Flow Control Capability Research Articles

Investigation of Hybrid Laminar Flow Control Capabilities from the Flight Envelope Perspective

The present work conducts a multifidelity aerodynamic design of a medium-range commercial aircraft wing featuring hybrid laminar flow control (HLFC) technology. The design was performed to investigate the capabilities of the HLFC, considering the entire design flight envelope, low-speed performance requirements, and various potential mission scenarios. A combination of medium-fidelity aerodynamic design tools for laminar flow control using MSES-COCO-LILO, CFD RANS for high-lift cases, the quasi-three-dimensional for database generations, and SUAVE for mission analysis were used to design and assess aircraft’s performance with the HLFC wing. Studies of the design objective demonstrated a conflict between friction and compressibility drag that strongly affects the design objective function and the wing performance at various off-design conditions. A strong dependence of HLFC on flight conditions was observed to indicate technology performance limitations and a tradeoff between airplane emissions, range, and costs. Finally, a comparison of medium- and low-fidelity performance results showed deviations in the design fuel burn of 4%, a minimum possible harmonic range difference of 3%, and direct operating costs of 2%. The outcome suggests the need for better compressibility and parasite drag models for early design stages to accurately model the HLFC technology without introducing complicated methods at the first sizing steps.

Hybrid nanofluids flow over a Riga plate surrounded by a variable porous medium for heat transfer optimization

Enhancing the heat transfer rate in hybrid nanofluids is significantly aided by a porous medium. The nanofluid’s heat transfer to the surrounding medium is more efficient due to the presence of a porous medium. The porous space also provides additional surface contact points for heat exchange and an intricate network of interconnected pores. This article elaborates on the incorporation of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) into water to perform hybrid nanofluids. The flow is considered over a Riga plate surrounded by a variable porous space. Various applications, including thermal management systems, microelectronics cooling, and energy conversion devices, benefit greatly from the study of hybrid nanofluid flow on a Riga plate. The similarity equations of the flow problem are easily tackled with the homotopy analysis method (HAM) built on fundamental homotopy mapping. Furthermore, with the increments in paramount parameters, the skin friction coefficient and heat transfer rate are remarkably meliorated under a higher modified Hartmann number. All reverberations are illustrated in graphs and Tables. From the obtained results it is observed that flow control capabilities are enabled by the variations in permeability in the case of hybrid nanofluids. It is also observed that hybrid nanofluids are more capable to enhance the thermal capabilities of the traditional fluids as compared to the mano nanofluids.

Large eddy simulations (LES) of a three-element high-lift wing: Exploring the active flow control (AFC) capabilities

This study presents an aerodynamic analysis of the 30P30N high-lift three-element wing under varying the angle of attack (α = 5°, 9°, and 23°) at a constant Reynolds number (Rec = 750, 000) by means of large eddy simulations (LES). Baseline results were validated against existing literature, demonstrating good agreement. The increase of the angle of attack entails higher values of lift but also, increased values of drag. At α = 23°, a recirculation area appears above the flap, this being the signature of the stall conditions. This is related to the adverse pressure gradient that develops along the main suction side and the separation of the streamlines in its wake. Actuation strategies using synthetic jets were explored to mitigate this flow separation at this angle of attack, and thus, enhance the efficiency of the wing. Three actuation cases with the jets located on the main wing, on the flap, and on both elements at the same time were investigated. While some improvements are observed with the actuation, particularly in the combined actuation case, the overall wing efficiency was only marginally enhanced. Challenges in achieving significant improvements were attributed to complex flow interactions and the dominance of pressure forces, which affect both the lift and the drag coefficients at the same time.

Aerodynamic performance measurement of a novel variable geometry turbine adjustable guide vane scheme by experimental study

As the key component of new-generation variable cycle engines, the adjustable turbine guide vane's through-flow regulation capability and aerodynamic performance have a significant impact on the performance of the turbine stage and even the core engine. Conventional adjustable guide vanes control the through-flow capability by varying the installation angle and thus inevitably result in a gap clearance, which induces a new source of flow losses. This additional loss can degrade the aerodynamic performance of the variable geometry turbine considerably. Therefore, a novel adjustable guide vane scheme with a rotatable suction surface to regulate the through-flow capability is proposed in this paper and its superiority is verified in a typical small aspect-ratio vane. To this end, a high Mach number annular cascade test rig with high-resolution aerodynamic measurement systems is designed and built to determine the aerodynamic performance of this novel adjustable guide vane as well as a conventional one. The mass flow control capability, the total pressure loss coefficient, the isentropic Mach number at the blade surface, and the static pressure distribution at the endwall are measured for these two schemes, respectively. The flow details and loss mechanisms are also clarified with the aid of CFD. The results show that this novel adjustable guide vane scheme achieves a comparable through-flow control capability with respect to the conventional one, with a total pressure loss reduction of 25%-35% at the measured Mach numbers. The flow details reveal that the novel scheme avoids the large-scale leakage vortex that exists in the conventional scheme and also produces a more uniform exit airflow angle distribution for the downstream rotor.

Efficient congestion management using embedded MVDC-connections between distribution systems

The massive integration of renewable energy generation in distribution systems causes high fluctuations in the power system utilization. At times of peak wind and PV generation, the exceeding power flows to the points of common coupling to the transmission system, adds up and causes grid congestions. Due to a lack of grid extension, these congestions are often addressed by capping of renewable generation. This paper introduces an alternative approach by using the power flow control capability of MVDC-links between two distribution systems to increase the potential power system utilization and therefore reducing the occurrence of congestions and increasing the share of renewable energy generation in the grid. The presented numeric case study of two realistic German 110 kV systems with one 130 MW MVDC-connection shows a significant reduction of the congestion power for grids with high renewable penetration.

On the influence of porous coating thickness and permeability on passive flow and noise control of cylinders

Aeroacoustic studies of porous cylinder coatings, which reduce the vortex shedding noise of cylinders in uniform flow, have received increased attention. To further understand how porous coatings suppress the vortex shedding tone, a numerical and experimental investigation of porous coated cylinders at a Reynolds number of 1.27×105 is presented herein. Two parameters were varied: (1) the ratio of the porous thickness to the bare cylinder diameter, and (2) the airflow resistivity of the porous media. Numerical simulations were performed using the large-eddy simulation approach with the Smagorinsky sub-grid length-scale model, and the Ffowcs-Williams and Hawkings acoustic analogy was used to predict the acoustic far-field pressure field. A numerical investigation of the internal flow field within the porous layer is presented, which provides a better understanding of the influence of the aforementioned parameters on the development of boundary layers within the porous media and the passive flow and noise control capability. Experiments were performed in an aeroacoustic open-jet wind tunnel to validate the acoustic and external flow field results, which typically showed very good agreement with the numerical results. For porous coatings with low airflow resistivity, the thickness of the porous coating, relative to the inner diameter, has a strong influence on passive flow and noise control. Vortex shedding originates from the inner diameter. Conversely, porous coatings with a higher airflow resistivity are less influenced by their thickness, and vortex shedding originates from the outer diameter (porous surface). The complex coupling of these parameters leads to the conclusion that the optimal selection of the thickness and airflow resistivity is typically dependent on the Reynolds number.

Novel Universal Power Electronic Interface for Integration of PV Modules and Battery Energy Storages in Residential DC Microgrids

This paper introduces the novel concept of a highly versatile smart power electronic interface for fast deployment of residential dc microgrids. The proposed approach has bidirectional power flow control capabilities, wide operating voltage range, and high efficiency resulting from the topology morphing control utilization. This enables universal compatibility with the majority of the commercial 60- and 72-cell photovoltaic modules, as well as the efficient charge/discharge control of the 24 V and 48 V battery energy storages using the same hardware platform. The proposed concept features fully autonomous operation where switching between the photovoltaic and battery interfacing modes is automatically done using the input source identification algorithm. Moreover, the proposed universal interface converter employs droop control and solid-state protection, making it fully compatible with the emerging standards and requirements for power electronic systems used in dc microgrid environments. A 350 W prototype was developed and tested in the residential 350 V dc microgrid with droop control to validate the proposed concept experimentally.

Multiport Hybrid DC Circuit Breaker With Current Flow Control for MTDC Grids

The multiterminal dc (MTDC) grid plays an important role in large-scale power transmission and renewable energy integration owing to its excellent performance. However, there are still some problems existing in the MTDC grid, such as difficult fault current interruption and current flow control, which impedes its development. Currently, the mentioned two problems can be separately solved by hybrid dc circuit breaker (HCB) and current flow controller (CFC). However, when configured separately, they are expensive and have large footprints. Therefore, this article proposes a multiport hybrid dc circuit breaker (MHCB) with current flow control capability. The HCBs near the same dc bus are first integrated into a single MHCB and then novel CFCs are embedded into the MHCB to replace the load commutation switches. Compared with the existing MHCBs, the proposed topology shows advantages in the aspects of implementation cost, power loss, and operation speed. The operation principle is analyzed and the basis for parameter design is given in detail. The effectiveness of the proposed topology is verified by extensive simulations and experiments. Besides, the proposed MHCB is compared with the existing solutions.

A Multiport Embedded DC Power Flow Controller for Meshed DC Distribution Grids

Ring and meshed dc distribution grids have attracted increasing interest lately. Their multipoint and multiterminal structure facilitates flexible operational control and reliable power supply across the network. However, the dc grids implemented with existing power converters lack sufficient control freedoms for proper power flow adjustment; therefore, it is necessary to develop additional dc power flow controllers (DCPFCs) to be added to these grids for improved power flow control capability. Specific to multiterminal dc networks built with modular multilevel converters (MMCs), this article proposes an embedded DCPFC (e-DCPFC) directly integrated in the MMC topology. Unlike previously proposed solutions, the e-DCPFC configuration is derived from the conventional MMC and does not need any isolation transformers or external power supply. Its other main features include modular construction, convenience for multiport extension and bidirectional power flow adjustment capability. In this article, the topology, working principle, and the coordinated control strategy for e-DCPFC and its host MMC are elaborated. Experimental results from a lab prototype verify the proposed topology and its performance under typical working conditions.

Improving the resilience of large-scale power systems using distributed static series compensators

Natural disasters such as hurricanes can cause severe damages at the transmission level, resulting in widespread power outages and renewable energy curtailment. To reduce such power outages and renewable curtailment, this study takes advantage of the power flow control capability of distributed static series compensators (DSSC) and proposes a model to optimally deploy DSSC in face of natural disasters. The model is based on stochastic optimization and can determine the optimal locations and quantities of the DSSC modules in power systems considering transmission contingencies. With a high computational efficiency, the model can meet the time frame requirement for DSSC redeployment after natural disasters to improve the resilience of large-scale, real-world power systems. The model was implemented on a modified Texas 2000-bus test system under different conditions, and results show that the proposed model can optimally allocate DSSC to mitigate transmission congestions in both normal operations and emergent situations after natural disasters. By optimally redeploying DSSC using the proposed model after natural disasters, load shedding and renewable energy curtailment can be reduced up to 100% and 90%, respectively, improving the resilience of the power system.

A successive flow direction enforcing algorithm for optimal operation of variable-impedance FACTS devices

This paper presents a novel successive flow direction enforcing (SFDE) algorithm for solving power system operation models with flexible AC transmission system (FACTS) devices. The power flow control capabilities of FACTS devices can improve the utilization of the existing transmission network. However, the added computational complexity of modeling FACTS devices in power system operation models is one of the primary challenges for FACTS deployment. A prominent component is the nonlinearity introduced by variable-impedance FACTS devices to the linear DC power flow equations. According to previous studies, such nonlinearity can be tackled by preassigning the power flow directions on lines equipped with FACTS to restore the linearity of DC power flow equations. However, this method has the issue of converging to suboptimal solutions in some cases, due to suboptimal flow direction assignment. The algorithm presented in this paper can address the issue of suboptimality, while still achieving computational efficiency improvements. Power system operation models with FACTS are solved iteratively with flow directions enforced, and the predetermined flow directions are adjusted successively based on the results of the previous iteration. Simulation studies confirm the effectiveness of the method in converging to the globally optimal solution within a few iterations in almost all practical cases.

A miniaturized 3D printed pressure regulator (µPR) for microfluidic cell culture applications

Well-defined fluid flows are the hallmark feature of microfluidic culture systems and enable precise control over biophysical and biochemical cues at the cellular scale. Microfluidic flow control is generally achieved using displacement-based (e.g., syringe or peristaltic pumps) or pressure-controlled techniques that provide numerous perfusion options, including constant, ramped, and pulsed flows. However, it can be challenging to integrate these large form-factor devices and accompanying peripherals into incubators or other confined environments. In addition, microfluidic culture studies are primarily carried out under constant perfusion conditions and more complex flow capabilities are often unused. Thus, there is a need for a simplified flow control platform that provides standard perfusion capabilities and can be easily integrated into incubated environments. To this end, we introduce a tunable, 3D printed micro pressure regulator (µPR) and show that it can provide robust flow control capabilities when combined with a battery-powered miniature air pump to support microfluidic applications. We detail the design and fabrication of the µPR and: (i) demonstrate a tunable outlet pressure range relevant for microfluidic applications (1–10 kPa), (ii) highlight dynamic control capabilities in a microfluidic network, (iii) and maintain human umbilical vein endothelial cells (HUVECs) in a multi-compartment culture device under continuous perfusion conditions. We anticipate that our 3D printed fabrication approach and open-access designs will enable customized µPRs that can support a broad range of microfluidic applications.

Towards quantum thermal multi-transistor systems: Energy divider formalism

A quantum thermal transistor controls the flow of thermal energy through two of its terminals in response to an external input signal on its third terminal. In recent years, several realizations of thermal transistors combining individual quantum systems have been proposed using temperatures or optical fields as the control signals. The success of the electronic transistor in modern technology partly lies in its ability to combine and make multi-transistor systems with enhanced flow control capability or even wholly different behaviors. Hence, as the next natural step, we investigate the intricacies of building composite systems combining multiple quantum thermal transistors. We identify that the interconnects of thermal transistors play a critical role in these systems by facilitating energy exchange from one transistor to another. By isolating the exact functionality of these interconnects, we develop a simple model that still captures all its essential characteristics. This model shows that directly coupling transistors allows a substantial energy transfer between them only under highly restrictive conditions. We then develop the energy divider formalism where a single properly tuned quantum harmonic oscillator acts as an intermediary between the transistors. We demonstrate that the oscillator mediates a substantial energy exchange under a considerably relaxed set of conditions and illustrate its operating principles through detailed quantum mechanical state analysis. We compare our energy divider based interconnect against the previously developed intermediate bath method and confirm that both ways achieve similar thermal energy flow rates between the transistors over a broad range of operating temperatures. At the same time, replacing an intermediate bath made up of a large number of harmonic oscillators with a single oscillator avoids many of the theoretical and practical limitations of the earlier method. For instance, time-domain simulations show that the energy divider based interconnect responds far faster to an external excitation than the corresponding intermediate bath based system. We believe the energy divider formalism provides valuable insights into the nature of thermal energy transfer within quantum thermal systems.

Dc-MMC for the Interconnection of HVDC Grids With Different Line Topologies

DC-DC converters are needed for the future development of high voltage direct current (HVDC) grids, as they allow to interconnect lines with different voltages and topologies. The dc-dc converters can increase the grid controllability adding power flow control, voltage regulation and/or fault blocking capability. The dc modular multilevel converter (dc-MMC) is a non-isolated solution proposed to interconnect HVDC systems with the same line topology. This paper proposes a new dc-MMC with a control strategy, which allows the converter to interconnect different line topologies (e.g., rigid bipole connected to a symmetric monopole). The paper presents the different line topologies in HVDC installations. Then, a mathematical model with a variable transformation is proposed for the new dc-dc converter. A control structure is proposed and implemented in Matlab/Simulink using an average arm model and simplified dc grids. The results validate the control in normal operation, fault blocking capability and post-fault scenario (degraded mode).

Active flow control in an S-shaped duct at Mach 0.4 using sweeping jet actuators

An experimental study was conducted on the flow control capability of sweeping jet actuators (SJAs) in an aggressive offset S-shaped duct with an inlet Mach number of 0.4. The SJAs were placed in two different spacing arrangements to suppress flow separation in the duct and flow distortion at the aerodynamic interface plane (AIP). Multiple measurements were taken, including surface oil flow visualization, steady pressure on the wall surface, five-hole probe pressure, and velocity at the AIP. For the baseline case without control, the surface oil flow visualization and pressure measurement results clearly reflected the three-dimensional flow separation characteristics in the duct. In the controlled cases, the streamwise surface pressure coefficient distribution showed that SJAs can effectively suppress the flow separation. At a spacing ratio of 8.13 and an excitation pressure of 250 kPa, the inflection point of the pressure coefficient Cp was completely eliminated. As a result, the absolute pressure recovery at the upper region of the AIP increased by nearly 5%, and the mean value and RMSE of the cross-flow velocity declined by 54.9% and 48.1%, respectively.

In-Flight Demonstration of Stall Improvement Using a Plasma Actuator for a Small Unmanned Aerial Vehicle

The flow control capability (especially for separation control) of a dielectric-barrier-discharge plasma actuator (DBD-PA) has been investigated extensively. However, these studies have been conducted under ideal conditions, such as wind tunnels and computational environments, and limited studies have investigated the effects of plasma actuators in an actual environment. In this study, the flow control capability of a DBD-PA under natural and in-flight conditions was investigated via field flight tests using an unmanned aerial vehicle (UAV). The DBD-PA driving system was constructed with a small high-voltage power supply on a 2-m-span UAV. With the support of an autonomous flight system, the pitch angle gradually increased as the airspeed decreased, and the stall occurred from the cruise state. This flight procedure was conducted with the DBD-PA on or off, and 246 pairs of flights were operated. The results revealed that a flight state with a higher pitch angle and lower airspeed occurred when DBD-PA was switched on. In addition, the moment of stall was quantitatively determined from the flight log, and it was confirmed that the maximum pitch angle when DBD-PA was switched on tended to be larger than that when DBD-PA was switched off. These results indicate that flow control with a DBD-PA on a 2-m-span UAV was effective in natural and in-flight situations.

A current‐limiting DC circuit breaker with power flow control capability

Power flow controller (PFC), fault current limiter (FCL) and DC circuit breaker (DCCB) are important equipment in the DC grid. There are a large number of power electronic components in these equipment, resulting in high cost. In order to reduce the use of additional components, a current-limiting DC circuit breaker with power flow control capability is proposed here, which integrates the PFC, FCL, and DCCB into one equipment. Further, the main breaker in the proposed circuit breaker is shared by all lines connected to a DC bus to reduce cost. The topology and operating principle of the circuit breaker are introduced. Theoretical analysis and parameter design are carried out. Besides, the proposed circuit breaker is verified in PSCAD/EMTDC. Finally, the performance and cost are compared with existing schemes. The simulation results show that the proposed circuit breaker can effectively realize power flow control, current limiting and fault isolation at a lower cost.

A multiport embedded DC power flow controller for ISOP-DCT

The DC transformers (DCTs) can achieve flexible power flow control in the ring-type and meshed-type multi-terminal DC grids with less loss. However, due to the limited power flow control range of the DCTs, the power flow controller (PFC) is expected to boost the system's controllability. Unlike the conventional DCTs, this paper proposes an embedded DC power flow controller (e-DCPFC) formed by a PFC and an input-series-output-parallel (ISOP) DCT. This device has the features of multiple ports and extended bidirectional power flow control capability. The operational principle of the e-DCPFC is analysed in detail. And a modified input voltage sharing (m-IVS) control strategy is proposed in this paper. This control scheme not only maintains the input capacitor voltage balanced of the ISOP structure but also controls the power of the extra ports provided by the e-DCPFC. The feasibility and effectiveness of the proposed topology and control strategy are verified via MATLAB simulation mode.

Power flow control capability analysis of unified power flow controller

In the field of power system restructuring, Flexible Alternating Current Transmission System (FACTS) technology has become indispensable for alleviating the challenges of load flow control, voltage control, transient stability, and dynamic stability. The Unified Power Flow Controller (UPFC) is the fastest, most flexible, and most capable FACTS device because it has the full advantage of providing simultaneous and independent real-time control of voltage, impedance, and phase angle, which are the main power system parameters that affect system performance. This paper uses a Newton-Raphson load flow that includes UPFC to analyze how UPFC can control the flow of power.

Operation and Control of an HVDC Circuit Breaker With Current Flow Control Capability

Deployment of dc circuit breakers (DCCBs) will help to isolate dc faults in dc systems. Conversely, current flow controllers (CFCs) will be employed in dc grids to balance currents among transmission lines. However, the inclusion of these devices may incur significant capital investment. A way to reduce costs is by integrating current control capabilities into DCCBs. This article presents a new device, the CB/CFC, which combines a multiline DCCB with a half-bridge based CFC. The operating principles of the device are analyzed and its operating modes are classified. A level-shift modulation method ensuring that a single bridge of the CB/CFC is modulated for each operating mode is considered. This simplifies the control scheme for CFC operation. For completeness, the CB/CFC is compared with other alternatives available in the literature. It is shown that the presented device reduces the number of semiconductor components compared to other solutions. DC fault isolation and current flow control are verified through simulations conducted in Power Systems Computer Aided Design (PSCAD).