Optimum Profiles of Endwall Contouring for Enhanced Net Heat Flux Reduction and Aerodynamic Performance

Successfully utilized non-axisymmetric endwalls to enhance turbine efficiencies(aerodynamic and turbine inlet temperatures)by controlling the characteristics of the secondary flow in a blade passage.This is accomplished by steady-state numerical hydrodynamics and deep knowledge of the field of flow.Because of the interaction between mainstream and purge flow contributing supplementary losses in the stage,non-axisymmetric endwalls are highly susceptible to the inception of purge flow exit compared to the flat and any advantage rapidly vanishes.The conclusions reveal that the supreme endwall pattern could yield a lowering of the gross pressure loss at the design stage and is related to the size of the top-loss location being productively lowered.This has led to diminished global thermal exchange lowered in the passage of the vane alone.The reverse flow adjacent to the suction side corner of the endwall is migrated farther from the vane surface,as the deviated pressure spread on the endwall accelerates the flow and progresses the reverse flow core still downstream.The depleted association between the tornado-like vortex and the corner vortex adjacent to the suction side corner of the endwall is the dominant mechanism of control in the contoured end wall.In this publication,we show that the non-axisymmetric endwall contouring by selective numerical shape change method at most prominent locations is advantageous in lowering the thermal load in turbines to augment the net heat flux reduction as well as the aerodynamic performance using multi-objective optimization.

Study on Aerodynamic Performance of Wind Turbine Airfoil Synthesized by Mean Camber Line Superposition Thickness between Bionic and Traditional Airfoil Bionic and Traditional Airfoil

The aerodynamic performance of wind turbine needs to be improved day by day.In this paper,the bionic airfoil of wind turbine and the traditional airfoil are combined to optimize the aerodynamic performance.The new airfoil is synthesized by the method of the mean camber line superposition thickness synthesis.The flow field characteristics of 4 synthetic airfoils were calculated by using the numerical simulation of CFD commercial software Fluent,and compared with 3 original airfoils,new airfoils of different shapes were obtained,and an incomplete synthetic parameterization method for airfoils optimization was proved,which has certain engineering practical value.

Effect of landform on aerodynamic performance of high-speed trains in cutting under cross wind

The effects of the different landforms of the cutting leeward on the aerodynamic performance of high-speed trains were analyzed based on the three-dimensional, steady, and incompressible Navier-Stokes equation and k-e double-equation turbulent model. Results show that aerodynamic forces increase with the cutting leeward slope decreasing. The maximum adding value of lateral force, lift force, and overturning moment are 147%, 44.3%, and 107%, respectively, when the slope varies from 0.67 to -0.67, and the changes in the cutting leeward landform have more effects on the aerodynamic performance when the train is running in the line No. 2 than in the line No. 1. The aerodynamic forces, except the resistance force, sharply increase with the slope depth decreasing. By comparing the circumstance of the cutting depth H=-8 m with that of H=8 m, the resistance force, lateral force, lift force, and overturning moment increase by 26.0%, 251%, 67.3% and 177%, respectively. With the wind angle increasing, the resistance force is nonmonotonic, whereas other forces continuously rise. Under three special landforms, the changes in the law of aerodynamic forces with the wind angle are almost similar to one another.

Effect of Streamlined Nose Length on the Aerodynamic Performance of a 800 km/h Evacuated Tube Train

The aerodynamic resistance of a train running in the open air limits the maximum speed that can be attained by the train.For this reason,evacuated tube trains(ETT)are being considered as valid alternatives to be implemented in the future.The atmosphere in the tube,the so-called blocking ratio and the length of the streamlined nose are the key factors affecting the aerodynamic performances of these trains.In the present work,we investigate evacuated tube trains with different lengths of the streamline nose on the basis of computational fluid dynamics(CFD).The three-dimensional steady compressible Navier-Stokes equations are solved.The running speed of the ETT is 800 km/h and the blocking ratio is 0.2.Results show that with the increase of the streamlined nose length,the aerodynamic drag and lift forces of the head car decrease gradually,and the drag and lift forces of the middle car change slightly.For the tail car,the drag force decreases,whereas the absolute value of the lift force increases.At a speed of 800 km/h,a slight shock wave appears at the rear of the tail car,which affects the aerodynamic forces acting on the train.

Numerical Investigations on the Aerodynamic Performance of Wind Turbine： Downwind Versus Upwind Configuration

Although the upwind configuration is more popular in the field of wind energy, the downwind one is a promising type for the offshore wind energy due to its special advantages. Different configurations have different aerodynamic performance and it is important to predict the performance of both downwind and upwind configurations accurately for designing and developing more reliable wind turbines. In this paper, a numerical investigation on the aerodynamic performance of National Renewable Energy Laboratory （NREL） phase V1 wind turbine in downwind and upwind configurations is presented. The open source toolbox OpenFOAM coupled with arbitrary mesh interface （AMI） method is applied to tackle rotating problems of wind turbines. Two 3D numerical models of NREL phase VI wind turbine with downwind and upwind configurations under four typical working conditions of incoming wind velocities are set up for the study of different unsteady characteristics of the downwind and upwind configurations, respectively. Numerical results of wake vortex structure, time histories of thrust, pressure distribution on the blade and limiting streamlines which can be used to identify points of separation in a 3D flow are presented. It can be concluded that thrust reduction due to blade-tower interaction is small for upwind wind turbines but relatively large for downwind wind turbines and attention should be paid to the vibration at a certain frequency induced by the cyclic reduction for both configurations. The results and conclusions are helpful to analyze the different aerodynamic performance of wind turbines between downwind and upwind configurations, providing useful references for practical design of wind turbine.

Aerodynamic performance analysis of trains on slope topography under crosswinds

This work used the computational fluid dynamics method combined with full-scale train tests to analyze the train aerodynamic performance on special slope topography. Results show that with the increment in the slope gradient, the aerodynamic forces and moment increase sharply. Compared with the flat ground condition, the lateral force, lift force, and overturning moment of the train on the first line increase by 153.2%, 53.4% and 124.7%, respectively, under the slope gradient of 20°. However, with the increment of the windward side's depth, the windbreak effect is improved obviously. When the depth is equal to 10 m, compared with the 0 m, the lateral force, lift force and overturning moment of the train on the first line decrease by 70.9%, 77.0% and 70.6%,respectively. Through analyzing the influence of slope parameters on the aerodynamic performance of the train, the relationships among them are established. All these will provide a basic reference for enhancing train aerodynamic performances under different slope conditions and achieve reasonable train speeds for the operation safety in different wind environments.

Influence of ribs on train aerodynamic performances

The influence of ribs on the train aerodynamic performance was computed using detached eddy simulation(DES), and the transient iteration was solved by the dual-time step lower-upper symmetric Gauss-Seidel(LU-SGS) method. The results show that the ribs installed on the roof have a great effect on the train aerodynamic performance. Compared with trains without ribs, the lift force coefficient of the train with convex ribs changes from negative to positive, while the side force coefficient increases by 110%and 88%, respectively. Due to the combined effect of the lift force and side force, the overturning moment of the train with convex ribs and cutting ribs increases by 140% and 106%, respectively. There is larger negative pressure on the roof of the train without ribs than that with ribs. The ribs on the train would disturb the flow structure and contribute to the air separation, so the separation starts from the roof, while there is no air separation on the roof of the train without ribs. The ribs can also slow down the flow speed above the roof and make the air easily sucked back to the train surface. The vortices at the leeward side of the train without ribs are small and messy compared with those of the train with convex or cutting ribs.

Lateral aerodynamic performance and speed limits of double-deck container vehicles with different structures

Based on 3D, steady N-S equations and k-e turbulence model, Fluent was employed to do numerical simulation for lateral aerodynamic performance of 6-axis X2K double-deck container trains with two different loading forms, and speed limits of the freight trains were studied. The result indicates that under wind environment： 1） As for vehicles without and with cross-loaded structure, aero-pressure on the former is bigger, but air velocity around the latter is larger; 2） When sideslip angle θ=0°, the airflow is symmetry about train vertical axis; when θ〉0°, the airflow is detached at the top of vehicles, and the air velocity increases above the separated line but decreases below it; 3） With θ increasing, the lateral force on the mid vehicle firstly increases but decreases as θ=75°; 4） When the 6-axis X2K fiat car loads empty boxes of a 40 ft and a 48 ft at 120 km/h, the overturning wind speed is 25.19 m/s, and the train should be stopped under the 12th grade wind speed.

Effect of car-body lower-center rolling on aerodynamic performance of a high-speed train

The interaction between the car-body vibration and aerodynamic performance of the train becomes more prominent motivated by the vehicle’s light-weighting design.To address this topic,this study firstly analyzes the posture characteristics of the car-body based on the previous full-scale test results.And then the aerodynamic performance under different vibration cases(different car-body roll angles)is studied with an improved delayed detached eddy simulation(IDDES).The results revealed that car-body rolling had a significant impact on the aerodynamic behavior of bogies,which significantly increased the lateral force and yaw moment of a bogie and further may have aggravated the operational instability of the train.The unbalanced distribution of the longitudinal pressure on both sides of the bogie caused by the car-body rolling motion was the primary cause for the bogie yaw moment increase.The tail vortex of the train was also affected by the car-body rolling,resulting in vertical jitter.

PREDICTION OF THE AERODYNAMIC PERFORMANCE OF HORIZONTAL AXIS WIND TURBINES IN CONDITION OF UNIFORM WIND

The classical momentum-blade element theory is improved by using the empirical formula while part of rotor blades enters into the turbulent wake state, and the performance of a horizontal-axis wind turbine (HAWT) at all speed ratios can be predicted. By using an improved version of the so-called secant method, the convergent solutions of the system of two-dimensional equations concerning the induced velocity factors a and a' are guaranteed. Besides, a solving method of multiple solutions for a and a' is proposed and discussed. The method provided in this paper can be used for computing the aerodynamic performance of HAWTs both ofrlow solidity and of high solidity. The calculated results coincide well with the experimental data.

Corrugated surface microparticles with chitosan and levofloxacin for improved aerodynamic performance

Corrugated surface microparticles comprising levofloxacin(LEV),chitosan and organic acid were prepared using the 3-combo spray drying method.The amount and the boiling point of the organic acid affected the degree of roughness.In this study,we tried to improve the aerodynamic performance and increase aerosolization by corrugated surface microparticle for lung drug delivery efficiency as dry powder inhaler.HMP175 L20 prepared with 175 mmol propionic acid solution was corrugated more than HMF175 L20 prepared with 175 mmol formic acid solution.The ACI and PIV results showed a significant increase in aerodynamic performance of corrugated microparticles.The FPF value of HMP175 L20 was 41.3%±3.9%compared with 25.6%±7.7%of HMF175 L20.Corrugated microparticles also showed better aerosolization,decreased x-axial velocity,and variable angle.Rapid dissolution of drug formulationswas observed in vivo.Lowdoses administered to the lungs achieved higher LEV concentrations in the lung fluid than high doses administered orally.Surface modification in the polymer-based formulation was achieved by controlling the evaporation rate and improving the inhalation efficiency of DPIs.

Prediction of Wing Aerodynamic Performance in Rain Using Neural Net

A new method for prediction of wing aerodynamic performance in rain condition was presented.Three-and four-layer artificial neural networks based on improved algorithm for error Back Propagation(BP)network were respectively built.Detailed approaches to determine the optical parameters for network model were introduced and the specific steps for applying BP network model to predict wing aerodynamic performance in rain were given.On this basis,the established optimal three-and four-layer BP network model was used for this prediction.Results indicate that both of the network models are appropriate for predicting wing aerodynamic performance in rain.The sum of square error level produced by two models is less than 0.2%,and the prediction accuracy by four-layer network model is higher than that of three-layer network.

Effect of streamlined nose length on aerodynamic performance of high-speed train with a speed of 400 km/h

The streamlined nose length(SNL)plays a crucial role in determining the aerodynamic performance of high-speed trains.An appropriate SNL can not only effectively reduce the magnitude of aerodynamic drag and lift forces,but also improve the performance of the high-speed train in tunnel passing and crosswind circumstances.In this study,a numerical simulation of the aerodynamic performance of high-speed trains at a speed of 400 km/h,with varying SNLs,is conducted using the k-ωshear stress transport(SST)turbulence model.The different SNLs include 6.0,7.0,8.0,9.0,9.8,12.0,15.0,and 18.0 m.In order to validate the accuracy of the numerical simulation,its results are compared with wind tunnel test data obtained from the literature.Numerical simulation is carried out using compressible and incompressible gases to determine the effect of gas compressibility on results.The impact of SNL on the aerodynamic performance of the trains is analyzed in terms of aerodynamic forces,velocity,and pressure distributions.In comparison to the original train,the train with a 6.0 m SNL experienced a 10.8%increase in overall aerodynamic resistance.Additionally,the lift forces on the head and tail cars increased by 35.7%and 75.5%,respectively.On the other hand,the train with an 18.0 m SNL exhibited a 16.5%decrease in aerodynamic drag.Furthermore,the lift forces on the head and tail cars decreased by 21.9%and 49.7%,respectively.The aerodynamic drag force of the entire train varies linearly with the SNL,while the aerodynamic lift of the tail car follows a quadratic function in relation to the SNL.

Aerodynamic Performance of Three Flapping Wings with Unequal Spacing in Tandem Formation

To better understand the aerodynamic reasons for highly organized movements of flying organisms,the three-flapping wing system in tandem formation was studied numerically in this paper.Different from previous relevant studies on the multiple flapping wings that are equally spaced,this study emphasizes the impact of unequal spacing between individuals on the aerodynamics of each individual wing as well as the whole system.It is found that swapping the distance between the first and second wing with the distance between the second wing and the rearmost wing does not affect the overall aerodynamic performance,but significantly changes the distribution of aerodynamic benefits across each wing.During the whole flapping cycle,three effects are at play.The narrow channel effect and the downwash effect can promote and weaken the wing lift,respectively,while the wake capture effect can boost the thrust.It also shows that these effects could be manipulated by changing the spacing between adjacent wings.These findings provide a novel way for flow control in tandem formation flight and are also inspiring for designing the formation flight of bionic aircraft.

Enhancing Aerodynamic Performances of Highly Loaded Compressor Cascades via Air Injection

This article experimentally studies the effects of air injection near the blade trailing edge on flow separation and losses in a highly loaded linear compressor cascade. Aerodynamic parameters of eight cascades with different air injection slot configura- tions are measured by using a five-hole probe at the cascade outlets. Ink-trace flow visualization is performed to obtain the flow details around the air injection slots. The static pressure distribution is clarified with pressure taps on the endwalls. The...

Influence of leading edge with real manufacturing error on aerodynamic performance of high subsonic compressor cascades

To investigate the influence of real leading-edge manufacturing error on aerodynamic performance of high subsonic compressor blades,a family of leading-edge manufacturing error data were obtained from measured compressor cascades.Considering the limited samples,the leadingedge angle and leading-edge radius distribution forms were evaluated by Shapiro-Wilk test and quantile–quantile plot.Their statistical characteristics provided can be introduced to later related researches.The parameterization design method B-spline and Bezier are adopted to create geometry models with manufacturing error based on leading-edge angle and leading-edge radius.The influence of real manufacturing error is quantified and analyzed by self-developed non-intrusive polynomial chaos and Sobol’indices.The mechanism of leading-edge manufacturing error on aerodynamic performance is discussed.The results show that the total pressure loss coefficient is sensitive to the leading-edge manufacturing error compared with the static pressure ratio,especially at high incidence.Specifically,manufacturing error of the leading edge will influence the local flow acceleration and subsequently cause fluctuation of the downstream flow.The aerodynamic performance is sensitive to the manufacturing error of leading-edge radius at the design and negative incidences,while it is sensitive to the manufacturing error of leading-edge angle under the operation conditions with high incidences.

EXPERIMENTAL RESEARCH ON AERODYNAMIC PERFORMANCE AND EXIT FLOW FIELD OF LOW PRESSURE AXIAL FLOW FAN WITH CIRCUMFERENTIAL SKEWED BLADES

In this article, the low pressure axial flow fan with circumferential skewed rotor blade, including the radial blade, the forward-skewed blade and the backward-skewed blade, was studied with experimental methods. The aerodynamic performance of the rotors was measured. At the design condition at outlet of the rotors, detailed flow measurements were performed with a five-hole probe and a Hot-Wire Anemometer （HWA）. The results show that compared to the radial rotor, the forward-skewed rotor demonstrates a wider Stable Operating Range （SOR）, is able to reduce the total pressure loss in the hub region and make main loading of blade accumulating in the mid-span region. There is a wider wake in the upper mid-span region of the forward-skewed rotor. Compared to the radial rotor, in the backward-skewed rotor there is higher total pressure loss near the hub and shroud regions and lower loss in the mid-span region. In addition, the velocity deficit in the wake is lower at mid-span of the backward-skewed rotor than the forward-skewed rotor.

Aerodynamic performance enhancement forflapping airfoils by co-flow jet

Introducing active flow control into the design of flapping wing is an effective way to enhance its aerodynamic performance.In this paper,a novel active flow control technology called Co-Flow Jet(CFJ)is applied to flapping airfoils.The effect of CFJ on aerodynamic performance of flapping airfoils at low Reynolds number is numerically investigated using Unsteady Reynolds Averaged Navier-Stokes(URANS)simulation with Spalart-Allmaras(SA)turbulence model.Numerical methods are validated by a NACA6415-based CFJ airfoil case and a S809 pitching airfoil case.Then NACA6415 baseline airfoil and NACA6415-based CFJ airfoil with jet-off and jet-on are simulated in flapping motion,with Reynolds number 70,000 and reduced frequency 0.2.As a result,CFJ airfoils with jet-on generally have better lift and thrust characteristics than baseline airfoils and jet-off airfoil when Cμgreater than 0.04,which results from the CFJ effect of reducing flow separation by injecting high-energy fluid into boundary layer.Besides,typical kinematic and geometric parameters,including the reduced frequency and the positions of the suction and injection slot,are systematically studied to figure out their influence on aerodynamic performance of the CFJ airfoil.And a variable Cμjet control strategy is proposed to further improve effective propulsive efficiency.Compared with using constant Cμ,an increase of effective propulsive efficiency by22.6%has been achieved by using prescribed variable CμNACA6415-based CFJ airfoil at frequency 0.2.This study may provide some guidance to performance enhancement for Flapping wing Micro Air Vehicles(FMAV).

Aerodynamic performance of owl-like airfoil undergoing bio-inspired flapping kinematics

Natural flyers have extraordinary flight skills and their prominent aerodynamic performance has attracted a lot of attention.However,the aerodynamic mechanism of birds’flapping wing kinematics still lacks in-depth understanding.In this paper,the aerodynamic performance of owl-like airfoil undergoing bio-inspired flapping kinematics extracted from a free-flying owl wing has been numerically investigated.The overset mesh technique is used to deal with the large range movements of flapping airfoils.The bio-inspired kinematics consist of plunging and pitching movement.A pure sinusoidal motion and a defined motion composed of plunging of sinusoidal motion and pitching of the bio-inspired kinematics are selected for comparison.The other two NACA airfoils are also selected to figure out the advantages of the owl-like airfoil.It is found that the cambered owl-like airfoil can enhance lift during the downstroke.The bio-inspired kinematics have an obvious advantage in lift generation with a presence of higher peak lift and positive lift over a wider proportion of the flapping cycle.Meanwhile,the bio-inspired motion is more economical for a lower power consumption compared with the sinusoidal motion.The sinusoidal flapping motion is better for thrust generation for a higher peak thrust value in both upstroke and downstroke,while the bio-inspired kinematics mainly generate thrust during the downstroke but produce more drag during the upstroke.The defined motion has similar lift performance with the bio-inspired kinematics,while it consumes more energy and generates less thrust.The unsteady flow field around airfoils is also analyzed to explain the corresponding phenomenon.The research in this paper is helpful to understand the flight mechanism of birds and to design a micro air vehicle with higher performance.

Effect of Gurney flap on flow separation and aerodynamic performance of an airfoil under rain and icing conditions

In the present study,special attention is paid to numerically investigate the aerodynamic performance of the NACA 0012 airfoil under rain and icing conditions with the aim to better understand the severe aerodynamic performance penalties of aircraft in flight.Furthermore,in order to control the flow separation and improve the aerodynamic performance of the airfoil under critical atmospheric conditions,the Gurney flap with different heights is attached to the trailing edge of the airfoil.The simulation is done at a Reynolds number of 3.1 × 105 under different atmospheric conditions including dry,rain,icing and coupling of rain and icing conditions.A two-way momentum coupled Eulerian-Lagrangian multiphase method is used to simulate the process of water film layer formed on the airfoil surface due to rainfall.According to the results,accumulation of water due to rainfall and ice accretion on the airfoil surface inevitably provides notable negative effects on the aerodynamic performance of the airfoil.It is concluded that icing induces a higher aerodynamic degradation than rain due to very intensive ice accretion.The Gurney flap as a passive flow control method with a favorable height for each condition is very beneficial.The maximum increment of the lift-to-drag ratio is achieved by Gurney Hap with a height of 0.01 of airfoil chord length for dry and rain conditions and 0.02 of airfoil chord length for icing and coupling of rain and icing conditions,respectively.