Blade Loading Research Articles

Noise Characteristics of Automobile Cooling Fan Based on Circumferential Mode Analysis

Abstract The fan is the main component of the cooling system of an automobile engine. A typical automobile cooling fan consists of a shrouded axial fan, stator vanes, a deflector, and a cover. With recent developments in the automobile industry, the increase in the speed of rotation and blade load of cooling fans has increased the noise generated by them. To reduce it, it is important to analyze the characteristics of this noise. This paper uses an acoustic test to examine the characteristics of flow and noise of automobile cooling fans. The frequency spectrum and far-field radiation of the noise of the fan are first analyzed through far-field measurements, and the influence of the single rotor, tip clearance of the blade, and cover on fan noise is studied. The distribution of the mode spectrum and characteristics of sound propagation of discrete tonal noise are then examined using the circumferential mode test. The influence of the flow structure on fan noise is also studied. The flow characteristics and distribution of the source of noise of the automobile cooling fan are then used to analyze the influence of the structure of the fan on the noise generated by it. The results can help develop designs to reduce the noise of automobile cooling fans.

A variable twist blade for horizontal axis wind turbines: Modeling and analysis

A method for analyzing the performance of a wind turbine blade design with an adaptive variable twist is presented. The possibility of implementing morphing features is becoming increasingly possible with innovative materials and manufacturing techniques. This motivates a blade concept consisting of multiple shell sections mounted on a rigid spar and covered by non-structural skin. The design allows the blade shells to adapt the twist angle distribution (TAD). The study is conducted using data acquired from the National Renewable Energy Laboratory (NREL) 20 kW wind turbine. A design problem is formulated to find the TAD that maximizes the aerodynamic efficiency for a discrete set of points that represent the Region 2 wind speed. The TAD is found for each point using a heuristic search algorithm. This algorithm searches through performance data that is acquired using the AeroDyn open source simulation software. Results from the model are validated with computational fluid dynamics (CFD) simulations using the Reynolds-averaged Navier-Stokes equations with the k-ω shear stress transport turbulence model. Through this first part of the analysis, it becomes possible to understand the required amount of blade deformation by the TAD function. Given this understanding, a stress analysis can be performed on the blade structure. The scenario considers the combined effect of twisting with aerodynamic loading. The blade load is determined by combining CFD with finite element analysis to facilitate the one-way fluid-structural interaction. The outcome of this work demonstrates how the proposed method can be used to determine the gain in efficiency, required range of motion, and structural performance of the blade shells for a given wind turbine blade design.

A Robust Procedure to Implement Dynamic Stall Models Into Actuator Line Methods for the Simulation of Vertical-Axis Wind Turbines

Abstract The actuator line method (ALM), combining a lumped-parameter representation of the rotating blades with the computational fluid dynamics (CFD) resolution of the turbine flow field, stands out among the modern simulation methods for wind turbines as probably the most interesting compromise between accuracy and computational cost. Being however a method relying on tabulated coefficients for modeling the blade-flow interaction, the correct implementation of the submodels to account for higher-order aerodynamic effects is pivotal. Inter alia, the introduction of a dynamic stall model is extremely challenging: first, it is important to extrapolate a correct value of the angle of attack (AoA) from the solved flow field; second, the AoA history needed to calculate the rate of dynamic variation of the angle itself is characterized by a low signal-to-noise ratio, leading to severe numerical oscillations of the solution. The study introduces a robust procedure to improve the quality of the AoA signal extracted from an ALM simulation. It combines a novel method for sampling the inflow velocity from the numerical flow field with a low-pass filtering of the corresponding AoA signal based on cubic spline smoothing (CSS). Such procedure has been implemented in the actuator line module developed by the authors for the commercial ansysfluent solver. To verify the reliability of the methodology, two-dimensional (2D) unsteady Reynolds-averaged Navier–Stokes (URANS) simulations of a test two-blade Darrieus H-rotor, for which high-fidelity experimental and numerical blade loading data were available, have been performed for a selected unstable operation point.

The Effect of Windscreens and Walkways on Air-Cooled Condenser Performance and Fan Blade Dynamic Loading

Abstract This paper presents a relative comparison of the impact of cruciform screens, perimeter screens, and walkways on 3 × 6 cells forced draft air-cooled condenser's (ACC) thermal performance and dynamic fan blade loading under windy conditions. Numerical simulations were carried out for the three mitigation measures at two fan platform heights, four wind speeds, and three wind directions. The results indicate that walkways are a robust solution to ACC wind effects and offer benefits in terms of thermal performance and dynamic blade loading under all wind conditions considered. Cruciform screens offered the most effective mitigation of wind-related thermal performance deterioration under certain wind conditions, but the impact of these screens is sensitive to the wind direction. The dynamic blade loading impact of cruciform screens is variable, and these screens are not recommended for dynamic blade loading mitigation. Perimeter screens offered the most effective mitigation of dynamic blade loading and were particularly effective at high wind speeds but often exacted a penalty in terms of thermal performance at moderate to low wind speeds. The results of this study indicate that a correctly configured wind mitigation system, potentially consisting of more than one individual mechanism, could help improve thermal performance and simultaneously reduce dynamic blade loading under windy conditions resulting in a robust, wind-resistant condenser.

Some effects of non-axisymmetric tip clearance layout on axial compressor aerodynamics

A steady and unsteady numerical research is carried out to explore some effects of a specific non-axisymmetric tip clearance layout on the overall performance and stability of an axial compressor stage. For a 4-stage low-speed research compressor (LSRC) in Shanghai Jiao Tong University (SJTU), one-eighth annulus of the inlet guide vane and the first stage rotor was modeled for this study. After the validation for the uniform tip clearance case, a specific non-axisymmetric tip clearance layout is chosen from several random cases generated by the Gaussian Probabilistic Density Function method. Unsteady time-averaged results at the near stall condition show that the chosen non-axisymmetric layout can improve the isentropic efficiency by 1.3% and extend the stall margin by 4%. Detailed analyses on flow fields are carried out to interpret the performance improvement. Due to the circumferential layout of clearance sizes, the inlet mass flow and incidence are redistributed in both the radial and circumferential directions. It leads to blade loading and tip leakage flow varying with the tip clearance size. The quantification of blockage manifests that the blockage arising from the tip leakage flow is significantly alleviated in the non-axisymmetric layout, which leads to improvements in overall performance and stall margin. Transient flow fields at the rotor tip are also analyzed at the near stall condition. For the non-axisymmetric layout, low-momentum regions originating from larger clearance sizes oscillate and develop downstream in one blade passage period.

Numerical Study on Multiple-Blade-Rate Unsteady Propeller Forces for Underwater Vehicles

_ The unsteady propeller forces of an underwater vehicle were numerically simulated using computational fluid dynamics to investigate the effects of the axial location of the stern planes. A benchmark study was undertaken using a three-bladed propeller; experimental results of the nominal inflow wake profile were analyzed and the unsteady propeller forces were measured. The numerical method was applied to predict the unsteady propeller forces in the SUBOFF model’s wake by varying the axial locations of the stern planes. Several remarks were made on the primary harmonics of the hull’s wakes and blade-rate propeller forces. Introduction The hydroacoustic noise, which matches multiples of the number of propeller blades and its rotational speed, known as “blade-rate (BR) noise,” has been increasingly used to manage hydroacoustics for naval vessels. BR noise can be caused by alternating blade loads owing to fluctuations in the angle of attack of the blades because marine propellers are operated in the nonuniform wake of ships’ hulls. The unsteady blade load produces unsteady propeller forces that are transmitted via the propeller shaft and bearing, thus producing undesirable vibration and noise. Although the resultant BR noise is a common issue for marine vessels, in particular, submarines and other underwater vehicles deployed for undersea defense systems and oceanographic survey systems require strict specifications for the acoustic signature. Therefore, the unsteady propeller forces must be improved for reduced detectability, because the vehicles should be able to operate without being discovered while sonar detection technology continues to improve.

Extrapolation and inversion of near-field propeller noise measurements

This paper describes an experimental method for making high resolution measurements of the tonal noise from a UAV propeller in the acoustic near-field and then methods of using this data to predict blade loading, via inversion, and the radiated ‘steady loading’ and ‘thickness’ tones, via extrapolation. The experimental method uses a traversing probe microphone to measure the acoustic pressure along an axial line outboard of the propeller tip. The acoustic pressures were then ensemble averaged over many propeller revolutions. Because of the azimuthal periodicity of the ensemble-average pressure field produced by the propeller, the measured data was used to infer the pressure on a cylinder enclosing the propeller. These measurements are compared with a noise prediction made using data from a computational fluid dynamics simulation of the same propeller and are found to be in reasonable agreement – with differences attributed to the small differences in the predicted and actual blade loading distributions. Because of the high amplitude and evanescent nature of the near-field pressure produced by a propeller, measurements were made in a non-anechoic environment and were relatively unaffected by background noise or reverberation effects. The near-field acoustic data was used as input to an inverse problem to estimate the aerodynamic loading distribution on the propeller blades. The method was applied first to the numerical data for validation and then to the experimental data as a demonstration. The reconstructed loading distributions were then used as input to a method for calculating the radiated acoustic field and the predictions show good agreement with a direct projection using the measured near-field experimental data.

A numerical study for correlating performance versus number of blades and investigating flow characteristics and loss generation of an automotive radial flow turbine

Hybridization of engines is the future technology to overcome the increasing emissions of CO2 and pollutants from internal combustion engines. So far, the current technology, called downsizing, involves reducing engine size while maintaining continuous engine boosting with a turbocharger. It is well known that the radial turbine, an essential component of turbochargers, is a seat of various loss mechanisms such as incidence losses which significantly affect performance. As a contribution for further improving performance and reducing loss generation in radial turbines, this study investigates the effect of the blade number on performance and loss generation within a radial turbine of small scale turbocharger. To this end, six radial turbines were designed with several blade numbers ranging from three up to thirteen. The flow solution was computed by solving the Navier-Stokes equations using a CFD solver. The numerical results were validated against experiments. The results revealed that the impeller of 11 blades provides better performance than the other investigated designs. The results showed a substantial effect of the number of blades on the distribution of flow characteristics and loss generation. The efficiency, mass flow rate, output torque, blade loading, and leakage flow through the clearance gap of the turbine were correlated to the number of blades.

Aerodynamic performance of semi-submersible floating wind turbine under pitch motion

Pitch motion is a critical factor that affects the aerodynamic load of blades and the motion response of the floating platform. To study the effects of pitch motion, the NREL 5-MW is analyzed by using Computational Fluid Dynamics (CFD) method. The motion of the wind turbine and the floating platform is dealt with dynamic fluid–solid interaction technology. The mesh in the blade rotation domain and the motion domain are sliding mesh and overlapped mesh respectively. The Fluid Volume Fraction (VOF) method is utilized to generate and track the free surface of the ocean wave. By setting the frequencies and amplitudes of sinusoidal pitch motion, the distributed aerodynamic pressure coefficient of the cross-sections is studied along the blade spanwise direction, and the instantaneous thrust, the turbine power coefficient and the wake vortex structure are analyzed. For blade only cases, results show that the pressure coefficient near the leading edge of each spanwise blade section reaches a maximum at the half-cycle, and the turbine power output is in phase with the pitch motion. For fully coupled cases, both the frequency of the turbine thrust and pitch motion is determined by the incident wave but in a reversed phase.

Investigation of fundamental mechanism leading to the performance improvement of vertical axis wind turbines by deflector

Wind energy utilization in urban areas revives the interests in vertical axis wind turbine (VAWT). An upstream deflector has demonstrated to increase the overall efficiency of two closely spaced VAWTs more than 30% in previous experiment research. However, the optimal geometrical configuration and the mechanisms driving the performance improvement have not been fully investigated. In this study, a parametric investigation is conducted to obtain deeper fluid-mechanical insights into the interactions between two VAWTs and the deflector. The instantaneous blade load, averaged rotor torque coefficient, and near-field flow are obtained in different layouts to assess the wind turbine aerodynamic performance. The numerical results show that the blade experiences a larger relative velocity and favorable angle of attack under the influence of a deflector. There is an optimal configuration for the two wind turbines with a deflector, which increases the maximum torque coefficient by 23% relative to the configuration without a deflector. The use of the deflector affects the wake recovery to a location downstream in comparison with the no-deflector setup. Furthermore, the performance of the twin VAWTs is sensitive to the wind directions. In the skewed incoming flow, the twin VAWTs still have a better performance under the influence of a deflector.

Roles of recirculating bubble on the performance of centrifugal compressors

Research works over the years have identified a recirculating bubble locating at impeller shroud in centrifugal compressor operating under off-design conditions. However, its roles on compressor performance have been traditionally oversimplified. In this paper, the characteristics of the recirculating bubble and the full extent of its impact on compressor performance are analyzed through a well-validated three-dimensional numerical simulation. The simulation results show that the bubble is initiated within the impeller passage and stretches gradually in both streamwise and spanwise directions with decreasing flowrates. During this process, it continues to reshape the effective area and flow conditions at the impeller inlet through its effects of blockage, preheating, and preswirl. The evolution of the recirculating bubble can be divided into two phases depending on whether the center of the recirculating bubble passes beyond the impeller inlet. In the initial phase, the blockage rapidly increases and helps to alleviate the impeller incidence and the relevant losses of the active flow. Meanwhile, the negative effects of preheating and preswirl remain relatively low. In the secondary phase, the upstream propagation of the recirculating bubble speeds up and reinforces its negative effects of preheating and preswirl. The fact that the positive and negative effects are not synchronous implies different roles that the bubble plays in the two phases. A model is established to characterize the effects of the recirculating bubble. A combination of the model and a single-zone meanline method is then employed to quantitatively assess the roles of the recirculating bubble by comparing the compressor performance with and without the bubble. The results show that in the initial phase, the recirculating bubble acted as a positive role in suppressing the incidence loss, the tip clearance loss, and the blade loading loss, leading to higher compressor efficiency. However, in the secondary phase, the negative effects overwhelmed the positive effects, which deteriorated the efficiency. The implications of the two-phase evolution of the recirculating bubble on centrifugal compressor design and flow control are also discussed.

Benefits and Challenges of the Inside-Out Ceramic Turbine: An Experimental Assessment

Distributed aircraft propulsion has renewed the interest in power-dense, high-efficiency power packs. Ceramic turbomachinery could be a major enabler, although no successful design has been achieved in microturbine rotors. Rotor blade loading is tensile and a hurdle for successful conversion to ceramics. The inside-out ceramic turbine (ICT) rotor uses the superior compressive properties of monolithic ceramics by supporting ceramic blades against a structural composite rotating shroud. This enables low stress levels throughout the blade, increasing reliability and extending service life. An experimental demonstration of two ICT designs was conducted with 15-kW scale prototypes to identify critical issues: design A, a flexible hub that clamps blades against the structural shroud and design B, a sliding-blade configuration that allows free displacement of the blade. The flexible-hub design was tested up to . Rotor integrity was preserved, but local blade cracking occurred. The sliding-blade design was successfully tested up to for over 1 hour at a tip speed of with no issue. Tensile loading at the ceramic/metallic interfaces remains the key challenge to address. Reducing friction should overcome blade cracking and allow the proposed ICT to reach the targeted temperature of and tip speed of .

Effect of pitch angle on power and hydrodynamics of a vertical axis turbine

The use of vertical-axis turbines in marine-current applications for electric energy generation is still in early developments, and one of the key factors for assessing the applicability of such technology is the power coefficient. To contribute towards the highly competitive market of renewable energy conversions, the turbine system requires good outcomes in terms of energy yield. In this scenario, one of the main challenges regarding the design process to improve the blade performance is to find the best trade-off between the maximization of the power output and the minimization of the structural loadings.In the current work, the influence of blade pitch angles on the hydrodynamics of a vertical-axis five-blade water turbine has been studied. The pitch angles from −5° to +5° were investigated using Computational Fluid Dynamics (CFD). The simulations were validated against experimental data for the power coefficient collected in a river. Overall, a good agreement was found in terms of computed power between simulations and experiments for a wide range of tip speed ratios. The CFD model was proven to be suitable for exploratory analyses and an optimized design was found, providing a 2.3% higher power coefficient by adopting a pitch angle of +2° compared to the zero-referenced pitch angle. Besides validating with the experiment, the CFD simulations were compared with the results of a vortex model. The effect of different pitch angles on the performance prediction and on the blade and turbine loadings was also discussed. It is becoming vital to develop an understanding of the complex interaction of vertical-axis turbines, especially in tidal-current areas where there is a lack of detailed experimental data.

Estimation of blade loads for a variable pitch vertical axis wind turbine from particle image velocimetry

AbstractThis paper presents the flow fields and aerodynamic loading of a two bladed H‐type vertical axis wind turbine with active variable pitch for load and circulation control. Particle Image Velocimetry is used to capture flow fields at six azimuthal positions of the blades during operation, three upwind and three downwind. Flow phenomena such as dynamic stall and tower shadow are captured in the flow fields. The phase‐averaged velocity fields and their time and spatial derivatives are used to calculate the normal and tangential loading at each position for each pitching configuration using the Noca formulation of the flux equations. The results show the effect of load shifting from the upwind to downwind region of the actuator using pitch and the effects of dynamic stall on the blades. The results also provide an unique database for model validation.

Fatigue Damage Monitoring of Wind Turbine Blades by Using the Kalman Filter

Fatigue damage accumulation needs to be monitored for extending the lifetime of horizontal axis wind turbines. To monitor accumulation of fatigue damage, this paper proposes a blade load and fatigue damage monitoring system consisting of physics models coupled with the Kalman filter (KF). The proposed monitoring system estimates bending moment distribution along the blade as a time series from 1 Hz data collected by a supervisory control and data acquisition (SCADA) system and from 20 Hz strain sensor data collected at the blade root. Static load is computed on the basis of blade element and momentum theory from SCADA data, whereas dynamic response of the blade is computed by assuming a mass–spring–damper system. The KF corrects the estimated moment distribution with moment measured at the blade root. The monitoring system is demonstrated and validated by installing it on a 2 MW floating downwind turbine and estimating strain and fatigue damage at the medium span position of the blades, where a strain sensor is installed. The validation results show that strain wave forms and fatigue damage estimated by the monitoring system with the KF are consistent with those computed from the strain measurement with sufficient accuracy for structural health monitoring.

Прогнозирование объема каверн на вращающихся лопастях и масштабные эффекты

Object and purpose of research. Pressure pulsations induced by cavitating blades substantially contribute to flowinduced loads and amplify structural vibration. These pulsations depend on oscillation of the volume of cavities over blades. Prediction of them usually involves model tests and there are three kinds of scale effects influencing the cavity volumes. The first one is associated with the non-uniform inflows. The second one is associated with the combined influence of the blade boundary layer and surface tension on the cavity surface. The third one is associated with the cavity buoyancy. Materials and methods. Because of complexity of blade flows, a qualitative analysis of similar unsteady non-uniform flows around 3D hydrofoils is useful. This paper presents such an analysis for a hydrofoil with the sections copied from a marine propeller blade. The inflows correspond to the wakes of a ship and of her model. Computations carried out using an analysis of viscous-inviscid interaction. Main results. The qualitative explanation of observed trends and scale effects is obtained due to this analysis. In particular, the role of pressure side cavitation in full scale conditions is pointed out. Conclusion. The difference of model and ship wakes results in the substantial difference in blade section angles of attack at the same blade loading. Therefore, in model tests the suction side cavitation is more extensive, whereas the pressure side cavitation may not appear, though it exists on full-scale ship propeller blade. This substantial scale effect has been usually out of previous considerations.

Centrifugal pump performance enhancement: Effect of splitter blade and optimization

The shape of impeller blades of a centrifugal pump affects the best efficiency point (BEP), and splitter blades improve the pump performance at BEP. In this work, multiple parameters such as number of blades, length of splitter blade, splitter blade angle at hub, and wrap angle were modified to maximize head and minimize input power. The problem was solved by a numerical and experimental approach. Initially, an impeller was designed and tested in a laboratory setup. The same impeller was simulated in a computational fluid dynamics (CFD) solver, checked the accuracy of the CFD results, optimized by an in-house surrogate-based optimization code and finally the optimal designed manufactured and tested again. The mix and match of the splitter blade with the other parameters improved the pump performance i.e. head by 8.2% and overall efficiency by 3%. The improvement was due to the reduction in pressure fluctuations and uniform blade loading throughout the impeller blade span.

Hub clearance effect in the design space of the cantilevered stator embedded in a 4-stage low-speed research compressor

This paper focuses on the effect of hub clearance in the design space of the highly loaded cantilevered stator. The embedded 1.5 stages of a low-speed research compressor (LSRC) were conducted with Unsteady Reynolds Average Navier-Stokes (URANS) numerical investigation, and the cantilevered stator adopts positive bowed and fore-sweep three-dimensional design. The research details that with the hub clearance increasing from 1.1% to 4.5% span, the loss coefficient and the total leakage momentum of the cantilevered stator correspond to the change of the blade loading near the hub. When designing the inlet metal angle of the rotor downstream the cantilevered stator, emphasis should be given to considering the inter-stage matching below 15% span. The mixing of leakage flow in 1.1% span clearance and 2.5% span clearance is basically completed in the S3 passage, but the mixing of leakage flow in 3.5% span clearance and 4.5% span clearance is still relatively strong downstream of S3. When calculating the relative entropy variation based on Denton’s mixing model, attention should be paid to the relationship between the leakage flow velocity affected by the hub gap and the mainstream velocity, as well as whether the mixing has been completed in the blade passage.

Cauchy type nonlinear inverse problem in a two-layer area

PurposeTo reduce the heat load of a gas turbine blade, its surface is covered with an outer layer of ceramics with high thermal resistance. The purpose of this paper is the selection of ceramics with such a low heat conduction coefficient and thickness, so that the permissible metal temperature is not exceeded on the metal-ceramics interface due to the loss ofmechanical properties.Design/methodology/approachTherefore, for given temperature changes over time on the metal-ceramics interface, temperature changes over time on the inner side of the blade and the assumed initial temperature, the temperature change over time on the outer surface of the ceramics should be determined. The problem presented in this way is a Cauchy type problem. When analyzing the problem, it is taken into account that thermophysical properties of metal and ceramics may depend on temperature. Due to the thin layer of ceramics in relation to the wall thickness, the problem is considered in the area in the flat layer. Thus, a one-dimensional non-stationary heat flow is considered.FindingsThe range of stability of the Cauchy problem as a function of time step, thickness of ceramics and thermophysical properties of metal and ceramics are examined. The numerical computations also involved the influence of disturbances in the temperature on metal-ceramics interface on the solution to the inverse problem.Practical implicationsThe computational model can be used to analyze the heat flow in gas turbine blades with thermal barrier.Originality/valueA number of inverse problems of the type considered in the paper are presented in the literature. Inverse problems, especially those Cauchy-type, are ill-conditioned numerically, which means that a small change in the inputs may result in significant errors of the solution. In such a case, regularization of the inverse problem is needed. However, the Cauchy problem presented in the paper does not require regularization.

MULTIDISCIPLINARY DESIGN OPTIMIZATION OF A LOW-NOISE AND EFFICIENT NEXT-GENERATION AERO-ENGINE FAN

Abstract Due to the increasing bypass ratios of modern engines, the fan stage is increasingly becoming the dominant source of engine noise. Accordingly, it is becoming more and more important to develop not only efficient but also quiet fan stages. In this paper the noise emission of a fan for an aero-engine with bypass ratio of 19 is reduced within a multidisciplinary design optimization (MDO) by means of a hybrid noise prediction method while at the same time optimizing the aerodynamic efficiency. The aerodynamic performance of each configuration in the optimization is evaluated by stationary Reynolds-Averaged Navier- Stokes (RANS) simulations. These stationary flow simulations are also used to extract the aerodynamic excitation sources for the analytical fan noise prediction. The resulting large database of the optimization provides new insights into which extent an MDO can contribute to the design of both quiet and efficient fan stages. In addition to that the hybrid approach of numerical flow solutions and analytical description of the noise sources enables to understand the noise reduction mechanisms. In particular, the influence of rotor blade loading on the aerodynamic efficiency and the noise sources as well as the potential of configurations with a comparatively low number of outlet guide vanes (OGV) is explored.