Investigation of a Novel Turbine Housing to Produce a Non-Uniform Spanwise Flow Field at the Inlet to a Mixed Flow Turbine and Provide Variable Geometry Capabilities

Automotive engine downsizing has placed an increased focus on the ability of the turbocharger to provide adequate boost levels across the full engine operating rage. To achieve the desired levels of turbocharger performance the turbine must be capable of operating effectively at the intended design point and also at off-design conditions. Mixed flow turbines (MFTs) provide a potential method to improve performance at off-design conditions and during transient engine operation. A unique feature of a MFT is the spanwise variation of incidence angle at the rotor leading edge. This results in additional flow separation from the blade suction surface near the hub under a wide range of operating conditions. The flow separation generates additional loss and has a detrimental impact on turbine performance. A novel design of turbine volute similar to a conventional twin-entry turbine volute was examined. The novel turbine volutes were designed to produce a spanwise variation in flow conditions at the rotor inlet. The primary objective was to reduce the incidence angle and increase the mass flow rate at the hub side of the passage relative to the shroud side, as it has previously been identified that this can be beneficial for MFT performance. A number of different volute geometries were examined by numerical analysis to determine the impact of key parameters on turbine performance. The results indicated that generating a suitable spanwise flow distribution could produce a moderate improvement in turbine efficiency at off-design operating conditions. The novel volute design also provided a means of achieving a degree of variable geometry operation to further improve off-design performance. Turbine performance was examined under the variable geometry operation and an improvement in turbine power output at low speed, off-design conditions was achieved. This was analogous to operating with a conventional pivoting vane variable geometry system and had the potential to benefit performance during transient engine operation.

Effect of Winglets on Improving Wind Turbine Performance

Indonesia, with the longest coastline in the world, has enormous potential to develop large-scale wind energy. In wind turbines, the formation of a wake behind the wind turbine can reduce efficiency. It is estimated that the formation of a vortex tip behind the wind turbine blade can be reduced by adding a winglet. The main function of winglets attached to the blade is to reduce the effect of the wingtip vortices which are generated due to 3D spanwise flow that occurs because of the pressure non- equalization between the upper and lower blade surfaces. This paper aims to summarize the results of research on the effect of adding winglets to wind turbines.

The Effect of Blade Count on Body Force Model Performance for Axial Fans

Body force models enable inexpensive numerical simulations of turbomachinery. The approach replaces the blades with sources of momentum/energy. Such models capture a “smeared out” version of the blades' effect on the flow, reducing computational cost. The body force model used in this paper has been widely used in aircraft engine applications. Its implementation for low speed, low solidity (few blades) turbomachines, such as automotive cooling fans, enables predictions of cooling flows and component temperatures without calibrated fan curves. Automotive cooling fans tend to have less than 10 blades, which is approximately 50% of blade counts for modern jet engine fans. The effect this has on the body force model predictions is unknown and the objective of this paper is to quantify how varying blade count affects the accuracy of the predictions for both uniform and non-uniform inflow. The key findings are that reductions in blade metal blockage combined with spanwise flow redistribution drives the body force model to more accurately predict work coefficient as the blade count decreases, and that reducing the number of blades is found to have negligible impacts on upstream influence and distortion transfer in non-uniform inflow until extremely low blade counts (such as 2) are applied.

The superposition of a rotating wake with the atmospheric Ekman spiral

<p align="justify"><span>Stably stratified atmospheric boundary layers are often characterized by a veering wind profile, in which the wind direction changes clockwise (counterclockwise) with height in the Northern Hemisphere (Southern Hemisphere). Wind-turbine wakes respond to this veer in the incoming wind by stretching from a circular shape into an ellipsoid. Englberger, Dörnbrack and Lundquist (2020) investigate the relationship between this stretching and the direction of the turbine rotation by means of large-eddy simulations </span><span>(LESs)</span>.</p><p align="justify"><span>The basic physics underlying the interaction process of a rotating </span><span>wake</span><span> with a veering inflow can be described with the superposition of a Rankine vortex as representation of the wind-turbine </span><span>wake</span><span> with the characteristic </span><span>hemispheric-dependent </span><span>nighttime Ekman spiral of the atmospheric wind. </span><span>In dependence of the rotational direction </span><span>an</span><span>d</span><span> the hemisphere, this</span><span> superposition results in an amplification of the spanwise flow component if a </span><span>counterclockwise</span><span> rotating </span><span>rotor interacts with a northern hemispheric Ekman spiral </span><span>(</span><span>a clockwise rotating rotor interacts with a southern hemispheric Ekman spiral</span><span>)</span><span>. In case of a clockwise rotating rotor interacting with a northern hemispheric Ekman spiral </span><span>(</span><span>a counterclockwise rotating </span> <span>rotor interacting with a southern hemispheric Ekman spiral</span><span>)</span><span>, the superposition leads to a weakening of the spanwise flow component. In case of no veering inflow, the magnitude of the spanwise flow component is independent of the rotational direction.</span></p><p align="justify"><span>Th</span><span>ese theoretical</span> <span>superposition </span><span>effect</span><span> of the Ekman layer with the wake vortex </span><span>occur in nighttime </span><span>LESs, </span><span>where t</span><span>he rotational direction dependent magintude of the spanwise flow component further impacts the streamwise flow component in the wake. In particular, </span><span>there is a rotational direction dependent difference in </span><span>the </span><span>wake strength, </span><span>the </span><span>extension </span><span>of the wake</span><span>, </span><span>the wake </span><span>width, and </span><span>the wake </span><span>deflection </span><span>angle. </span><span>In more detail, a </span><span>northern hemispheric </span><span>veering wind in combination with a counterclockwise rotating actuator results in a larger streamwise velocity output, a larger spanwise wake width, and a larger wake deflection angle at the same downwind distance in comparison to a clockwise rotating turbine.</span></p><p><span>Englberger, Dörnbrack and Lundquist, 2020, Does the rotational direction of a wind turbine impact the wake in a stably stratified atmospheric boundary layer? </span><span><em>Wind Energ. Sci. </em></span><span><strong>5</strong></span><span>, 1359-1374.</span></p>

The Effect of Blade Count on Body Force Model Performance for Axial Fans

Body force models enable inexpensive numerical simulations of turbomachinery. The approach replaces the blades with sources of momentum/energy. Such models capture a “smeared out” version of the blades’ effect on the flow, reducing computational cost. The body force model used in this paper has been widely used in aircraft engine applications. Its implementation for low speed, low solidity (few blades) turbomachines, such as automotive cooling fans, enables predictions of cooling flows and component temperatures without calibrated fan curves. Automotive cooling fans tend to have less than 10 blades, which is approximately 50% of blade counts for modern jet engine fans. The effect this has on the body force model predictions is unknown and the objective of this paper is to quantify how varying blade count affects the accuracy of the predictions for both uniform and non-uniform inflow. The key findings are that reductions in blade metal blockage combined with spanwise flow redistribution drives the body force model to more accurately predict work coefficient as the blade count decreases, and that reducing the number of blades is found to have negligible impacts on upstream influence and distortion transfer in non-uniform inflow until extremely low blade counts (such as 2) are applied.

Hydrodynamics Around a Deep-Draft Semi-Submersible With Biomimetic Tubercle Corner Design

Leading-edge tubercles have been investigating widely on the performance of foils in the last decade. In this study, the biomimetic tubercle design has been applied to the corner shape on a deep-draft semi-submersible. A numerical study on flow over a deep-draft semi-submersible (DDS) with a biomimetic tubercle corner shape was carried out to investigate the corner shape effects on the overall hydrodynamics and motion responses. The hydrodynamic performance of the biomimetic tubercle corner is compared with a traditional round corner design platform. It is demonstrated that, as the corner shape design changed, the motion responses alter drastically. In addition, the flow patterns were examined to reveal some insights into fluid physics due to the biomimetic tubercle corner design. The comprehensive numerical results showed that the three-dimensional effect, which causes spanwise flow, can be reduced by a continuous spanwise (column-wise) variation of the shear-layer separation points.

Numerical Study on Dynamic-Stall Characteristics of Finite Wing and Rotor

To study the three-dimensional effects on the dynamic-stall characteristics of a rotor blade, the unsteady flowfields of the finite wing and rotor were simulated under dynamic-stall conditions, respectively. Unsteady Reynolds-averaged Navier–Stokes (URANS) equations coupled with a third-order Roe–MUSCL spatial discretization scheme were chosen as the governing equations to predict the three-dimensional flowfields. It is indicated from the simulated results of a finite wing that dynamic stall would be restricted near the wing tip due to the influence of the wing-tip vortex. By comparing the simulated results of the finite wing with the spanwise flow, it is indicated that the spanwise flow would arouse vortex accumulation. Consequently, the dynamic stall is restricted near the wing root and aggravated near the wing tip. By comparing the simulated results of a rotor in forward flight, it is indicated that the dynamic stall of the rotor would be inhibited due to the effects of the spanwise flow and Coriolis force. This work fills the gap regarding the insufficient three-dimensional dynamic stall of a helicopter rotor, and could be used to guide rotor airfoil shape design in the future.

Leading-Edge Vortices: Mechanics and Modeling

The leading-edge vortex (LEV) is known to produce transient high lift in a wide variety of circumstances. The underlying physics of LEV formation, growth, and shedding are explored for a set of canonical wing motions including wing translation, rotation, and pitching. A review of the literature reveals that, while there are many similarities in the LEV physics of these motions, the resulting force histories can be dramatically different. In two-dimensional motions (translation and pitch), the LEV sheds soon after its formation; lift drops as the LEV moves away from the wing. Wing rotation, in contrast, incites a spanwise flow that, through Coriolis tilting, balances the streamwise vorticity fluxes to produce an LEV that remains attached to much of the wing and thus sustains high lift. The state of the art of vortex-based modeling to capture both the flow field and corresponding forces of these motions is reviewed, including closure conditions at the leading edge and approaches for data-driven strategies.

Spanwise flow corrections for tidal turbines

Actuator line computations of two different tidal turbine rotor designs are presented over a range of tip speed ratios. To account for the reduction in blade loading on the outboard sections of these rotor designs, a spanwise flow correction is applied. This spanwise flow correction is a modified version of the correction factor of Shen et al. (Wind Energy 2005; 8: 457-475) which was originally developed for wind turbine rotors at high tip speed ratios. The modified correction is described as ‘directionally dependent’ in that it allows a more aggressive reduction in the tangential (torque producing) direction than the axial (thrust producing) direction and hence allows the sectional force vector to rotate away from the rotor plane (towards the streamwise direction). When using the modified correction factor, the actuator line computations show a significant improvement in the accuracy of prediction of the rotor thrust and torque, when compared to similar actuator line computations that do not allow the sectional force vector to rotate. Furthermore, the rotation of the sectional force vector is attributed to the changing surface pressure distribution on the outboard sections of the blade, which arises from the spanwise flow along the blade. The rotation of the sectional force vector can also be used to explain the reduction in sectional lift coefficient and increase in sectional drag coefficient that has been observed on the outboard blade sections of several rotors in the literature