Blade Geometry Research Articles

Experimental and Numerical Heat Transfer Investigation of Impingement Jet Nozzle Position in Concave Double-Wall Cooling Structures

In this paper, experimental and numerical study has been carried out to investigate impingement cooling with a row of five circular jets, varied between target positions on a realistic leading edge region of gas turbine blade geometry. Experimental data is collected from a transient thermochromic liquid crystal measurement technique at the target surface. Numerical study was conducted with the geometry using commercial computational fluid dynamics software to analyze the fluid flow. The unique aims of the study are to observe the effects of variation in jet location, and those specific to realistic target and nozzle geometries. Distributions of local and average Nusselt number show that a location targeting the concave surface at 90° demonstrates an overall higher heat transfer coefficient, especially in the stagnation region, and toward the airfoil sides, with significantly fewer swirls. The experiment was performed with the following parameters: distance from nozzle to target of 1.7 to 2.1 jet diameters, pitch between jets of 4.4 jet diameters, and concave target diameter of 8.0 jet diameters. The jet Reynolds number range during this test was 20,000 − 40,000. A standard flat target plate impingement test is also experimentally conducted and compared against existing literature for method validation.

Aerodynamic design and optimization of propellers for multirotor

PurposeThis paper aims to present a methodology of designing a custom propeller for specified needs. The example of propeller design for large unmanned air vehicle (UAV) is considered.Design/methodology/approachStarting from low fidelity Blade Element (BE) methods, the design is obtained using evolutionary algorithm-driven process. Realistic constraints are used, including minimum thickness required for stiffness, as well as manufacturing ones – including leading and trailing edge limits. Hence, the interactions between propellers in hex-rotor configuration, and their influence on structural integrity of the UAV are investigated. Unsteady Reynolds-Averaged Navier–Stokes (URANS) are used to obtain loading on the propeller blades in hover. Optimization of the propeller by designing a problem-specific airfoil using surrogate modeling-driven optimization process is performed.FindingsThe methodology described in the current paper proved to deliver an efficient blade. The optimization approach allowed to further improve the blade efficiency, with power consumption at hover reduced by around 7%.Practical implicationsThe methodology can be generalized to any blade design problem. Depending on the requirements and constraints the result will be different.Originality/valueCurrent work deals with the relatively new class of design problems, where very specific requirements are put on the propellers. Depending on these requirements, the optimum blade geometry may vary significantly.

Attenuation of the Tip-Clearance Flow in a Pump-Jet Propulsor by Thickening and Raking the Tips of Rotor Blades: A Numerical Study

Cavitation inception and radiated noise of the pump-jet propulsor are closely related to the strength of vortical flows existing in the clearance between rotor-blade tips and duct surface, which is ultimately determined by blade geometry close to the tip. A method is proposed for weakening the tip-clearance flow in pump-jet propulsors by increasing section thickness and rake of rotor blades from 95% tip-radius to the tip. The impacts of the proposed tip-modification method are investigated via numerical simulations by solving the Reynolds-Averaged Navier-Stokes equations with the SST k-ω turbulence model. When the rotor-tip geometry is modified reasonably, the open-water performance of the pump-jet propulsor is barely influenced, though the efficiency of rotor decreases due to the reduction in thrust loading and lift-to-drag ratio close to the tip. Due to rotor/stator interactions, the thrust and torque of a rotor blade as well as pressures at the core of tip-leakage vortex (TLV) fluctuate at multiples of rotor shaft frequency times stator blade number. When the rotor tips are modified, the fluctuation amplitudes of thrust and torque are reduced by more than 35%, the formation of TLV is delayed, the strength of TLV is weakened, and the pressure fluctuation amplitudes at TLV core are almost reduced by 50% at dominating frequencies.

Low-Force Shear Blades Developed for High-Strength Coiled Tubing

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 204403, “Development of Low-Force Shear Blades for High-Strength Coiled Tubing,” by Scott Sherman, Nexus Energy Technologies, prepared for the 2021 SPE/ICoTA Virtual Well Intervention Conference, 22–25 March. The paper has not been peer reviewed. As coiled tubing (CT) grades have evolved during the past 20 years and wall thicknesses have increased, the resulting force required to shear coil has more than doubled. An industry need existed to develop a shear blade for blowout preventers (BOPs) that could cut high-strength CT using legacy pressure-control equipment already in use. The paper describes the iterative process of development of a novel shear blade able to cut high-strength CT with 50% of the normal shear force. Objective The objective of the work detailed in the complete paper was to develop a novel CT-shearing system capable of cutting high-strength heavy-wall CT with reduced hydraulic pressures. Considering that CT will continue to evolve in terms of yield strength, the goal of the study was to future-proof BOPs wherever possible to protect customers from the liability of obsolete equipment. The authors write that, ultimately, BOPs will need to cut 175-grade CT strings with a 7-mm wall thickness with 103 MPa of wellbore pressure and less than 17.2 MPa hydraulic pressure. Development Process Initially, the following five options were considered: - Larger-diameter cylinders. This seemingly simple option, which would generate more shear force, was ruled out because the implementation would not be backward-compatible with existing well-control equipment and the larger cylinder volume would result in slower cycle times. - Boosted actuators. These could double shear force while maintaining piston diameter. While this solution is simple, theoretically, these actuators require twice as much hydraulic fluid from the accumulator to function. This results in a closing time that is nearly double that of a nonboosted actuator. - Pressure-balanced actuators. With this option, hydraulic forces would not need to overcome the forces related to wellbore pressure in addition to providing sufficient force to shear CT. These actuators do increase the amount of shear force available to cut CT when used on high-pressure wells. However, they increase complexity, cost, and weight and could result in trapped wellbore fluids within the actuator that could lead to corrosion-related issues. - Increasing hydraulic pressure to a given set of rams using a pressure multiplier for the shear rams or a similar system. This solution was deemed unsuitable because the hydraulics of most BOPs are designed for 150% of their rated pressure. Doubling the hydraulic pressure available to the BOP could damage the hydraulic cylinders and associated actuators, resulting in a catastrophic well-control situation. - Modifying shear blade geometry to reduce the shear force needed to cut CT using existing equipment. This was selected as the most-logical approach because the modified shear blades could be retrofitted into existing BOPs. Furthermore, this solution would not require modification to existing wellsite equipment such as accumulator skids and would not increase the weight or size of the BOP stack.

Effect of boundary layer suction on performance of a 2 MW wind turbine

Fixed geometry of wind turbine blades imposes some limitations on their operation, making them less efficient in off design conditions which is quite common in real operation. In this work, it is shown that flow separation is the main cause of efficiency drop in under rated wind speeds where the pitch regulation system is not effective. To resolve the problem, the boundary layer suction technique is proposed and studied on a MW class wind turbine. It is shown that by creating a narrow slot at the inboard section of the blade and applying different suction intensities, the power coefficient of the rotor can be improved by up to 8.1%. At the same time, the thrust coefficient variation is limited to only 3.8% which is well compensated by structural safety factors.

Unsteady Steam Turbine Optimization Using High-Fidelity Computational Fluid Dynamics

Abstract This paper presents the computational methodology and experimental investigations accomplished to enhance the efficiency of a turbine stage by applying non-axisymmetric profiling on the rotor hub wall. The experimental setup was a two-stage axial turbine, which was tested at “LISA” test facility at ETH Zurich. The first stage was considered to create the flow history for the second stage, which was the target of the optimization. The hub cavity of the second stage was designed with large dimensions as a requirement of a steam turbine. The goal was to optimize the interaction of the cavity leakage flow with the rotor passage flow to reduce the losses and increase efficiency. The computational optimization was completed using a genetic algorithm coupled with an artificial neural network on the second stage of the test turbine. Unsteady time-accurate simulations were performed using in-house developed “MULTI3” solver. Besides implementing all geometrical details (such as hub and tip cavities and fully 3D blade geometries) from the experimental setup into the computational model, it was learned that the unsteady upstream effect could not be neglected. A novel approach was introduced using unsteady inlet boundary conditions to consider the multistage effect while reducing the computational cost to half. The importance of this implementation was tested by performing a steady simulation on the optimized geometry. The predicted efficiency gain from steady simulations was 4.5 times smaller (and negligible) compared to the unsteady approach. Excluding the cavity geometry was also assessed in a different simulation setup showing 3.9% over-prediction in the absolute efficiency value. Comprehensive steady and unsteady measurements were performed utilizing pneumatic, fast response aerodynamic probe (FRAP), and fast response entropy probe (FENT) on the baseline and profiled test cases. The end wall profiling was found to be successful in weakening the strength of the hub passage vortex by a 19% reduction in the under-over turning. As a result, the blockage was reduced near the hub region leading to more uniform mass flow distribution along the span. The flow angle deviations at the higher span position were also corrected due to better control of the flow angles. Furthermore, the improvements were confirmed by reductions in entropy, secondary kinetic energy, and pressure unsteadiness. The accurate computational implementations led to an excellent agreement between the predicted and measured efficiency gain.

A Straight-Bladed Vertical-Axis Turbine for Wave Energy Conversion: Effect of Guide-Vane Geometry on Performance

This study proposes a straight-bladed vertical-axis turbine for ocean-wave energy conversion. The aim is to develop a novel air turbine suitable for an oscillating water column in a wave energy plant. To this end, the performances of straight-bladed vertical-axis turbines were investigated for different guide-vane geometries in a wind tunnel experiment. The rotor has four straight blades with an NACA0018 profile, a chord length of 80.5 mm, a pitch diameter of 460 mm, and a blade width of 490 mm. In this study, the guide-vane geometry was varied as arc, semi-arc, and semi-arc with a straight part. Under steady flow conditions, the turbine performance was evaluated by determining the torque, input and flow coefficients, and the turbine efficiency. The semi-arc blade geometry decreased the input coefficient and increased the torque coefficient. Moreover, the semi-arc blade with a straight part improved the starting characteristics of the turbine and its efficiency over a wide range of flow coefficients.

A Quantitative Comparison of Aeroelastic Computations using Flex5 and Actuator Methods in LES

Actuator disc and actuator line techniques are widely used for modelling wind turbines operating in wind farms. These techniques essentially replace the blade geometry with applied body forces, which reduce the resolved length scales significantly and hence the required grid resolution. This work is a verification of the coupling between the flow solver EllipSys3D and the aeroelastic tool Flex5, through a quantitative comparison of coupled actuator line, coupled actuator disc, and standalone Flex5. Steady state performance predictions, instantaneous reaction to turbulence and damage equivalent load analyses all show a very good agreement between the three methods. Differences can be explained primarily by the higher fidelity modelling of the coupled simulations; this is particularly in regard to the influence of blade flexibility, as the actuators deflect and interact with the modelled flow. Additionally, some overpredictions of loading at the blade tip and root below rated velocity for the actuator methods can be attributed to the Gaussian smearing used to apply the body forces.

Influence of blade corrosion on aerodynamic characteristics of a gas turbine

Gas turbine blades, such as nozzle guide vanes and rotor blades, corrode over time and thus deteriorate, becoming thinner and shorter. In the present study, influences of blade corrosion on aerodynamic characteristics were examined numerically. The purposes of this study were to understand the influence of the blade deterioration on aerodynamic characteristics quantitatively under the same conditions with that in a power plant, and to clarify how to detect severe deterioration during gas turbine operation. Blade geometries before and after use were obtained from a real gas turbine using a 3-D scanner. Two parametric CFD simulations were carried out: one simulation was conducted with various turbine expansion ratios and a fixed turbine inlet temperature, and the other was conducted with various inlet temperatures and a fixed expansion ratio. According to the results of both simulations, a change in the throat area of the first-stage nozzle affected the aerodynamic characteristics significantly. The expansion ratio was found to be more useful. Numerical results obtained under actual operating conditions confirmed that the difference in the expansion ratio was about 3% between the new and old blades in the examined gas turbine.

A robust inverse design solver for controlling the potential aggressiveness of cavitating flow on hydrofoil cascades

AbstractThis article presents the development of a new inverse design algorithm capable of generating blade geometries for cavitating cascade flows. With this methodology, we demonstrate the controllability of the pressure distribution in and around the cavity and thereby provide a means to regulate the aggressiveness of blade cavitation phenomena. The solver proposed here uses the Tohoku–Ebara equation of state to model phase change, combined with bespoke preconditioning and multigrid methods designed to handle the system's ill conditioning and cope with the hypersonic flow regime of the mixture, respectively. Blade geometries and the cavitating flow field are calculated simultaneously in a robust and efficient manner, with a blade loading that matches the target distribution. In this article, the accuracy of the cavitating flow solver is first demonstrated for the NACA0015 hydrofoil case and associated experimental data. The inverse design procedure is then applied to a typical axial flow pump cascade: a new blade profile is generated with a topology that successfully reduces the gradient of the pressure jump at cavity closure.

Aerodynamic and Structural Strategies for the Rotor Design of a Wind Turbine Scaled Model

Experimental tests performed in a wind tunnel or in a natural laboratory represent a fundamental research tool to develop floating wind technologies. In order to obtain reliable results, the wind turbine scale model rotor must be designed so to obtain a fluid-structure interaction comparable to the one experienced by a real machine. This implies an aerodynamic design of the 3D blade geometry but, also, a structural project to match the main aeroelastic issues. For natural laboratory models, due to not controlled test conditions, the wind turbine rotor model must be checked also for extreme winds. The present paper will focus on all the strategies adopted to scale a wind turbine blade presenting two studied cases: the first is a 1:75 scale model for wind tunnel applications and the second a 1:15 model for natural laboratory tests.

Experimental investigations and aerodynamic shape optimization of small horizontal-axis wind turbine blades

This study aims to optimize and investigate small horizontal-axis wind turbine blades at low wind speeds. The objective of this study is to explain the design method based on BEM theory for 0.2 m blade rotors with constant, variable, and linear chord with twisted blade geometry. MATLAB and Xfoil programs were used to apply BEM principles on wind turbines with SG6043 airfoil. Numerical and experimental studies were carried out to examine the impact of rotor solidity values from 0.057 to 0.207 and the number of blades from 3 to 7. The experimental blades were developed using a 3D printing additive manufacturing technique. The rotors were investigated in an open wind tunnel at wind speeds ranging from 2 to 8 m/s. The initial investigation range included tip speed ratios from 2 to 8 and angles of attacks from 2° to 20°. Subsequently, these parameters were varied in Matlab and Xfoil software to optimization and investigate the power coefficient, blade geometry, number of blades, and blade pitch angle. It was found that a rotor solidity of 0.055–0.085 displayed better performance.

Redesign of Axial Fan Using Viscous Inverse Design Method Based on Boundary Vorticity Flux Diagnosis

Abstract The inverse design method for turbomachinery can directly acquire a blade geometry with specific aerodynamic parameters, such as pressure loading on the blade surfaces. The difference between the inverse design and direct analysis design is that the management of the flow field is controlled by aerodynamic parameters instead of geometric parameters. Although the inverse design has been studied since the 1940s, it is far from being mature enough in comparison with the analysis method. In this work, the inverse problem method is improved by two aspects: the calculation accuracy and the strategy to determine the pressure loading distribution. The application of a high-quality mesh auto-generation and deformation technique to the inverse design is introduced. The no-slip wall boundary conditions, similar to the analysis model, and high-quality mesh, enable the use of an advanced turbulence model in the inverse design. These methods improve the accuracy of the inverse design. The loading distribution in the inverse design is obtained based on the boundary vorticity flux diagnosis. An axial fan is redesigned as an example of the inverse design method. The internal flow loss analysis based on the entropy production theory verifies the effectiveness of the inverse design used in this study.

Performance assessments and simulations of ROT (radial outflow turbine) for back-pressure turbine generator system

The high pressure steam is regulated by the Pressure-Reducing Valves (PRVs) to suit the various industrial process; however, this, inevitably leads to economic and energy losses. In this study, PRV is replaced by a back-pressure turbine generator comprising a Radial Outflow Turbine (ROT). The structural characteristics of the ROT, such as the easy adjustment of the tip clearance, make it possible to control the steam properties. The steam with selectively reduced pressure (and temperature) can be provided to users. The blade geometry of the ROT is designed using a commercial software. The numerical prediction of the fluid properties is carried out using a real fluid model in ANSYS-CFX. The simulation results are compared with the experimental results obtained under the same off-design conditions. The tip clearance (100, 300 and 500μm) are applied as a parameter to investigate the change of performance and to adjust the properties of the discharged steam. The experimental results show that the maximum electrical power produced at the minimum tip clearance is 12.8 kW, and the temperature and pressure differences tend to decrease with increasing tip clearance. These results demonstrate the potential of the ROT as a PRV and energy recovery device in back-pressure turbines.

Static Analysis of the Last Stage Low Pressure Steam Turbine Blade to Improve Blade twist Angle

Demand for electricity is growing continuously and the production is still based on limited sources of energy, mainly the turbomachinery, which include basically the steam and gas turbines. Turbomachinery is responsible for about 80% of the electricity generated worldwide. A large variety of turbine blade geometries are in use today, however, there is no specific attempt made to compare them based on performance.This paper presents a study on the effect of the twist angle of the steam turbine blade on different choice blade materials. For the study, the aerodynamic and static loading of the 19th stage low pressure turbine blade of Egbin thermal power station was evaluated. Static analysis based on computational fluid dynamics (CFD) was used to simulate the conditions of the turbine blade during normal operating conditions. Alternative materials (such as stainless steel 316, Titanium alloy) and varying twist angles were observed to be showing different forms of results in the simulation on ANSYS. From these, an optimized twist angle was generated using Response Surface Optimization on ANSYS RSO, and the consequent results were discussed.

Review of Specific Performance Parameters of Vertical Wind Turbine Rotors Based on the SAVONIUS Type

Increasing energy demand and environmental regulations around the world provide an adequate framework for developing methods of obtaining energy from renewable sources. Wind force is a resource with a high potential through which green energy can be obtained with no negative impact on the environment. Different turbine typologies have been developed, which can convert the wind force into mechanical and electrical energy through turbine rotational motion. Starting from the classic vertical-axis SAVONIUS rotor model, other models have been designed, which, according to the numerical studies and experimental test results, show higher performance parameters in operation. Such models present specific rotor blade geometries to achieve better operational results in terms of shaft torque and generated power. There are multiple research results from numerical analysis on virtual models or experimental tests that use rotor models in different constructive configurations aiming to improve operation performance. These research activities are related to the rotor blade number, the aspect and overlap ratio values, the blade profile geometry modification, the use of end plates connected to the rotor blades, curtain mounting solutions for directing the air flow on the active blade alone, and rotor constructive variants with deformable blades during operation. Some of the results obtained from the mentioned research activities are shown in this review for special rotor configurations whose performance results in terms of torque or power values are compared to the classical SAVONIUS model.

Model mikroturbiny wiatrowej o regulowanym kącie ustawienia łopat

The article presents the results of research into the operation of a model of a wind micropower plant with a variable blade angle. The research was carried out on a miniature model of a measuring stand built for the purpose of carrying out work on pre-developed projects of wind micro power plants. The stand allows to carry out measurements related to the selection of the optimal propeller geometry, as well as the development and testing of algorithms for optimal control of the micropower plant. The physical basics of wind turbine operation and the methods of its optimal control are presented. The results of the performed measurements for the selected propeller blade geometry with the possibility of changing its setting angle are presented. A DC generator with a load with a non-linear characteristic in the form of a Li-Po battery cell was used. The results of operation of a simple MPPT control algorithm are presented. The lack of optimal control systems for the operation of micropower plants is dictated by the general belief that the costs of its production are high in relation to the possible improvement of the efficiency of micropower plants. Moreover, the practical methods of controlling larger wind turbines are not optimal for small and very small turbines. The conducted research focused on determining the possibility of using turbines with variable blade angles depending on its rotational speed. In larger wind farms, changing the blade angle is mainly used to limit the power of the turbine at high wind speeds. In micro wind power plants such solutions are not used for economic reasons. However, the use of a simple mechanism for changing the angle of the blades depending on the rotational speed of the propeller can increase the efficiency of the turbine in a wider range of wind speeds. The small dimensions of the research model allow for quick and cheap development of preliminary prototypes of turbine blades thanks to the possibility of using 3D printing technology.

Aerodynamic design of tractor propeller for high-performance distributed electric propulsion aircraft

Aiming to maximize the aerodynamic performance of the Distributed Electric Propulsion (DEP) aircraft, a hybrid design framework which focuses on the aerodynamic performance of the propeller/wing integration has been developed and validated numerically. Variable-fidelity modelling for propeller aerodynamics has been used to achieve computational efficiency with reasonable accuracy. By optimizing the aerodynamic loading distributions on the tractor propeller disk, the induced slipstream is redistributed into a form that is beneficial for the wing downstream, based on which the propeller blade geometry is generated through a rapid inversed design procedure. As compared with the Minimum Induced Loss (MIL) propeller at a specified thrust level, significant improvements of both the lift-to-drag ratio of the wing and the propeller/wing integrated aerodynamic efficiency is achieved, which shows great promise to deliver aerodynamic benefits for the wing within the propeller slipstream without any additional devices.

Effect of optimal slot location on the performance of cascades of blades

Overloaded blades and lower solidities are two main characteristics of modern gas engines to reach lower specific fuel consumption and weight to thrust ratio. Hence, flow optimization methods are employed to maximize the performance. Slot treatment on blades is considered as a potential method to stand against the boundary layer separation for this issue. In the present study, the different locations of passive flow control with the slot along the compressor blade chord are simulated at four angles of attack (α), ranging from 10.93° to 28.93°. The purpose of this study is to discover the underlying reason in obtaining the best slot location, regarding the blade turning angle and total loss coefficient, in every tested inflow angle. Based on the results, the slot jet shows its utmost performance in eliminating the trailing edge separation when it is located upstream of the separation lines in the mid-span. The best slot location is able to improve the turning angle and the total loss coefficient up to 16.41% and 16.47% at 26.93°, respectively. The synthetic slot jet confines the growth of corner vortices and increases the turning angle near end walls up to 4°. In addition, the slot treatment pushes the backflow region over the suction surface up to 10% of the span toward the side walls. The importance of choosing the slot location decreases with an increase in inflow angle. However, the effect of slot locations on the performance in low angles is still considerable. With the tested blade geometry, the slotted profile in locations between 0.5 and 0.8 of axial chord length indicates a promising blade performance either in low or high angles. The slot treatment weakens the flow upstream of its location which is in contradiction with previous investigations. Two separation bubbles near the leading edge in the baseline profile have a greater size of about 2% of the blade chord for the slotted case.

3D Multidisciplinary Automated Design Optimization Toolbox for Wind Turbine Blades

This paper presents two novel automated optimization approaches. The first one proposes a framework to optimize wind turbine blades by integrating multidisciplinary 3D parametric modeling, a physics-based optimization scheme, the Inverse Blade Element Momentum (IBEM) method, and 3D Reynolds-averaged Navier–Stokes (RANS) simulation; the second method introduces a framework combining 3D parametric modeling and an integrated goal-driven optimization together with a 4D Unsteady Reynolds-averaged Navier–Stokes (URANS) solver. In the first approach, the optimization toolbox operates concurrently with the other software packages through scripts. The automated optimization process modifies the parametric model of the blade by decreasing the twist angle and increasing the local angle of attack (AoA) across the blade at locations with lower than maximum 3D lift/drag ratio until a maximum mean lift/drag ratio for the whole blade is found. This process exploits the 3D stall delay, which is often ignored in the regular 2D BEM approach. The second approach focuses on the shape optimization of individual cross-sections where the shape near the trailing edge is adjusted to achieve high power output, using a goal-driven optimization toolbox verified by 4D URANS Computational Fluid Dynamics (CFD) simulation for the whole rotor. The results obtained from the case study indicate that (1) the 4D URANS whole rotor simulation in the second approach generates more accurate results than the 3D RANS single blade simulation with periodic boundary conditions; (2) the second approach of the framework can automatically produce the blade geometry that satisfies the optimization objective, while the first approach is less desirable as the 3D stall delay is not prominent enough to be fruitfully exploited for this particular case study.