Laminar Flow Control System Research Articles

Three-Dimensional Fluctuating Flow of a Second-Grade Fluid along an Infinite Horizontal Plate with Periodic Suction

Laminar flow control plays a vital role in reducing drag resulting enhancement in the vehicle power by a significant amount. Theoretical and experimental studies have proven that the transition from laminar to turbulent flow (causing the drag coefficient to enhance) may be delayed/prevented by the suction of the fluid from the boundary layer to the wall. The purpose of this work is to study the effects of periodic suction on the unsteady 3-dimensional fluctuating flow of a second grade incompressible fluid flowing laminarly over a horizontal porous infinite plate. The plate is subjected to a sinusoidal transverse suction velocity while the free stream velocity oscillates in time about a constant mean. The flow turns out to be 3-dimensional because of transverse direction of the periodic suction velocity. By the series expansion method, analytic expressions for transient velocity, skin friction components, and pressure are attained. Impact of nondimensional parameters evolving in the mathematical model of the problem on these physical quantities are visualized graphically and discussed analytically. The velocity component u is found to be rising with a growth in suction parameter α. The pressure is noted to be growing with a growth in Reynolds number R e . Further, due to suction at the plate and transient free stream velocity, the pressure increases near the plate and then reaches to a steady value far-off the plate. The skin friction along the main flow is noticed to be decreasing with the rise in α for 0.5 ≤ R e ≤ 1.4 , however, an exponential rise is observed for R e > 1.4. The skin friction along the cross flow is noted to be enhancing for the rising values of suction parameter and elastic parameter. The present results have excellent agreement with previous published results in the limiting sense. This study is beneficial in designing and manufacturing laminar flow control system to enhance the vehicle power requirement.

Analysis and Uncertainty Quantification of a Hybrid Laminar Flow Control System

This study aims to quantify suction velocities for hybrid laminar flow control of a vertical fin by taking data and model uncertainties into account. Because suction velocities cannot be measured directly, they are calculated using the Darcy–Forchheimer model, which needs the pressure distribution and porosity characteristics as input. Uncertainties in the pressure distribution are characterized using a novel data fusion method incorporating wind-tunnel and numerical data. Furthermore, geometrical uncertainties of the airfoil that alter the pressure distribution are considered. Two methods are proposed to model the porosity characteristics of the surface: one of which uses a local representation, and the other a global representation. In addition, the modeling error of the Darcy–Forchheimer model is estimated. These input uncertainties are quantified and propagated by Monte Carlo sampling through the Darcy–Forchheimer model. It reveals that local information on the porosity characteristics is essential for accurate suction velocity estimates for this specific application. A sensitivity study shows that the most influential contribution to the variance of suction velocities is the uncertainty in the porosity characteristics, followed by uncertainties in the pressure distribution. The model error and uncertainties in the reference pressure are shown to have a negligible influence.

Mode I fracture toughness of asymmetric metal-composite adhesive joints

In this work, the mode I fracture toughness of dissimilar metal-composite adhesive joints is experimentally investigated using the double cantilever beam (DCB) test. The particular joint under study is resulted by the adhesive joining of a thin titanium sheet with a thin carbon fiber reinforced plastic (CFRP) laminate and is envisioned to be implemented in the hybrid laminar flow control system of future aircraft. Four different industrial technologies for the joining of the titanium and CFRP adherents are evaluated/compared; co-bonding with and without adhesive and secondary bonding using either thermoset or thermoplastic CFRP. The vacuum-assisted resin transfer molding (VARTM) technique is employed for the manufacturing of the panels. After manufacturing, the panels are cut into test specimens that, because they are too thin (approximately 2.4 mm thick), needed to be stiffened from both titanium and composite sides with two aluminum backing beams to ensure the non-yielding of the titanium during the subsequent DCB tests. Towards the determination of the fracture toughness of the joint from the experimental data, an analytical model recently developed by the authors, that considers the bending-extension coupling of both sub-laminates constituting the test specimen as well as the manufacturing-induced residual thermal stresses, is applied. For the four manufacturing options (MO) investigated, the load-displacement behaviors, failure patterns, and fracture toughness performances are presented and compared.

Preliminary Design and System Considerations for an Active Hybrid Laminar Flow Control System

Hybrid laminar flow control or HLFC design is a complex and multi-disciplinary process, which demands a thorough understanding of all aspects from a global systems viewpoint. The objective of the paper is to present a preliminary design of important components of an HLFC system that helps in quick assessment of conceptual system architectures. This is important to evaluate feasibility, system performance, and overall aircraft benefits at early stages of system development. This paper also discusses the various important system requirements and issues concerning the design of active HLFC systems, and the interfaces between various disciplines are presented. It can be emphasized from the study that the future compressor design for the HLFC system should consider the thermal management aspects and additional mass flow requirements from the aerodynamics-structure design optimization and also from water drain system solutions. A method to calculate the accumulated water content inside the plenum chambers is presented, and the effect of a drain hole on the power consumption is studied. A low order thermal management study of the HLFC compressor motor shows a high temperature rise in the windings for very high speed motors for long duration operation and calls for effective cooling solutions.

An experimental study on the effects of two-dimensional positive surface defects on the laminar–turbulent transition of a sucked boundary layer

Laminar–turbulent transition can be effectively delayed using Laminar Flow Control (LFC) by boundary layer suction. However, major obstacles to the industrial implementation of this technique are related to practical limitations, such as proper integration of the suction system or unreliability of current design tools. The influence of surface discontinuities that can arise from installing an LFC system (and then potentially cancel or deteriorate its stabilizing effect on the boundary layer) is scarcely documented in the open literature, adding to the complexity of improving numerical models. The present investigation, therefore, focuses on experimentally characterizing the effects of surface defects on the laminar–turbulent transition of a sucked boundary layer in a two-dimensional flow, in an effort to address some of the issues mentioned above. The experimental facility and protocol for conducting this transition study are first presented, followed by a baseline characterization of the effects of wall suction alone on transition. Surface defects, in the form of cylindrical roughness elements (wires), are then introduced on the flat plate and their effects, coupled to those of wall suction, on boundary layer stability are discussed. The critical relative height (where the onset of transition coincides with the position of the surface defect) was found to be the same for cases both with and without wall suction. For the critical cases, spectral analysis of the flow immediately downstream of the defect for all suction configurations revealed a range of amplified high frequencies in addition to or in place of the natural Tollmien–Schlichting instabilities. Wall suction was, therefore, ineffective in delaying the critical relative wire height, since, in the critical cases, the transition mechanism seemed to be governed by inflection-type instabilities, rather than viscous instabilities.

Mode II fracture toughness of asymmetric metal-composite adhesive joints

The paper presents an experimental investigation of the mode II fracture toughness behavior of dissimilar metal-composite adhesive joints using the end-notched flexure (ENF) test. The adhesive joint under study consists of a thin titanium sheet joined with a thin CFRP laminate and is envisioned tobe applied in the hybrid laminar flow control system of future aircraft. Four different industrial technologies for the manufacturing of the joint areevaluated; co-bonding with and without adhesive and secondary bonding using either a thermoset or a thermoplastic composite. The vacuum-assisted resin transfer molding (VARTM) technique is employed for the manufacturing of the titanium-CFRP joint. After manufacturing, the joint is stiffened from its both sides with two aluminum backing beams to prevent large deformations during the subsequent ENF tests. Towards the fracture toughness determination from the experimental data, an analytical model recently reported by the authors is applied; that model considers the bending-extension coupling of each sub-laminate of the joint as well as the effect of the manufacturing-induced residual thermal stresses. The load-displacement behaviors, failure patterns, and fracture toughness performances for each of the four manufacturing options (MO) investigated are presented and compared.

層流制御システムをとりいれた航空機の概念設計手法に基づく性能検討

層流制御システムをとりいれた航空機の概念設計手法に基づく性能検討

Computational Simulated Verification of Hybrid Laminar Flow Design by Suction Method

Rise in the performance and therefore profit of airliners is a major challenge for aircraft designers. Here, the design of a Hybrid Laminar Flow Control system is considered and a computational verification has been done to show the performance of the system and by employing the fundamental equations, it showed that the required level of suction across a wing to efficiently suppress flow is achievable. A novel system was designed that could be incorporated into the leading edge of large civil aircraft or adapted to suit alternative aircraft using a combination of active and passive suction methods. A turbo compressor has been employed to provide the certain level of suction, whereas the passive system automatically produces suction by introducing ducting from the high pressure region at the leading edge to the low pressure region at the underside of the wing. By this method the fuel saving of 5% is achievable. The outcome of the investigation shows a good meeting with computational analysis and the available source of validation. This method is recommended to be experimentally investigated.

Influence of Offdesign Performance on Design Synthesis of Laminar Aircraft

Laminar flow is among themost discussed technologies toward satisfying the ambitious goals ofmore fuel-efficient aviation. Both passive as well as active laminar flow control systems are sensitive to external influences and system failures. A sudden degradation of laminarflow immediately results in loss offlight performance. Such offdesign cases have to be considered in preliminary design synthesis for correct sizing of the aircraft. In the scope of this paper, an approach is presented that incorporates offdesign cases of laminar aircraft into preliminary design synthesis. The authors chose to use the extended-range twin-engine performance standards as a framework for deriving operational standards for aircraft with laminar technology. Different requirements for minimum offdesign performance are derived that directly impact overall aircraft design synthesis. In a case study, the sensitivities of the design synthesis toward these offdesign requirements are discussed. Design parameters such as maximum takeoff weight, block fuel, as well as the aircraft economics are used for evaluation of the different concepts.

The response of a flat plate boundary layer to an orthogonally arranged dielectric barrier discharge actuator

The jetting characteristics of dielectric barrier discharge (DBD) actuators make these devices suitable for augmenting boundary layer flows. The associated change to the hydrodynamic stability of the fluid arising from the actuator provides a mechanism through which a DBD-based laminar flow control (LFC) system can be developed. Historically, DBD actuators with electrodes arranged parallel to each other have been used for LFC with mixed results. An alternative is to use an actuator with electrodes placed orthogonally to each other. Orthogonally arranged actuators exhibit different jetting characteristics to conventional ones, and as such understanding the effect that these actuators have on the mean velocity profile within a flat plate boundary layer is of significant interest to the development of DBD-based LFC technology. In this investigation, the velocity distribution within a flat plate boundary layer in a zero pressure gradient is measured in response to the operation of an orthogonally arranged actuator. The results suggest that significant thinning of the boundary layer can be realized with an orthogonally arranged actuator, over a short distance downstream of the device, and used in conjunction with a subtle suction effect, this thinning can be exacerbated. However, further downstream, rapid thickening of the layer, supported by a decrease in the shape factor of the flow suggests that the layer becomes unstable, in an accelerated fashion, to the presence of the actuator. Hence the stability of the layer is found to be significantly altered by the presence of the orthogonally arranged actuator, a requisite for a LFC system. However, since the actuator produces a destabilizing effect, the development of a successful LFC system based on orthogonal actuators will require further work.

PARABOLIZED STABILITY EQUATIONS

▪ Abstract Parabolized stability equations (PSE) have opened new avenues to the analysis of the streamwise growth of linear and nonlinear disturbances in slowly varying shear flows such as boundary layers, jets, and far wakes. Growth mechanisms include both algebraic transient growth and exponential growth through primary and higher instabilities. In contrast to the eigensolutions of traditional linear stability equations, PSE solutions incorporate inhomogeneous initial and boundary conditions as do numerical solutions of the Navier-Stokes equations, but they can be obtained at modest computational expense. PSE codes have developed into a convenient tool to analyze basic mechanisms in boundary-layer flows. The most important area of application, however, is the use of the PSE approach for transition analysis in aerodynamic design. Together with the adjoint linear problem, PSE methods promise improved design capabilities for laminar flow control systems.

A Parallel Processing Approach to Transition Prediction for Laminar Flow Control System Design

The performance of transport aircraft can be considerably improved if the process by which the wing boundary layer becomes turbulent can be controlled and extensive areas of laminar flow maintained. In order to design laminar flow control systems, it is necessary to be able to predict the movement of the transition location in response to changes in control variables, e.g., surface suction. At present, the technique which is available to industry requires excessively long computational time – so long that it is not suitable for use in the "design process." Therefore, there is a clear need to produce a system which delivers results in near realtime, i.e., in seconds rather than hours. This article details how parallel computing techniques on a KSR‐1 produce these performance improvements.