Passive Grid Research Articles

Effect of Trough Incidence Angle on the Aerodynamic Characteristics of a Biomimetic Leading-Edge Protuberanced (LEP) Wing at Various Turbulence Intensities.

A series of wind tunnel tests were performed to investigate the effect of turbulent inflows on the aerodynamic characteristics of variously modified trough incident leading-edge-protuberanced (LEP) wing configurations at various turbulence intensities. A self-developed passive grid made of parallel arrays of round bars was placed at different locations of the wind tunnel to generate desired turbulence intensity. The aerodynamic forces acting over the trough incidence LEP wing configuration where obtained from surface pressure measurements made over the wing at different turbulence intensities using an MPS4264 Scanivalve simultaneous pressure scanner corresponding to a sampling frequency of 700 Hz. All the test models were tested at a wide range of angles of attack ranging between 0°≤α≤90° at turbulence intensities varying between 5.90% ≤ TI ≤ 10.54%. Results revealed that the time-averaged mean coefficient of lift (CL) increased with the increase in the turbulence intensity associated with smooth stall characteristics rendering the modified LEP test models advantageous. Furthermore, based on the surface pressure coefficients, the underlying dynamics behind the stall delay tendency were discussed. Additionally, attempts were made to statistically quantify the aerodynamic forces using standard deviation at both the pre-stall and the post-stall angles.

Experimental and numerical comparison of aerodynamics for a wind turbine rotor model under turbulent inflow conditions

Computational prediction of aerodynamics for a two-bladed wind turbine rotor model at the profile, blade, and rotor scale are compared to wind tunnel experimental data. Wind tunnel tests are carried out in the large subsonic wind tunnel at the University of Orleans with an instrumented rotor model to obtain power and thrust coefficients, bending moments and pressure chordwise distributions. A passive uniform turbulence grid is used to obtain a turbulence intensity of 3.8% at the front of the rotor. A k − ω SST unsteady Reynolds-averaged Navier-Stockes (URANS) simulation with the ISIS-CFD flow solver is conducted with a fully resolved rotor, with and without automatic grid refinement. The focus of this study is to examine the prediction capabilities of the simulation for various physical variables. The simulation demonstrates a relatively good prediction of power and thrust coefficients compared with experimental data with a maximum scatter of 8.5%. The prediction of the pressure coefficient distribution at three different radial positions is satisfactory, but shows discrepancies when it comes to accurately predicting flow separation and Reynolds effects.

Drag on circular cylinders with porous outer layers in turbulent cross-flow

The effects of free-stream turbulence intensity and porosity on the drag on cylinders with porous outer layers in cross-flow was investigated experimentally. This work is motivated by the need to better model spotting—a forest fire propagation mechanism in which burning branches and other debris (termed firebrands) are transported away from the main fire by the prevailing wind and ignite new fires. Multiple levels of background turbulence were studied by using no grid, passive grids, and an active grid to generate turbulence intensities of 0.4%, 1.7%, 2.7% and 12.4%. The porous char-layer on the outer surface of firebrands was mimicked by wrapping wire meshes (of 10, 20 and 40 pores per cylinder diameter or PPD) around the cylinders, each to three different layer-thickness fractions ( 1/16 , 1/8 and 1/4 ) of the cylinder’s outer diameter. The drag on one smooth cylinder and nine cylinders with porous outer layers was measured for Reynolds numbers in the range 7000–17 000, at the aforementioned four turbulence intensities. The results showed that (i) the free-stream turbulence intensity and PPD of the wire meshes affect the Reynolds number dependence of the drag coefficient; (ii) the drag coefficient increases with free-stream turbulence intensity when it is relatively low (0.4%–2.7%), then decreases at high intensities (12.4%), and this decrease is more pronounced as the PPD increases; (iii) the drag coefficient increases with the thickness of the porous layer, and asymptotes to an effectively constant value after a critical thickness of about 1/8 of the cylinder’s diameter; and iv) the drag coefficient exhibits a non-monotonic dependence on the PPD of the wire mesh. These results demonstrate the importance of accounting for free-stream turbulence intensity and the parameters that characterize the porous outer layers of cylinders when modeling the drag on firebrands, or in other applications in which there is cross flow over cylinders with porous outer surfaces.

Generic Modeling and Control Framework for Power Systems Dominated by Power Converters Connected Through a Passive Transmission and Distribution Grid

Generic Modeling and Control Framework for Power Systems Dominated by Power Converters Connected Through a Passive Transmission and Distribution Grid

Particle Image Velocimetry Measurements in a High-Speed Low-Reynolds Low-Pressure Turbine Cascade

Abstract Particle image velocimetry (PIV) measurements in the blade-to-blade (B2B) plane and cascade outlet plane (COP) of a high-speed low-pressure turbine (LPT) cascade were performed at engine-representative outlet Mach number (0.70–0.95), and Reynolds number (70–120 k) under steady flow conditions. The freestream turbulence characteristics were imposed by means of a passive turbulence grid. The PIV results on the B2B plane were compared against five-hole probe (5HP) and Reynolds-averaged Navier–Stokes (RANS) computations to assess the validity of measurement and simulation techniques in the engine-relevant LPT cascade flows. The PIV captured the wake depth and width measured by the 5HP whereas the RANS displayed an overprediction of the wake Mach number deficit. The 5HP was found to impose sinewave fluctuations of the measured flow angle downstream, around three times higher than PIV. Additionally, PIV estimated turbulence intensity (TI) in the cascade, showing TI decay along a streamline. At the highest Mach number, a peak TI occurred past a shock wave. Measurements of the outlet flow field highlighted a high TI in the secondary flow region whereas high degree of anisotropy (DA) was registered in the boundary of the secondary flow and freestream regions. The contribution of the streamwise fluctuation component was found to be less than the crosswise and radial components in the freestream region. Increasing the cascade outlet Mach number, the contribution of streamwise fluctuation to the DA was observed to decrease.

Preliminary performance assessment from towing tank testing of a horizontal-axis turbine

Following the Norwegian government’s goal to be a ‘low emission society’ by 2050, there is a significant push to develop offshore renewable energy; principally offshore wind, but also wave and tidal stream. The MarinLab towing tank at the Western Norway University of Applied Sciences, Norway is 50 m long with a 3.0×2.2 m section and was inaugurated in 2016 as an educational and research facility, supporting local industry to achieve a low-carbon transition.
 To advance knowledge of aero- or hydrodynamic interaction of future turbines for both wind and tidal stream energy, a model scale test-bed horizontal axis turbine has been developed. This turbine will enable testing of rotor diameters typically in the range of 500-600 mm. The turbine is instrumented with a torque-thrust sensor of 5 Nm/100 N capacity, custom-manufactured by Marin in the Netherlands. The turbine is speed regulated via a 4096 counts angular encoder connected to a 200 W Maxon EC-i brushless motor.
 Before testing new rotor geometries, a benchmarking study is being undertaken with an existing known geometry. The benchmark rotor has diameter, D=700 mm and employs the same NACA 63418 airfoil as Mycek et al. (2014), allowing comparison. Unlike Mycek et al. (2014), the nacelle has a nominal diameter of 90 mm and length 760 mm. The size of the rotor risks exceeding the capacity of the torque sensor, such that maximum tow-speed is limited to 0.8 m/s. The benchmark blades are machined from solid aluminium in a four-axis CNC milling machine, following a method similar to Payne et al. (2017). Due to machining limitations, the minimum trailing edge thickness is specified as 0.2 mm. The final surface finish is achieved by manual polishing, and the final dimensions, quantified using a Hexagon ROMER Absolute laser scanner, are found to be within ±0.2 mm accuracy. Future blade sets will typically have a smaller diameter, allowing for 3D printing and consistency of surface finish.
 A blade-element momentum model has been run with Prandtl tip and hub losses and 0° pitch (Fig. I). Lift and drag coefficients were calculated for a range of chord Reynolds numbers using XFOIL, for angles of attack between -5 to 16° and extrapolated to ±180° with Viterna’s method. Due to difficulties in estimating laminar-turbulent transition around critical Reynolds numbers, there is uncertainty in the XFOIL coefficients. At peak TSR, the chord-based Reynolds number is approximately 280k at 3/4 span. Curves for both Rec =250k (solid) and 500k (dashed) with Ncrit = 9 are presented, showing a significant drop in performance for lower Reynolds numbers, due to a collapse in Cl/Cd. Initial tests were conducted in near- zero ambient turbulence, though passive turbulence grids are available for future testing. Reasonable agreement on CT is observed when corrected for blockage according to Bahaj (2007), and further assessment will provide results on CP, tower loads and wake recovery.

Economic assessment of integrating fast-charging stations and energy communities in grid planning

Distribution grid companies and distribution system operators (DSOs) still mostly follow a traditional framework for grid planning. Such frameworks have so far served DSOs well in the economic assessment and cost–benefit analysis of passive measures, such as grid reinforcement. However, the development towards active distribution grids requires DSOs to also be able to assess an extended set of active measures. To this aim, this paper extends and implements a general planning framework for active distribution grids that builds upon the well-proven traditional framework. The methodology integrated in the framework includes: (1) decoupled models for (i) operation with active measures and (ii) optimal grid investment, and (2) methods for economic assessment considering active measures from both (i) a DSO cost–benefit analysis perspective and (ii) a willingness-to-pay perspective. In this paper, operational models are integrated for two examples of active measures, namely the use of fast-charging stations (FCS) and local energy communities (LEC). The methodology is demonstrated in a long-term grid planning case study for a realistic Norwegian medium voltage distribution system. For this case, grid planning with FCS as an active measure reduces the present value of grid investment costs by 70% compared with a passive grid planning strategy. The results also demonstrate how the methodology can be used in negotiating the price of active measures between the DSO and distribution system actors such as LEC and FCS operators.

Experimental investigation on turbulence effects on unsteady aerodynamics performances of two horizontally placed small-size UAV rotors

Wind turbulent disturbance is one of the critical challenges to flying unmanned aerial vehicles (UAVs); especially when the size, weight, and power on board such aircraft are limited. Therefore, to shed light on such turbulent wind effects on UAVs' aerodynamic performances, wind tunnel experiments were conducted on the single- and multi-rotor configurations by varying the turbulence intensity up to 15%, while setting the wind velocity at 5 m/s. The turbulent disturbances were generated inside the wind tunnel using two different passive grids. One is with 29% blockage, and the other is 49%. As the single-rotor experimental tests were conducted, the onset turbulence was found to give rise to a significant change in thrust and the power coefficient in the presence of a lower revolution per minute (rpm). However, at higher rpm, only the wind effect is observed to be the dominant contributor to the aerodynamic performance. Additionally, three different rotor spacings are experimentally examined to measure the propeller wake interactions at the same velocity and different onset turbulence intensities. It was experimentally found that a significant wake interaction occurs between 0.5 D (diameter) and 1.25 D below the propellers, depending on the rotor spacing and the flow conditions. The present work opens up an experimental approach to examine the unsteady aerodynamic performance of multi-rotor UAVs in the presence of wind disturbances, i.e. at different turbulence intensities.

Reducing honeycomb-generated turbulence with a passive grid

Honeycombs are widely used to laminarize fluid streams by inhibiting the lateral components of the fluctuating velocity. However, they also produce additional turbulence by themselves due to the formation of large-scale instabilities and the breakup of the individual velocity profiles stemming from the honeycomb cells. In the present research, we use 2D-planar particle image velocimetry to study how honeycomb-generated turbulence is affected by a downstream grid. It is found that placing a grid near the honeycomb discharge drastically enhances flow uniformity by separating the strong jets stemming from the individual honeycomb cells into many smaller jets that are much more rapidly dissipated. The results show that using a grid reduces the integral length scale by up to a factor 10, and the axial and lateral energy spectra reveal that the grid primarily limits the energy contained in eddies with lower wave numbers. Furthermore, the grid can reduce the magnitude of peak turbulence intensity by as much as 95% and leads to a large reduction of the correlation length, as long as it is positioned upstream of the onset of the large-scale honeycomb-induced instabilities. A downstream grid is highly beneficial for both a laminar and turbulent honeycomb discharge and is most effective when there is a slight offset between the grid and honeycomb. Even though longer honeycombs generally produce more turbulence than short ones due to the larger length-scale of the shear layers, these effects are almost entirely decoupled when using a honeycomb-grid combination. Finally, a honeycomb-grid combination effectively inhibits both axial and lateral turbulence.Graphic abstract

Experimental analysis of a propeller noise in turbulent flow

This paper presents a comprehensive experimental aeroacoustic investigation of a propeller under turbulence ingestion. Two turbulence-generating passive grids were utilized to quantify the effect of turbulence intensity on the aeroacoustic characteristics of the propeller. A two-component hot-wire anemometry was employed to study the flow field. The flow field results demonstrate a substantial increase in fluctuating velocity components in both axial and radial directions, concentrated at the mid-span of the blade and near the tip, respectively. Energy spectral analysis in the vicinity of the propeller blade shows significantly higher broadband energy levels with multiple haystacking peaks at the harmonics of the blade passage frequency. Far-field noise and load measurement results show that turbulence ingestion has a strong effect on the aerodynamic loading and acoustic response at the blade passage frequency. The directivity of noise radiation at low frequency shows a significant tonal noise contribution. Meanwhile, broadband noise radiation is more dominant at a higher range of frequency, especially when the propeller is operated with turbulence ingestion and at higher advance ratio settings. The far-field noise results revealed the haystacking trends in the low frequency domain of the spectra and are most significant for propellers operating in turbulent inflows.

The effects of a passive Bi-Polar Grid (BPG) on Ion Back-Flow (IBF) and resolution

Time Projection Chambers (TPC)s are excellent tracking detectors for high multiplicity events and can intrinsically be high-rate, but are limited by the ions created in their avalanche stage. GEMs and Micromegas can reduce IBF through their geometry and E͐-field ratios, but these can lead to gain fluctuations and still leave IBF as the dominant source of space charge. An active BPG can block all IBF ions, but their slow drift speed creates too much dead time. A passive BPG will overcome this limitation by using an external B͐-field to allow the electrons to pass through while still blocking all ions. Since the grid changes the electron's trajectory, a loss of resolution will occur. The trajectory is shifted symmetrically along the wires so the wire alignment with respect to the detection pads is a specific question not studied before. We present completed IBF analysis from data collected at Weizmann Institute of Science (WIS), along with an intro to our test on wire resolution.

Selective Harmonic Voltage Control for STATCOMs in Wind Power Plants

This paper proposes a selective harmonic voltage control approach for the static synchronous compensator (STATCOM) deployed in wind power plants (WPPs). The method enables STATCOM to mitigate voltage harmonics at the point of interconnection of WPP without using the high-voltage sensor. Further, a passivity-based design of the proposed control method is developed to eliminate the negative resistances around the concerned harmonic components, which allows robust harmonic voltage damping under the different passive grid impedances. The effectiveness of the approach is elaborated by theoretical analysis and validated by electromagnetic simulations.

117 Allocation of Therapist Time: Mobilization of CFU’s in Hand w/Burn Injury

Abstract Introduction Movement of the hands and digits are used to perform communication and activities for IADL’s and competitive employment. Following a second or third degree to the hand(s), there is a potential for the development of burn scar contracture(s) (BSC), which decreases hand skills creating the potential for decreased quality of life. The ABA data base identifies that 70% of burns are sustained to the upper torso, UE, hands. One ABA verified burn center created a study to identify the time required for the burn therapist to elongate hand CFU’s to pre-burn movement. Methods The one-year retrospective study included unilateral and bilateral hand burns with LOS of 2 days or greater or had an outpatient OT session within one week of the burn. Co-author created the Passive Motion Scoring Grid (PMSG), using a number score with higher number indicating greater passive movement. Education was provided to the OT’s to complete the PMSG at the beginning and end of each hand CFU elongation session. Otherwise, there was no change in the OT burn hand therapy treatment. The study included (5) OT’s with mean of 6 years of experience (3-46). Results There were 50 patients, average age was 48.91 years with majority male and African American. All burns were secondary to thermal with burns of 2nd and 3rd degree. There were 33 unilateral hand burns with an average TBSA of 7.02% and 17 patients sustained bilateral hand burns with an average TBSA of 21.3%. Unilateral hand burns had an average number of CFU’s of 39.4 (11-68) and hand CFU’s accounted for 87.1% of the CFU’s. Average number of CFU’s in bilateral hand burns was 90.3 (8-196) with hand CFU’s accounting of 83.4% of the CFU’s. A total of 539 OT sessions were provided to those with unilateral hand burns with an average of 18 OT sessions (3-36). Bilateral hand burns received a total of 487 OT sessions with average of 24.4 OT sessions (4-67) Therapist time for hand CFU elongation to pre-burn status: unilateral hand burns, 43.5 minutes (SD=24.7) and bilateral hand burns was 53.5 minutes (SD=32.2). The minutes only reflect CFU elongation not the entire therapy time. Conclusions Hand burns result in a small number for TBSA, however it results in a greater number of CFU’s than other body locati8ons. The greater number of CFU’s involved, indicates greater potential for development of BSC. At the completion of the burn OT therapy, no patient exhibited BSC. Providing education and information to funding sources regarding CFU’s in hand burns, equating that to potential BSC development and time required for therapist direct hands-on techniques to obtain pre-burn movement can positively influence authorization for therapy. Applicability of Research to Practice Can assist with allocating therapist time with hand burns. Can positively influence funding authorization for therapy.

Give a little to get a little: A DER Bill of Rights and Responsibilities provides the social license for participation and control in DER-dominated grids - an Australian example

When distributed solar photovoltaic systems (PV) provide the majority of supply in electricity grids, system operators and network service providers require increased control of customer-owned assets to maintain system security, reliability and equity. Several programs of reform for distributed energy resources (DER) in Australia, USA and Europe have emphasised the importance of placing customers at the centre of any energy transition, but this has occurred against a haphazard backdrop of proposed solar export taxes, decreasing feed-in tariffs, time-varying export incentives and updated inverter standards. Absent is a conversation of how the social contract of connecting to the electricity grid is evolving beyond the passive expectation of electricity supply of the 19th and 20th centuries to a two-way engagement that must support fairness for both DER-owners and non-owners in grids that are at times dominated by DER. This paper proposes a first attempt at a ‘DER Bill of Rights and Responsibilities’ to provide a template for this required social-license, distinguishing between passive grid participation (passive loads, traditional use, PV self-consumption) and active grid participation (grid interaction for remuneration). Guiding principles of fairness are presented with practical definitions for implementation, referencing existing instruments including inverter standards, network connection agreements, reliability standards, and central ancillary service markets. The intent is that clarity on rights to self-consumption and passive participation will support customer trust in the responsibilities for active DER integration and control. We highlight how proposed rights are already being breached regularly in Australia, as an example jurisdiction, before outlining a pathway to enshrine them for a DER-dominated future with broad sector endorsement. These questions are critical for Australia to address now; other jurisdictions will likely be required to do so in the near future.

Evaluating the effective resolution of enhanced resolution SMAP brightness temperature image products

The MEaSUREs Calibrated Enhanced-Resolution Passive Microwave Daily Equal-Area Scalable Earth Grid 2.0 Brightness Temperature (CETB) Earth System Data Record (ESDR) includes conventional- and enhanced-resolution radiometer brightness temperature (TB) images on standard, compatible grids from calibrated satellite radiometer measurements collected over a multi-decade period. Recently, the CETB team processed the first 4 years of enhanced resolution Soil Moisture Active Passive (SMAP) L-band (1.41 GHz) radiometer TB images. The CETB processing employs the radiometer form of the Scatterometer Image Reconstruction (rSIR) algorithm to create enhanced resolution images, which are posted on fine resolution grids. In this paper, we evaluate the effective resolution of the SMAP TB image products using coastline and island crossings. We similarly evaluate the effective resolution of the SMAP L1C_TB_E enhanced resolution product that is based on Backus-Gilbert processing. We present a comparison of the spatial resolution of the rSIR and L1C_TB_E enhanced resolution products with conventionally-processed (gridded) SMAP data. We find that the effective resolution of daily CETB rSIR SMAP TB images is slightly finer than that of L1C_TB_E and about 30% finer than conventionally processed data.

Blackstart Capability of Modular Multilevel Converters From Partially-Rated Integrated Energy Storage

This paper discusses blackstart provision enabled by Modular Multilevel Converters (MMC) with integrated partially-rated Energy Storage (ES) systems. It is demonstrated that ES units integrated in an MMC for ancillary service provision can be utilised to energise the auxiliary power supply electronics of the submodules (SMs), fully charge the converter capacitors, and establish voltage at the ac and dc terminals. This feature can prove especially useful during the converter start-up phase in passive grids or following a post-fault disconnection event. For an MMC with integrated ES, the added functionality of charging the converter capacitors and starting-up the adjacent networks requires no additional infrastructure – only an updated control scheme. The charging algorithm goes through successive steps: ES-SM charging, <styled-content style="color:black" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">activation of the Auxiliary Power Supplies in the SMs</styled-content> , active charging of all SMs, <styled-content style="color:black" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">and finally,</styled-content> connection to the grid. The effectiveness of the method is confirmed by simulation results where a fully disconnected MMC charges nominally within 2 seconds, and connects to <styled-content style="color:black" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a passive</styled-content> ac network. <styled-content style="color:black" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">By using a grid forming control scheme, the converter ramps up the voltage at the ac terminals and supplies 5% of active and reactive power with only 4% of ES-SMs per stack.</styled-content>

On the generation of full-scale urban pedestrian level wind in the wind tunnel using passive and active turbulence generators

The utilization of outdoor spaces is affected by their thermal environment. Wind, which determines the convective and evaporative heat loss from the human body, is one of the most influencing factors of thermal comfort. In the prevailing outdoor thermal comfort models, the convective heat transfer coefficients were pre-measured on a thermal manikin in a wind tunnel, where the wind speed was mostly stable. However, field measurements suggested that a typical outdoor wind process over complex terrains, like urban landscapes, are generally non-stationary. There is no experimental data on how the misrepresentation of wind may affect the convective heat transfer prediction for outdoor thermal comfort prediction. This study simulates urban pedestrian-level wind patterns in a wind tunnel by employing active and passive turbulence generators. Results show the turbulence scale through an active gust generator is approximately one to two orders of magnitude larger than the turbulence scale through a passive grid system. The eddy length scale can be adjusted through the rotation speed of the shutters. This opens the possibility of performing studies on measuring convective heat transfer coefficient under unsteady wind conditions, similar to the real outdoor environments.

Vibration control of an optical arm

Several nonlinear treatments of piezoelectric voltages have been studied and developed. These techniques greatly improve the switching capabilities of piezoelectric materials. There are active and passive vibration control techniques: Passive technology involves connecting piezoelectric elements to a passive grid; and active technology requires a bulky system that contains at least a sensor, a controller, and a feedback actuator. In addition, control units and actuators require external power supplies and amplifiers. In addition, control units and actuators require external power supplies and amplifiers. SSD (Synchronous Switch Damping) technology allows optimal management of energy transfer in multiphysical couplings, especially electromechanical couplings created by piezoelectric elements. Based on nonlinear manipulation of the voltage of active elements embedded in the host structure, they greatly increase the extracted mechanical energy, which is then converted into electrical energy. Two main areas can benefit from this optimization: vibration control (SSD) technology, because more energy is extracted from the structure to minimize its energy vibration, and energy harvesting (SSH) technology, because the harvested electrical energy becomes sufficient to supply low consumption electronic circuits. This work focuses on vibration control and energy harvesting using embedded piezoelectric elements. First, the SSD principle applied to piezoelectric materials is introduced. Then, a summary is presented of the work consisting on estimating the attenuation obtained on the vibrations of an optical arm by non-linear SSD techniques.

The effect of leading edge porosity on airfoil turbulence interaction noise.

Airfoil turbulence interaction noise and the flow field up to and over the porous leading edge is experimentally studied. The porous leading edges were of the same base triply periodic minimal surface structure with varying porosity to enable us to understand how the porosity, permeability, and pore size affect the generated turbulence interaction noise. The turbulent flow was generated by means of a passive turbulence grid that does not affect the normal background noise of the wind tunnel. Far-field noise results were obtained from a polar microphone array to assess the directivity of the sound as well as the narrowband frequency contributions. Far-field noise results demonstrate that increasing porosity reduces the turbulence interaction noise over low-to-mid frequencies, with a penalty of a high frequency noise increase. Flow measurement results indicate hydrodynamic penetration of the flow into the porous structure at the leading edge. Furthermore, the two-point correlation analysis of the velocity fluctuations approaching the leading edge shows that the turbulent structures approaching the solid leading edge appear to deform into more two-dimensional structures, whereas in the case of the porous leading edge, the turbulent structures appear to retain a strong spanwise coherence up to the point of hydrodynamic penetration.

Coordinated Control of Hybrid DERs Enabled Grid-Interactive Residential PCM With Hybrid Bus Layout

This article proposes a multi-terminal grid interactive power conditioning module (PCM) for integration of hybrid distributed energy resources (DERs) within single phase residential premises, along with the Energy Storage Stacks (ESSs). The PCM also features hybrid bus layouts with medium-low voltage dc (MVdc) and low voltage dc (LVdc), for dc load integrations, and ac bus layout for single phase ac loads. The bi-directional MVdc and LVdc bus facilitate the effective power management and bus voltage support. It operates in all grid feeding, forming and supportive modes. The ESSs includes battery for system energy management and the supercapacitor for dc bus stabilization during transient conditions. The coordinated control of the PCM is capable of interfacing multiple DERs, dc/ac loads, and ESS. The controllers in the PCM are self-adaptive to the frequent islanding situations and ensure the system stability with minimum use of sensory feedbacks. The PCM has loop type dc bus feeder to make residential system operative during transient/faulty conditions. Simulation results verify the feasibility of the proposed system in all active and passive grid feeding; and grid forming modes and experimental setup is used to test the performance of the proposed PCM control through a single microcontroller.