirculation region and the Prandtl–Glauert transformation.

Prediction of wake structure and aerodynamic characteristics of flow around square cylinders at different arrangements

Two-dimensional incompressible fluid flows around square cylinders at different arrangements have been numerically analyzed in the present work. The calculations are carried out for several values of Reynolds number (Re) ranging from 20 to 180. The results are presented in the form of vorticity contours and temporal histories of drag and lift coefficients. Besides, the physical parameters, namely, the average drag and lift coefficients and Strouhal number, are evaluated as a function of Re. Two different states of flow are predicted in the current investigation by systematically varying Re for steady and unsteady regimes. Vortex shedding is studied at different arrangements of the square cylinders allowing the investigation of three possible configurations. Special attention is paid to compute the drag and lift forces acting on the different obstacles, which allowed determining the optimal configuration in terms of both drags and lifts. The unsteady periodic wake is characterized by the Strouhal number, which varies with the Reynolds number and the obstacle geometry. The values of vortex shedding frequencies are consequently calculated in this study.

Aerodynamic Flow Characteristics of Utilizing Delta Wing Configurations in Supersonic and Subsonic Flight Regimes

Computational fluid dynamic tests are performed on delta wing models at different heights and speeds in order to achieve lift and drag coefficient values. Primarily, testing was done at supersonic speeds to reveal the advantages of these wing configurations at supersonic flight regimes at a cruise speed and altitude. The low speed characteristics are also examined, important for take-off and landing regimes where the distinctive vortices become prominent. Throughout the two flight conditions tested, a simple delta wing model (with a straight swept wing) is compared to a delta wing model that exhibited a ‘LERX’ (leading edge root extension). Provided literature describes how the performance of delta wings can be improved through this inclusion. Results obtained from the tests show that the model with the LERX has a small, but significant, performance improvement over the simple delta model, in respect to the maximum achievable lift coefficient and maximum stall angle. Lift to drag ratio is not improved however, due to the large vortices creating pressure drag. Generally, the delta wing models produce relatively small amounts of drag, and slightly less lower lift, when at low angles of attack. This is primarily due to the geometry of the models that have thin leading edges and also low thickness to chord ratios.

Design and analysis of annular combustion chamber of a low bypass turbofan engine in a jet trainer aircraft

The design of an annular combustion chamber in a gas turbine engine is the backbone of this paper. It is specifically designed for a low bypass turbofan engine in a jet trainer aircraft. The combustion chamber is positioned in between the compressor and turbine. It has to be designed based on the constant pressure, enthalpy addition process. The present methodology deals with the computation of the initial design parameters from benchmarking of real-time industry standards and arriving at optimized values. It is then studied for feasibility and finalized. Then the various dimensions of the combustor are calculated based on different empirical formulas. The air mass flow is then distributed across the zones of the combustor. The cooling requirement is met using the cooling holes. Finally the variations of parameters at different points are calculated. The whole combustion chamber is modeled using Siemens NX 8.0, a modeling software and presented. The model is then analyzed using various parameters at various stages and levels to determine the optimized design. The aerodynamic flow characteristics is simulated numerically by means of ANSYS 14.5 software suite. The air-fuel mixture, combustion-turbulence, thermal and cooling analysis is carried out. The analysis is performed at various scenarios and compared. The results are then presented in image outputs and graphs.

ХАРАКТЕРИСТИКИ ПОВІТРЯНОГО ПОТОКУ В МІКРОКАНАЛЬНОМУ КОНДЕНСАТОРІ

Heat transfer and air flow aerodynamic characteristics in the microchannel condenser are examined in the paper. These characteristics were calculated in a wide range of air velocities for a particular model of heat exchanger.

Thermal and Structural Analysis of Disc Brake for Different Cut Patterns

The thermal performance & heat dissipation of brake disc is based on aerodynamic characteristics of flow though brake disc holes. In this project, the cooling performance of two wheeler brake disc is analyzed by using two different disc designs. To analyze the effect of design on the cooling performance CFD software package, Fluent is used for simulation of air flow rate, velocity distributions, temperature contours. For these two designs, structural analysis is done in ‘Ansys workbenchstatic structural analysis’. Modeling of discs was carried out in PRO-E. KeywordsVon-Mises stress, Strain energy, Circular cut pattern, Elliptical cut pattern.

A numerical investigation on aerodynamic characteristics of an air-cushion vehicle

This paper describes a numerical study of incompressible, steady, three-dimensional turbulent air flow inside and around a simplified air-cushion vehicle (ACV) model. Two distinct cases have been studied separately regarding type of motion of the ACV; the first case is sole hovering with no forward motion where only flow through the ACV was considered, the second case is both hovering and translational motions for which the external flow around the vehicle body becomes of interest. It is assumed that both motions take place on land (above a solid plane). A hybrid mesh was generated and solutions were obtained for various lift fan pressures and air-clearance heights. Computations have been carried out by means of the computational fluid dynamics (CFD) software ANSYS FLUENT. Mean flow aerodynamic characteristics of the ACV are presented and discussed in terms of lift and drag forces, factors contributing to the drag, flow separations and singular points in the streamline patterns. The Q-criterion is employed to identify vortical structures. Differences in the aerodynamic characteristics of an ACV and a road vehicle are also discussed.

Aerodynamic Characteristics of Flow over Circular Cylinders with Patterned Surface

Aerodynamic Characteristics of Flow over Circular Cylinders with Patterned Surface

10802 三次元流れにおける溝付き正方形角柱周りの空力特性 : 高さと溝の影響(GS-03【流体(1)】)

Recently, many studies have discussed the characteristics of flow around a square cylinder, especially on the shape modification and drag coefficient. However, buildings usually have different heights and there are only a few researches on the effect of height aspect ratio to the flow characteristic. Therefore in this paper, we investigate the three-dimensional aerodynamic flow characteristics around square cylinder with grooves in different heights. We carried out wind tunnel tests to measure the drag coefficient of square cylinder with grooves. We also carried out flow visualization by a circulating water tunnel. As a result, we determined the effect of groove and aspect ratio on characteristics, under many conditions. We found that the drag coefficient of a square cylinder with larger aspect ratio has a higher drag coefficient Moreover, by applying grooves to the square cylinder, the separation flow area becomes smaller.

Hybrid Control of a Turret Wake

Effects of hybrid flow control and its active and passive components on the aerodynamic characteristics of flow over a 0.254-m-diam conformal optical aperture embedded in the hemispherical cap of a cylinder turret model (D = 0.61 m) are investigated at M = 0.3-0.5 and Re D = 4.4-7.4 x 10 6 . Resulting mean flows are characterized by surface static pressure distributions and oil-flow visualizations, while the separated-flow dynamics are assessed by hot-film measurements. Active flow control is effected by arrays of piezoelectrically driven synthetic jet modules distributed in multiple arrays upstream from the aperture. Active flow control is further assisted by global flow alterations induced by a passive forward partition plate, and, when combined, constitute hybrid flow control. It is shown that the hybrid flow control combines the positive effects of its component control elements to yield superior results in any cumulative aerodynamic aspect of the separated flow. This cumulative effect of the actuation is manifested by concomitant delay of flow separation and active, dissipative suppression of turbulent motions downstream of separation. It is also demonstrated by means of direct two-dimensional wave-front measurements that the overall aerodynamic improvements correlate with substantial suppression of optical aberrations through the separated flow. Furthermore, estimated Strehl ratios for the laser beam indicate that nearly invariant Strehl ratio is established within the range of tested aperture elevation angles, yielding improvement of about 50 % for the highest elevation angle.

Efficiency of an auto-propelled flapping airfoil

The present study deals with an investigation of the flow aerodynamic characteristics and the propulsive velocity of a system equipped with a nature inspired propulsion system. In particular, the study is aimed at studying the effect of the flapping frequency on the flow behavior. We consider a NACA0014 airfoil undergoing a vertical sinusoidal flapping motion. In contrast to nearly all previous studies in the literature, the present work does not impose any velocity on the inlet flow. During each iteration the outer flow velocity is computed after having determined the forces exerted on the airfoil. Forward motion may only be produced by flapping motion of the airfoil. This is more consistent with the physical phenomenon. The non-stationary viscous flow around the flapping airfoil is simulated using Ansys-Fluent 12.0.7. The airfoil movement is achieved using the deformable mesh technique and an in-house developed User Define Function (UDF). Our results show the influence of flapping frequency and amplitude on both the airfoil velocity and the propulsive efficiency. The resulting motion is contrasts to the applied forces. In the present study, the frequency ranges from 0.1 to 20 Hz while the airfoil amplitude values considered are: 10%, 17.5%, 25% and 40%.

CFD Analysis and Reduced Order Modeling of Uncontrolled and Controlled Laminar Flow Over a Circular Cylinder

:The main idea of flow control is the improvement of aerodynamic characteristics of flow. This study analyzes the laminar flow over a two-dimensional (2D) circular cylinder and its control by air blowing from several slots located on the cylinder surface, computationally. The Computational Fluid Dynamics (CFD) results are validated using the experimental results available in the literature for Strouhal number, time-averaged drag coefficient and pressure coefficient distribution around the cylinder. Air blowing from four slots on the cylinder with a velocity of 50% of the free-stream velocity yields a reduction of the drag coefficient by 9%. Flow structures are separated according to their frequency content by Proper Orthogonal Decomposition (POD) method. It is seen from POD results that 99% of the total energy content can be modeled by considering only four most energetic POD modes of the flow. POD analysis of the controlled cases also show that the flow structure around the cylinder changes with the help of air blowing. For real-time flow control applications, it is important to predict the flow based on surface sensors, placed at a few discrete points. In this study, optimum sensor locations on the cylinder surface are also obtained by utilization of a one-dimensional POD analysis based on surface pressure data obtained from CFD results.

Validation of computational fluid dynamics methodology used for human upper airway flow simulations

An anatomically accurate human upper airway model was constructed from multiple magnetic resonance imaging axial scans. This model was used to conduct detailed Computational Fluid Dynamics (CFD) simulations during expiration, to investigate the fluid flow in the airway regions where obstruction could occur. An identical physical model of the same airway was built using stereo lithography. Pressure and velocity measurements were conducted in the physical model. Both simulations and experiments were performed at a peak expiratory flow rate of 200L/min. Several different numerical approaches within the FLUENT commercial software framework were used in the simulations; unsteady Large Eddy Simulation (LES), steady Reynolds-Averaged Navier-Stokes (RANS) with two-equation turbulence models (i.e. k−ε, standard k−ω, and k−ω Shear Stress Transport (SST)) and with one-equation Spalart–Allmaras model. The CFD predictions of the average wall static pressures at different locations along the airway wall were favorably compared with the experimental data. Among all the approaches, standard k−ω turbulence model resulted in the best agreement with the static pressure measurements, with an average error of ∼20% over all ports. The highest positive pressures were observed in the retroglossal regions below the epiglottis, while the lowest negative pressures were recorded in the retropalatal region. The latter is a result of the airflow acceleration in the narrow retropalatal region. The largest pressure drop was observed at the tip of the soft palate. This location has the smallest cross section of the airway. The good agreement between the computations and the experimental results suggest that CFD simulations can be used to accurately compute aerodynamic flow characteristics of the upper airway.