Improvement Of Aerodynamic Performance Research Articles

Aerodynamic performance improvement of Savonius wind turbine through a passive flow control method using grooved surfaces on a deflector

A Savonius rotor is a Vertical-Axis Wind Turbine (VAWT) that converts wind force into torque on a rotating shaft. The poor efficiency of this rotor is caused by the unfavorable negative torques generated as the returning blade rotates against the incoming flow. The current study aims to improve the aerodynamic performance of a Savonius wind rotor by installing a cylinder deflector with different grooved surfaces as a unique deflector system to offset the negative impact at the wake zone downstream of the deflector. The grooved surface is essentially one way to alter the surface roughness of a cylinder, which has shown to be quite successful to control vortex shedding and wake formation behind the cylinder. In contrast to previous research, a grooved surface of a cylinder deflector was used instead of traditional deflectors to increase the aerodynamic performance by disrupting the wake zone downstream of the deflector. With this motivation, a systematic parametric study via Computational Fluid Dynamics (CFD) method was implemented for different combinations of the flow and geometric characteristics including Tip Speed Ratio (TSR) value, groove shapes (rectangular, U, and V), groove number, and size. Besides, the flow over a smooth cylinder was analyzed and compared with that of grooved cases to determine the ideal groove configurations for enhancing the total output power. The results demonstrated that the optimal deflector with the U-grooved surface augmented the aerodynamic performance the most for all TSRs. The optimal deflector has 12 U-grooved surfaces with a diameter size of 0.025 of rotor diameter. The average power coefficient enhanced dramatically up to 24.2% and 15.8% through the deflector with a U-grooved surface at TSR = 0.9 in comparison to without deflector case and smooth cylinder deflector case, respectively.

Optimization and numerical investigation of combined design of blade and endwall on rotor 67

Abstract In this work, a combined design of blade and endwall using the Extended Free Form Deformation technique is proposed and implemented on a transonic compressor rotor (the NASA Rotor 67). The best combined design is explored by numerical investigations and optimization via Kriging surrogate model method. As a result, by only modifying the hub and blade under 15 % span, the peak adiabatic efficiency is increased by 0.4 % and the overall aerodynamic performance for all operating conditions is also improved. An analysis shows that the enlarged dihedral angle between the hub and blade restrains boundary layer intersection and development. Meanwhile, the optimized hub changes the pressure distribution and prevents migration of cross-flow. As a result, the low-energy flow in the corner is accelerated downstream and the separation is limited, leading to an effective improvement in throughflow capability and aerodynamic performance in the corner region.

Aerodynamic performance improvements for a Savonius turbine above a forward-facing step via inclined solar panel: A computational study

The transformation of urban energy structure is an urgent problem to be solved in sustainable construction. To fully exploit and utilise renewable energy, this study proposes a novel wind–solar energy hybrid harvesting system that combines an inclined solar panel and a Savonius wind turbine installed on a building roof. The effects of the tilt angle of the solar panels and tip speed ratios (TSRs) on the aerodynamic performance of the turbine were investigated using high-fidelity large-eddy simulations (LES) at a Reynolds number of Re = 4.45 × 105. Five tilt angles in the range of 30°–60° were tested, and the range of TSR was 0.2–1.6. For comparison, two other installation cases were also studied, including the case of a Savonius turbine alone and the case of a single Savonius turbine placed at a fixed height position on a forward-facing step. The results showed that the power coefficient of the Savonius turbine increased and then decreased with tilt angle or TSR. When TSR = 1, the power coefficient in the system reached a maximum value of Cpmax = 0.638 at a tilt angle of 45°, 254.4% and 11.7% higher than those of the other two installation cases, respectively. The flow-field comparison results reveal why the proposed system can improve the energy harvesting efficiency. The presence of a solar panel with a suitable tilt angle increases the velocity and volume of the airflow hitting the advancing blade, creating a greater pressure difference around the blades that is caused mainly by the decrease in the low pressure on the concave surface of the advancing blade. Thus, the net torque applied to the turbine blades increases, which is conducive to driving turbine rotation. The proposed system is beneficial for improving the aerodynamic performance of Savonius turbines and the utilisation of renewable energy in urban areas.

Blade Twist Effects on Aerodynamic Performance and Noise Reduction in a Multirotor Propeller

This paper presents a novel integrated study of the aerodynamic performance and acoustic signature of multirotor propellers with a specific focus on the blade twist angle effect. Experimental measurements and computational fluid dynamic (CFD) simulations were utilized to examine and compare the aerodynamic performance and noise reduction between twisted and untwisted blades. A 2D phase-locked particle image velocimetry (PIV) was employed to visualize flow structures at specific blade locations in terms of tip vortices and trailing edge vortices. Good consistency between the simulations and measurements was observed in aerodynamic and acoustic performance. It is verified that the propellers with twisted blades enable a maximum increase of 9.3% in the figure of merit compared to untwisted blades while achieving the same thrust production and are further capable to reduce overall sound pressure level by a maximum of 4.3 dB. CFD results reveal that the twisted propeller remarkedly reduces far-field loading noise by suppressing trailing-edge vortices, hence mitigating kinetic energy fluctuation at the blade tip, while having minimal impact on thickness noise. This study points to the crucial role of blade twists in altering the aeroacoustic characteristics, indicating that optimal designs could lead to significant improvements in both aerodynamic and acoustic performance.

Aerodynamic performance improvement of a blended wing-body re-entry vehicle using ANSYS CFX

The main objective of this paper is to evaluate the aerodynamic performance of a modified blended wing-bodied re-entry vehicle by computational fluid dynamics. This analysis examines the airflow properties like pressure, density, and temperature under hypersonic flow. The study of a blended wing model at different Mach speeds and angles of attack is also included in the research paper. All the simulations in this paper are performed using the computational fluid dynamics tool of ANSYS CFX. Shear stress transport (SST) turbulence computational fluid dynamics model has been used for numerical analysis. Various inlet conditions are applied to get the aerodynamic parameters. The results revealed that the best Re-entry condition is from 10 to 20 degrees angle of attack at Mach 22, and the vehicle is very stable at a high angle of attack and Mach number. The obtained results have been validated with the public domain literature. The blended wing body has been thoroughly examined in various important locations, particularly the spacecraft nose and flap sections.

Endwall-pulsed blowing of different excitation models to control flow separation on a highly-loaded compressor cascade

Abstract Endwall-pulsed blowing (EPB) is studied for three different excitation waveforms to improve the aerodynamic performance of highly loaded compressors. Some important excitation parameters include the excitation frequency and momentum coefficient, which were analyzed in detail. The results of the EPB are compared with the endwall steady blowing (ESB) case. For EPBs with the three excitation waveforms (Waveforms sine, triangle and trapezoid), excitation frequencies that are equal to an integral multiple of the natural frequency of the vortex shedding are optimal and provide better performances than the ESB with the same time-mean momentum coefficient. Moreover, the EPBs of the three excitation waveforms have significant differences in their aerodynamic performance improvements. The optimal case is achieved by the EPB with Waveform triangle and provides a total pressure loss coefficient with a reduction of 25.64%.

Flow control with synthetic jets on two tandem airfoils using machine learning

Active flow control was applied to a tandem configuration of two SD7003 airfoils. The tandem configuration consisted of an upstream airfoil (forefoil) with a pitching motion at a fixed frequency and a downstream airfoil (hindfoil) that was not moving. Synthetic jet actuators (SJAs) were applied on both airfoils to control the flow fields at the low Reynolds number of 30 000. The flow physics inherently involved three different frequencies: frequency of the pitching forefoil and two actuation frequencies of the two of SJAs. In this study, we kept all three frequencies fixed at 5 Hz. However, we allowed for phase differences between them. An optimization study was conducted in order to improve total aerodynamic performance defined as the combined total time-averaged value of lift-to-drag ratio of both airfoils (L/D)tot. Injection angle of the two SJAs, phase differences between each SJA frequency, and frequency of the pitching motion in addition to vertical spacing between the airfoils were considered as design variables of the optimization study. Optimization algorithm was coupled with a machine learning method to reduce computational cost. We found that lift coefficients were enhanced, and drag coefficients were reduced for the optimum controlled case in comparison with the uncontrolled case, which led to an aerodynamic performance improvement of 304%. However, drag force was the dominant parameter in determining final performance value. For all design variables, drag force determined the final optimum values.

Aerodynamic Performance Improvement on NACA 4415 Airfoil by Using Cavity

This study uses a numerical method to analyze the cavity's use on the airfoil's trailing edge and the aerodynamic effects it generates. The type of airfoil used is NACA 4415. The variations in the Reynolds number examined in this study are 2×105 and 3×105. The governing equation is the Reynolds Averaged Navier-Stokes paired with the k-ε turbulence model. This study concludes that the cavity can increase Cl in the airfoil but cannot delay the stall. The increase in Cd is also a negative effect of using a cavity in the airfoil. The cavity can increase Cl by increasing the pressure on the lower side near the trailing edge. Meanwhile, the cavity increases Cd because it creates a separation of the fluid flow, forming a vortex when viewed in a streamlined form of fluid flow.

Experimental and Numerical Studies on Improvement of Aerodynamic Performance of a Semi-trailer Truck Model Using the Cabin Spoiler

Experimental and Numerical Studies on Improvement of Aerodynamic Performance of a Semi-trailer Truck Model Using the Cabin Spoiler

Aerodynamic Shape Optimization of a Symmetric Airfoil from Subsonic to Hypersonic Flight Regimes

Hypersonic flight has been the subject of numerous research studies during the last eight decades. This work aims to optimize the aerodynamic performance of a two-dimensional baseline airfoil (NACA0012) at distinct flight regimes from subsonic to hypersonic speeds. A mission profile has been defined, where four points representing the subsonic, transonic, supersonic, and hypersonic flow conditions have been selected. A framework has been implemented based on high-fidelity RANS computational fluid dynamics simulations. Gradient-based optimizations have been conducted with the objective of minimizing the drag. The optimization results show an overall improvement in aerodynamic performance, including a decrease in the drag coefficient of up to 79.2% when compared to the baseline airfoil. In the end, a morphing strategy has been laid out based on the optimal shapes produced by the optimization.

Influence of Tip Speed Ratio on the efficiency of Savonius wind turbine with deformable blades

Improving machines efficiency and searching for their new applications are the main topics in the development of the renewable energy industry. In the case of Savonius type wind turbines, the works aim at the improvement of aerodynamic performance. The CFD simulations of a turbine equipped with deformable blades showed a significant positive impact of this enhancement on the machine aerodynamic efficiency. Previously, the investigation was carried out for a TSR (Tip Speed Ratio) equal to 0.8, typically recognized as the point of maximal efficiency for conventional Savonius wind turbines with rigid blades. However, the continuously altering shape of blades during their rotation can influence the optimal TSR. Therefore, the efficiency of the deformable blade turbine was investigated in a wide range of TSR. In this paper, the previously developed quasi-2D model with a two-way Fluid-Structure Interaction method was employed to obtain turbine efficiency characteristics as a function of TSR. The maximum power coefficient Cp was achieved at TSR = 0.9. Obtained characteristic was compared with data for a conventional rigid blades turbine, gathered with a comparable sliding mesh model.

Aerodynamic performance improvement and noise control for the multi-blade centrifugal fan by using bio-inspired blades

Inspired by the swimming characteristics of carps in the C-shaped starting posture, the bionic design of the blade is developed to improve the aerodynamic performance, reduce noise and conserve energy of multi-blade centrifugal fans. By adopting the reverse engineering method, the bionic equal-thickness blades (BETBs) inspired by the C-shaped starting mid-arc of carp are designed and optimized. Based on the comparison between numerical and experimental results of the aerodynamic performance of fan, the optimal bionic equal-thickness blade (O-BETB) is obtained. When the O-BETEs are applied to the original fan, the flow rate is increased by 6.8% and the noise is reduced by 0.5 dB(A). Further, the reconstructed geometric profile of fish body is coupled into the O-BETB to improve the aerodynamic performance of the fan. The results show that the flow rate with the coupled bionic blades (CBB) is increased by 8.3%, while the noise is reduced by 1.1 dB(A), and the power and efficiency are also optimized. The internal flow field, sound field and acoustic characteristics are analyzed to reveal the generation mechanism of aerodynamic noise. The aerodynamic noise of the fan is mainly concentrated in the low and middle frequency range, and its propagation process has obvious dipole characteristics. Meanwhile, because the profile of CBB is more in line with the flow characteristics in the fan, the separation vortex and secondary-flow vortex in the impeller channel and the unsteady interaction between the blade wake-flow and the volute are significantly suppressed, which is also the main reason for the CBB to reduce the noise.

Numerical study on flow characteristics of airfoil with bionic micro-grooves

Three airfoil models with bionic micro-grooves were developed to investigate the effect of the bionic micro-grooves on the airfoil flow field and aerodynamic performance. Large eddy simulation (LES) was used to predict the flow field around the airfoil. The Re were 1.6 × 105 and 2 × 105, and the angle of attack was 6°. The results show that all three airfoils reduce the velocity gradient at the airfoil suction surface near the wall and the energy loss in the boundary layer. The area of the recirculation zone of the H1 and H2 airfoils is significantly reduced. However, when the Re is 1.6 × 105, the area of the recirculation zone of the H3 airfoil increases. The aerodynamic performance of all three airfoils was improved. When the Re is 1.6 × 105, the aerodynamic performance of the H1 airfoil is improved most significantly, and the drag reduction rate reaches 16.41%. When the Re is 2 × 105, the aerodynamic performance improvement of H2 is the most obvious, and the drag reduction rate reaches 17.45%. In order to achieve the best drag reduction effect, the position of the bionic micro-grooves should gradually approach the wing's tail with the increase of Re.

Current state and future trends in boundary layer control on lifting surfaces

Successful flow control may bring numerous benefits, such as flow stabilization, flow reattachment, separation delay, drag reduction, lift increase, aerodynamic performance improvement, energy efficiency increase, shock delay or weakening, noise reduction, etc. For these purposes, many different flow control devices, which can be classified as passive, semi-active and active, have been designed and tested. This review paper aims to highlight the most promising and commonly employed boundary layer control methods as well as outline their potential in specific applications in aerospace and energy engineering. Referenced studies, performed on various geometries (flat plates, channels, airfoils, wings, blades, cylinders), are primarily numerical or experimental. Although enhanced aerodynamic performance is achieved in many cases, further research is required to draw general conclusions. This paper aims to demonstrate that, in the future, we may expect further developments of flow control actuators, as well as their increased application.

Combining Sobolev smoothing with parameterized shape optimization

On the one hand, Sobolev gradient smoothing can considerably improve the performance of aerodynamic shape optimization and prevent issues with regularity. On the other hand, Sobolev smoothing can also be interpreted as an approximation for the shape Hessian. This paper demonstrates, how Sobolev smoothing, interpreted as a shape Hessian approximation, offers considerable benefits, although the parameterization is smooth in itself already. Such an approach is especially beneficial in the context of simultaneous analysis and design, where we deal with inexact flow and adjoint solutions, also called One Shot optimization. Furthermore, the incorporation of the parameterization allows for direct application to engineering test cases, where shapes are always described by a CAD model. The new methodology presented in this paper is used for reference test cases from aerodynamic shape optimization and performance improvements in comparison to a classical Quasi-Newton scheme are shown.

Aerodynamic performance characteristics of EYO-Series low Reynolds number airfoils for small wind turbine applications

In this study, the aerodynamic performance characteristics of three new EYO-Series low Reynolds number (Re) airfoils were tested at Re = 100,000 to 500,000, which are typical range of Re numbers encountered by airfoils of small wind turbine blades. The results generally demonstrated aerodynamic performance improvements of all three airfoils with increase in Re. EYO7-8 recorded the highest lift-to-drag ratio of 170 at Re = 500,000. EYO9-8 had the highest stall angle of 15° at all tested Re except at Re = 200,000. EYO9-8 again had gradual stall performances at all Re. All three airfoils also had good drag bucket performances where initial increases in lift were accompanied by either constant or reducing drag. The findings from this study showed that there are no significant variations in the lift performance for Re ≥ 300,000. The low variation in lift performance for the EYO-Series airfoils is desirable for the design of small wind turbine blades for low Re applications.

Active Flow Control of Helicopter Rotor Based on Coflow Jet

When a helicopter rotor undergoes flow separation, the drag of the rotor increases substantially, as does the power demand, which seriously affects the aerodynamic performance and flight safety of the helicopter. Therefore, it is crucial to research how to suppress the flow separation of rotor blades. An active control technique based on a coflow jet (CFJ) at the rotor blade tip was employed in this study to suppress the flow separation over the rotor. The mechanisms and behavior were investigated. The rotor flow field was numerically simulated by solving the Reynolds-averaged Navier–Stokes equations with the finite volume method. The turbulence model was k − ω SST, and the rotor motion was simulated using the overset mesh technique. After applying CFJ control, the airflow from the injection slot at the leading edge of the rotor increased the energy of the mainstream in the near-wall area, which enhanced its ability to resist the adverse pressure gradient. A flow separation was effectively suppressed, both on the advancing and retreating sides, which improved the aerodynamic performance of the rotor. During the whole rotation period, the thrust coefficient of the rotor increased by up to 5.6%, the moment coefficient decreased by as much as 26.8%, and the equivalent lift-to-drag ratio increased by up to 44.0%. Moreover, the effects of the CFJ parameters on the flow separation suppression of the rotor are researched. These results may provide a foundation for the development of aerodynamic performance improvement for helicopter rotor based on a CFJ.

Combined application of passive and active boundary layer aspiration in a transonic compressor rotor for shock wave/boundary layer interaction control

Shock wave/boundary layer interaction (SWBLI) is one of the key factors that limits the improvement of aerodynamic performance and stability for supersonic/transonic compressors. In this research, a combined flow control device (CFCD) was designed for controlling SWBLI in the NASA transonic compressor Rotor 35. The original flow fields for Rotor 35 were numerically analyzed first. The results show that the SWBLI is severe, resulting in much flow loss and partly leading to the compressor instability. Based on this phenomenon, the CFCD was designed with a novel three-dimensional passive self-recirculation flow channel and an active suction slot. The flow channel is mounted on the rotor blade suction surface to connect the low- and high-pressure regions ahead of and behind the shock, respectively. The effect of the CFCD on the rotor performance and corresponding working mechanism are then researched as well. With the help of CFCD, the rotor-achieved total pressure ratio (TPR) is maximally increased by 3.0%, and the stall margin (SM) is improved by 4.1% as well. But the rotor isentropic efficiency (IE) considering additional energy expenditure caused by active suction flow has the maximum increment at choke point of 0.27% and highest reduction at near-stall point of 0.54%. The working mechanisms of CFCD include two aspects: one is forming a stable and low-entropy generated lambda shock wave and the other one is reducing the magnitude of flow separation. The dominant mechanism varies with the rotor working condition and depends on whether the leading-edge shock moves upstream of the passive bleed slot.

Effects of bionic blades inspired by the butterfly wing on the aerodynamic performance and noise of the axial flow fan used in air conditioner

The axial flow fan, as a key part of the outdoor unit of air conditioner, has an important impact on the performance of air conditioner. In order to reduce the power consumption and aerodynamic noise of the outdoor unit, the outer edge profile with a depression structure, inspired by the effective control of butterfly wings for airflow, is reconstructed and adopted in the design of bionic blades. The effects of bionic blades with four different depression depths on the aerodynamic performance of the outdoor unit are investigated numerically. It is found that when the depression depth is 1.9 mm, the aerodynamic performance of the outdoor unit is the best. For the axial flow fan with the optimal design blade, the numerical simulation and experimental test on the noise of the outdoor unit are carried out. Based on the experimental results, the shaft power of the outdoor unit is reduced by 1% and the noise is reduced by 1.3 dB when the bionic blade with the depression depth of 1.9 mm is adopted. Based on the numerical results, the flow characteristics of the axial flow fan with the bionic blades is analyzed and the noise reduction mechanism of the depression structure is revealed. The studied results show that the depression structure with proper depth at the outer edge of the blades effectively changed the development and trajectory of the tip leakage vortex, which has a positive influence on the aerodynamic performance improvement and noise reduction of the axial flow fan.

Surrogate-based aerodynamic shape optimization of a morphing wing considering a wide Mach-number range

Aerodynamic shape design considering both subsonic and hypersonic performance is a challenge in the field of aerospace. Many studies have shown that morphing wing is a promising technology to address this challenge. In this article, a new morphing mechanism which changes both the plane shape (such as span and sweep angle) and the profile (such as chord length and relative thickness) of the wing is proposed and a multi-objective optimization design for this new morphing mechanism is conducted based on surrogate-based optimization (SBO) algorithm. In the optimization design, three different configurations of the morphing wing which are the 36-, 45- and 70-degree sweep angle state, respectively and four different flow conditions which are subsonic flow (0.25 Ma), transonic flow (0.85 Ma), supersonic flow (1.2 Ma) and hypersonic flow (6 Ma) are considered. 36-degree sweep angle state is used for subsonic flow, 45-degree sweep angle state is used for transonic flow and supersonic flow and 70-degree sweep angle state is used for hypersonic flow. Subsonic lift and transonic, supersonic, hypersonic lift-to-drag ratios are objectives of this optimization design which has up to 64 design variables. To reduce computational cost of high-fidelity CFD (computational fluid dynamics) simulations and find the global optimum, Kriging surrogate model combined with a parallel infill-sampling method and a multi-round strategy are employed in this study. At last, the optimized morphing wing is evaluated and compared with the baseline and a fixed wing which is a moderate sweep wing. Results show that the optimized morphing wing features a very good aerodynamic performance improvement over the flow regimes from subsonic to hypersonic flow conditions.