Blown Flap Research Articles

Optimization of the double-slot blown airfoil with jet at the leading and trailing edges of the flap

An active lift augmentation technique combining trailing edge blowing and blown flap is explored in this study. A double-slot blown flap airfoil is designed based on NACA23015. By optimizing the configuration parameters via the neural network surrogate model and particle swarm optimization algorithm, the lift coefficient at the 8° angle of attack reaches ∼5.14, which is approximately a 24% increasement relative to the baseline single-slot blown flap airfoil. In the configuration optimization, a longer flap facilitates lower pressure on the upper airfoil surface. Additionally, the aerodynamic flap effect caused by the double-slot jet flow intensifies the lift peaks and the pressure decreases over the airfoil. Ultimately, redistributing the jet momentum to the two slots achieves a highly efficient blown flap airfoil design.

The Honda Automotive Laboratories of Ohio Wind Tunnel

<div class="section abstract"><div class="htmlview paragraph">The Honda Automotive Laboratories of Ohio (HALO) includes a new aeroacoustic wind tunnel located near Marysville, Ohio that started operations in 2022. This facility provides world-class aerodynamic flow quality and acoustic testing capabilities for the development of both passenger and motorsports vehicles.</div><div class="htmlview paragraph">This closed-return ¾ open jet wind tunnel features a two-position flexible nozzle system with cross sections of 25 m<sup>2</sup> and 18 m<sup>2</sup>, providing wind speeds of up to 250 km/h and 310 km/h, respectively. There is a ±180 degree turntable with boundary layer control systems, and interchangeable single belt and 5-belt moving ground plane (MGP) modules. Extensive applications of acoustic treatment in the test section and throughout the wind tunnel circuit provide a hemi-anechoic test environment and low background noise levels. A temperature control system provides uniform and stable air temperature over an operating environment between 10 °C and 50 °C.</div><div class="htmlview paragraph">The primary instrumentation of the wind tunnel includes the wind speed, temperature, and humidity measurement systems, a 6-component force balance integrated within the turntable, and an acoustic test system (ATS). The ATS includes four planar microphone arrays for external measurements and a spherical microphone array and binaural heads for internal measurements. A flow survey traverse system equipped with a 4-D probe holder mechanism is capable of placing a probe anywhere within the test volume.</div><div class="htmlview paragraph">The HALO facility includes the wind tunnel control room, secure vehicle preparation bays and office spaces for segregated customers, and a vehicle frontal and side area measurement system.</div><div class="htmlview paragraph">This paper provides an introduction to the HALO wind tunnel testing capabilities, design features and development, and the results of the aeroacoustic commissioning program. The background noise level and flow quality characteristics are provided.</div></div>

Design and optimization of a transmission mechanism developed for distributed electric propulsion aircraft

In order to obtain better aerodynamic efficiency and take-off/landing capacity, it will be an excellent configuration for distributed electric propulsion (DEP) aircraft to install the blown flap in the propulsion wake. For this configuration, the coupling motion between the blown flap and the duct is hard to be achieved by the transmission mechanism of traditional distributed electric propulsion aircraft. This article describes the design and optimization of a transmission mechanism of a high lift device which composed of the distributed electric propulsion system and the blown flap. Firstly, the theoretical design rationale which is mainly based on the analytic hierarchy process and ant colony algorithm is introduced. Then, the kinematic simulation is conducted in details using closed loop vector equation. To further demonstrate the feasibility and reliability of the design approach, the functional test of a full-size transmission mechanism model is carried out. Kinematic simulation and ground test results show that the proposed mechanism can meet the requirements of the coupling motion between the duct and the blown flap, and the corresponding design scheme can be used to solve the design problem of such DEP aircraft transmission mechanism with the blown flap.

CFD Wind Tunnel Assessment on the case study of the MOTHIF Blown Flap

The increasing interest in Small Air Transportation (SAT), to enhance global connectivity, is highlighting the need for reducing take-off distance: lift coefficient has to be increased without penalizing the configuration drag, weight and complexity.Within the EU Clean Sky 2 projects, a blown flap configuration has been developed to allow STOL capabilities of a future affordable and green commuter belonging to EASA CS 23.The blowing system design choice is aimed at keeping the inevitable associated increase in pitching moment very low, and not penalizing performance when blowing fails.In collaboration between Piaggio Aerospace and the MOTHIF consortium, a wing model was designed, built and tested in the VKI’s large subsonic L1-A wind tunnel, reproducing bi-dimensional preliminary results obtained during the design phase.In order to reduce and predict three dimensional and blockage effects, CFD has been used extensively to obtain a proper test chamber configuration and to reproduce some wind tunnel test results, so that both the accuracy of wind tunnel and design methodology can be assessed.This work presents the comparison between experimental data and CFD simulations to demonstrate the usefulness of simulations to reduce both the risk for erroneous results in experimental activities and their related cost.

Extended Study of Full-Scale Wind Tunnel Test and Simulation Analysis Based on DrivAer Model

There is a great demand for car model series that can meet the needs of today’s research about vehicle aerodynamics due to the limitations of models used in the past. This paper focuses on the introduction of the extension of DrivAer model and discussions about the model’s experimental and simulation results. On the basis of DrivAer model, the upgrade and innovation of pickup styling back and concept of perception testing are added. Specifically, the SUV back and the Pickup back are redesigned in combination with Chinese aerodynamic design trend. The experiments were performed in a full-scale aero-acoustic wind tunnel with ground simulation system, consisting of boundary layer control system and five-belt system. Base on the wind tunnel experimental results, it can be found that the ground simulation has obviously influence on the drag coefficient, but has no influence on the distribution of surface pressure in upper body. The close state of the grilles, the absence of mirrors, and the fully enclosed of rims can significantly reduce the drag coefficient. Digital wind tunnel (DWT) simulation and open road (OR) simulation have been completed and verified with experimental results. It can be concluded that DWT simulation with the same geometry as the real wind tunnel performs better than the OR simulation. The maximum difference between the experimental results and the DWT simulation results does not exceed 2% and DWT simulation also performs well in the surface pressure simulation.

Characteristics improvement of spatial fixed-geometry air intakes of external compression based on boundary layer control systems application

Characteristics improvement of spatial fixed-geometry air intakes of external compression based on boundary layer control systems application

Design and Experimental Characterization of an Actuation System for Flow Control of an Internally Blown Coanda Flap

The focus of the work is on the evaluation, development and integration of a robust actuator system for three-dimensional flow control of a blown Coanda flap to improve the high lift system of commercial aircraft. As part of the research work presented, the system is integrated into a wind tunnel model in order to influence the flow across the entire width of the model. The system developed is based on individual bending transducers that can vary the height of the blowing slot dynamically. The system is divided into 33 segments and is therefore able to implement static and dynamic actuation along the wing-span (3D-actuation). All segments can be controlled independently and thus offer great optimization potential for an effective flow control. Different configurations were developed and evaluated against each other with respect to the demanding requirements (small installation space, frequency range from 5 Hz to 300 Hz, 1 bar pressure, 0.4 mm deflection, 1 m span). The design of the blown flap has been specified in an iterative design process. In the final configuration, all mechanical components are reduced to the bare minimum for weight reduction reasons, in order to meet the dynamic requirements of the wind tunnel model. To characterize the lip segments, a test device has been designed that can be pressurized to generate aerodynamic loads on the lip segments. Finally, 33 lip segments were integrated into a wind tunnel model and tested intensively as part of a measurement campaign. The first aerodynamic results show an increase in lift of up to ∆Ca = 0.57. These aerodynamic gains are achieved at amplitudes that do not require the lip segments to completely close or open the blowing slot, which shows the advantage of the current lip design that enables activation with independently controlled stationary and unsteady components.

Effects of Geometrical Parameters of Internal Blown Flap and Its Optimal Design

The internal blown flap was numerically simulated. Firstly, a parameterization method was developed, which can properly describe the shape of the internal blown flap according to such geometrical parameters as flap chord length, flap deflection, height of blowing slot and its position. Then the reliability of the numerical simulation was validated through comparing the pressure distribution of the CC020-010EJ fundamental generic circulation control airfoil with the computational results and available experiment results. The effects of the geometrical parameters on the aerodynamic performance of the internal blown flap was investigated. The investigation results show that the lift coefficient increases with the increase of flap chord length and flap deflection angle and with the decrease of height of blowing slot and its front position. Lastly, a method of optimal design of the geometrical parameters of the internal blown flap was developed. The design variables include flap chord length, flap deflection, height of blowing slot and its position. The optimal design is based on maximum lift coefficient, the angle of attack of 5 degrees and the design constraint of stall angle of attack of less than 9 degrees. The optimization results show that the optimal design method can apparently raise the lift coefficient of an internal blown flap up to 1.7.

Optimization and Analysis of a Blown Flap Based on a Multielement Airfoil

The present study proposes a new configuration of an internally blown flap based on a multielement airfoil for the high-lift system of an amphibious aircraft. Triobjective optimization based on computational fluid dynamics is carried out. The optimization results show that the present configurations have efficient lift enhancement and reach the tradeoff of the lift to drag ratio and low angle-of-attack performance. The optimized configuration also has good stall behavior and better poststall performance. A parametric analysis is conducted to test the sensitivity of each design parameter, and the results prove the robustness of the configuration. The results of different jet momentum coefficients show that two critical values exist that separate the lift versus jet momentum curve into three segments corresponding to different flow phenomena, which indicates that the circulation control rule for a multielement airfoil with a blown flap is different and more complicated.

Improving the Lift Properties of a Wing in Takeoff and Landing by Means of a Boundary Layer Control System Using Ejector-Type Actuators

A device making it possible to control of the flow past a wing at low flight speeds is proposed. The device comprises an ejector-type actuator that simultaneous sucks the boundary layer on the upper surface and blows a gas jet in the vicinity of the trailing edge. Based on the Reynolds-averaged Navier–Stokes equations, a mathematical model of an ejector-type actuator is developed and experimental studies are carried out.

Influence of engine modeling on structural sizing and approach aerodynamics of a circulation controlled wing

Extended configurations of a short take-off and landing aircraft under investigation at the Coordinated Research Centre SFB 880 include a morphing droop nose and a tractor propeller engine. The short take-off and landing capabilities are achieved by circulation control via a high velocity jet over the flap leading edges utilizing the Coandǎ effect. The effect of the engine integration in combination with the blown flaps on the wing sizing, aerodynamic performance, and static wing deformation are of large interest. High-detail structural wing models are sized with a fully stressed approach using a partitioned fluid–structure interaction process. The aerodynamic part is covered by highly detailed computational fluid simulations. The effect of modeling the engine on the global and local aerodynamics for different levels of circulation control has a large impact. In addition, a change in flow separation behavior due to the engine effects is observed. The wing mass is only slightly increased by the detailed engine aerodynamics and the separation behavior changes slightly for the elastic wing. These findings show that the modeling of the engine will lead to a different stall behavior and allow for a higher lift, while the influence on the wing structure and aeroelasticity are very small.

Flight mechanics model for spanwise lift and rolling moment distributions of a segmented active high-lift wing

In this study, the aerodynamics of wings using an active high-lift system are investigated. The target is the flight mechanical description of the spanwise forces and resulting moments and the influence of the active high-lift system to their distribution. The high-lift system is a blown flap system divided into six segments per wing. Each segment is assumed to be individually controlled, so the system shall be used for aircraft control and system failure management. This work presents a flight mechanical sub-model for the simulation of flight dynamics, which has been derived from high-fidelity CFD results. An assessment of single-segment blowing system failures will be presented including recommendations for compensation of either lift or rolling moment loss. For this investigation, the compensation is required to act at the same wing side on which the failure appears. Thus, the potential for an increase of system reliability shall be proven. The results show that less performance investment in terms of pressurized air is necessary to compensate the rolling moment of a failing segment instead of its lift. However, large blowing performance increases for the remaining wing segments that occur for some of the failure cases.

A parametric study on the influence of boundary conditions on the longitudinal pressure gradient in CFD simulations of an automotive wind tunnel

Computational fluid dynamics (CFD) is an important and extensively used tool for aerodynamic development in the vehicle industry today. Validation of virtual methods by comparison to wind tunnel experiments is a must because manufacturers aim to substitute physical tests on prototype vehicles with virtual simulations. An appropriate validation can be performed only if the wind tunnel geometry with representative boundary conditions is included in the numerical simulation, and if the flow of the empty wind tunnel is accurately predicted. One of the important flow parameters to predict is the longitudinal pressure distribution in the test section, which is dependent on both the wind tunnel geometry and the settings of the boundary layer control systems. This study investigates the effects of flow angularity at the inlet and different boundary layer control systems, namely, basic scoop suction, distributed suction, and moving belts, on the longitudinal pressure distribution in the full-scale aerodynamic wind tunnel of Volvo Cars using CFD and a systematic design of experiments approach. The study shows that the different suction systems used to reduce boundary layer thickness upstream of the vehicle have statistically significant effects on the longitudinal pressure distribution in the test section. However, the estimated drag difference induced on a typical vehicle by the difference in horizontal buoyancy between the tested settings is within the test-to-test uncertainty of the physical wind tunnel, thereby leading to the conclusion that force calculations in simulations are fairly insensitive to the tested parameters on the investigated intervals.

Numerical Investigation of Powered High-Lift Model with Externally Blown Flap

The externally blown flap is an approach of powered-lift technology utilizing conventional pod-mounted engines to blow exhaust over the flap surfaces. Based upon multiblock structured grid techniques and three-dimensional Reynolds-averaged Navier–Stokes computational methods, a powered high-lift principle model with externally blown flap is constructed for analysis. Different influencing factors, including engine position, engine-exhaust condition, flap deflection, and flap gap, are investigated in detail to improve powered high-lift effects. Then, flow-control techniques, such as the cove tab and downward deflection of the spoiler, are studied. The cove tab can be helpful for longitude-trim and stability problems, whereas the spoiler downward deflection can help increase lift-to-drag ratios. Both the cove tab and spoiler downward deflection can contribute to the augmentation of the lift coefficients and the elimination of the flow separation over the flap, as well as the reduction of jet-flow spanwise spreading on the leading edge of the lower flap.

Investigation of Aeroelastic Effects of a Circulation Controlled Wing

The aeroelastic behavior of the wing of a 100-passenger aircraft under investigation in the Coordinated Research Center SFB 880 is studied. A compressed air jet upstream of the high-lift devices called the Coandă jet enables boundary layer control with delayed flow separation and consequently high lift. Aeroelastic instabilities caused by boundary layer control systems are critical to the aircraft performance. The understanding of cause and effect of these instabilities is of great importance. For analyses, a multilevel approach is pursued using full-scale three-dimensional models and reduced-order models. Both model types use fluid-structure interaction techniques. The full-scale models are used to generate a sized wing structure with realistic mass and stiffness distributions using computational fluid dynamics loads of cruise and landing configuration load cases. A reduced-order model is derived by modal reduction for computationally efficient investigations of multiple flight states. To study local aeroelastic effects and to develop three-dimensional corrections for the reduced-order model, full-scale three-dimensional coupled fluid-structure analyses are investigated. The results show that especially the dynamic behavior of wings with active circulation control may differ significantly from that of conventional wings due to the different aerodynamic behavior caused by the Coandă jet.

Numerical Simulation of Powered High-Lift Flow

To achieve short-take-off-and-landing (STOL) performance, numerous airframe/propulsion integration (API) technologies have been developed for military and commercial transports. Powered lift technology refers to a concept of utilizing the propulsion exhaust flows to increase lift through an increase in wing circulation []. Over the past seventy years, various concepts have been explored to accomplish this goal. From the point of view of technical characteristics, powered lift concepts can be sorted into three groups: a circulation control wing, blown flaps, and jet wing. Most of other concepts are slight deviations of these three.

Design of a high-lift experiment in water including active flow control

This paper describes the structural design of an active flow-control experiment. The aim of the experiment is to investigate the increase in efficiency of an internally blown Coanda flap using unsteady blowing. The system uses tailor-made microelectromechanical (MEMS) pressure sensors to determine the state of the oncoming flow and an actuated lip to regulate the mass flow and velocity of a stream near a wall over the internally blown flap. Sensors and actuators are integrated into a highly loaded system that is extremely compact. The sensors are connected to a bus system that feeds the data into a real-time control system. The piezoelectric actuators using the d33 effect at a comparable low voltage of 120 V are integrated into a lip that controls the blowout slot height. The system is designed for closed-loop control that efficiently avoids flow separation on the Coanda flap. The setup is designed for water-tunnel experiments in order to reduce the free-stream velocity and the system’s control frequency by a factor of 10 compared with that in air. This paper outlines the function and verification of the system’s main components and their development.

Aerodynamic Installation Effects of an Over-the-Wing Propeller on a High-Lift Configuration

Preliminary design studies indicate that a cruise-efficient short takeoff and landing aircraft has enhanced takeoff performance at competitive direct operating costs when using high-speed propellers in combination with internally blown flaps. The original tractor configuration is compared to an over-the-wing propeller, which allows for noise shielding. An additional geometry with partially embedded rotor similar to a channel wing is considered to increase the beneficial interaction. This paper shows the aerodynamic integration effects with a focus on climb performance and provides an assessment of the three aforementioned configurations for a simplified wing segment at takeoff conditions. Steady Reynolds-averaged Navier–Stokes simulations have been conducted using an actuator disk model and were evaluated based on the overall design. Interacting with the blown flap, the conventional tractor propeller induces large lift and drag increments due to the vectored sliptream. Although this effect is much smaller for an over-the-wing configuration, by halving the lift augmentation, the lift-to-drag ratio and the propulsive efficiency are considerably improved. Besides a moderate lift gain, the main advantage of a channel wing design is the location of the thrust vector close to the center of gravity resulting in a smaller nosedown pitching moment due to thrust. A disadvantage of over-the-wing propellers is the inhomogeneous inflow at higher velocity, which leads to oscillating blade loads and reduced efficiency.

Multidisciplinary conceptual design for aircraft with circulation control high-lift systems

Active high-lift technologies have often proven their potential in aerodynamic analyses and wind tunnel tests, but have so far played only a minute role in civil production aircraft. This is expected to change in the future only if such technologies can be accounted for early in the aircraft design process. In this paper, the adaptation of a conceptual design process is presented, enabling it to consider circulation control as a high-lift technology. It is shown that the main aerodynamic effects of a blown flap in the boundary layer control regime can be satisfactorily modeled with a potential theory method. Some sample results of the design process indicate a potential for significant reductions of required field length in comparison with today’s aircraft, creating the potential to increase the capacity of the air transportation system, without increasing overall aircraft mass or direct operating cost.

Active Boundary Layer Control System Using Vortex Generating Jets and Operating by the Detection of Precursor of Flow Separation

Longitudinal vortices produced by the interaction between jets and a freestream are useful in enhancing boundary layer mixing and have proven to be effective for controlling flow separation. This technique, known as the vortex generating jet (VGJ) method, serving as an active control provides a time-varying control action to optimize performance under a wide range of flow conditions, because the strength of the longitudinal vortices can be adjusted by varying the speed of the jet. In the present study, an active separation control system using VGJs is proposed and is applied to the practical problem of flow separation control in a two-dimensional diffuser. The proposed system can be operated prior to the onset of separation, and therefore, a separation control is always attained with no flow separation for all the flow fields examined. The experimental results indicate that the growth of shear layer vortices at the corner of the diffuser inlet is a precursor to the large-scale separation over entire surfa...