Aeronautical Research Research Articles

Calibrated consistent flow generator for tall building aerodynamics using large eddy simulation

Ensuring proper matching of the target wind characteristics of the inflow is vital for the accuracy of both experimental and numerical wind studies. In the current study, a calibrated turbulent inflow generation technique was developed to accurately simulate the inflow boundary condition for large eddy simulation (LES) of the lower region of the atmospheric boundary layer (ABL) based on a newly developed technique, namely consistent discrete random flow generator (CDRFG). The proposed technique, namely Calibrated-CDRFG (C-CDRFG), targets specific incoming turbulence at distances downstream to account for dissipation of the turbulent kinetic energy. The proposed technique generates accurate turbulent velocities with proper turbulence intensity, spectra, coherency, and correlation at the target distance downstream for a range of terrain conditions. The technique was validated by evaluating the wind-induced loads and responses for the Commonwealth Advisory Aeronautical Research Council (CAARC) and comparing that to the existing wind tunnel (WT) wind-induced response for the angle of attack (AOA) ranging between 0° and 90°. It was found that the resulting wind-induced response from the C-CDRFG technique resulted in an average matching of 91% of the wind tunnel results. The proposed technique is believed to be computationally efficient, flexible, and easy to be sustainable for parallel computing environments and thus provides significant value for Large Eddy Simulation (LES) wind engineering applications.

Characterizing wind pressure on CAARC standard tall building with various façade appurtenances: An experimental study

Tall buildings are usually considered as wind-sensitive structures. While extensive studies have been conducted concerning the wind load characteristics on tall buildings, the effect of façade appurtenances has not been fully understood. In this study, a 1:300 scaled CAARC (Commonwealth Advisory Aeronautical Research Council) standard tall building was tested in wind tunnel to diagnose the effect of various façade appurtenances on wind pressure characteristics. It is shown that, the change of façade appurtenances can significantly influence the fluctuating wind pressure on the windward and leeward surfaces, with the maximum reduction reaching 21%. By contrast, the effect of façade appurtenance on mean wind pressure is somewhat less pronounced. The results also indicated that adding vertical strips is likely to reduce the horizontal coherence of surface wind pressure, with the maximum reduction of horizontal coherence coefficient reaching 38%. Comparatively, the effect of façade appurtenance on vertical coherence is less significant.

Highlights of aeroacoustic tests of a metal spacecraft cabin ventilation fan prototype

A metal spacecraft cabin ventilation fan suitable for aerodynamic and acoustic ground tests was designed and tested in the NASA Glenn Research Center Acoustical Testing Laboratory. The fan design featured a low-noise blade-vane count that was chosen to reduce the rotor-stator interaction tone noise. The fan was throttled through its operating range, and results indicated that the measured aerodynamic and acoustic performance was in good agreement with predictions. Recommendations for further research of quiet high-performance fans intended to support long duration human space exploration missions are offered. This small fan aerodynamic and acoustic test rig and the NASA Glenn Acoustical Testing Laboratory are valuable resources available for supporting NASA's aeronautics research and space exploration missions.

Gender differences in peer review of innovation

AbstractResearch SummaryGender differences in peer review and the associated impact on innovation financing are well documented but less well understood. We study peer review in the National Aeronautics and Space Administration Small Business Innovation Research program, a public initiative seeking to increase women's access to innovation funds. We theorize that reviewers use status characteristics inappropriately as heuristics and create gender bias. Econometric analysis shows evidence of direct bias against female applicants, an effect linked to challenges for newcomers in demonstrating individual legitimacy rather than concerns about the organizational legitimacy of the associated firm. We also demonstrate a corrective redistribution to reverse this bias and create equity in the funding outcome. As these results negatively impact diversity in innovation, we propose policy recommendations to overcome this bias.Managerial SummaryPeer review is an important mechanism to rank and select technical proposals for funding. We examine the role of gender in a government program conducting this process. Controlling for the proposal quality and other factors, we show that the gender of the proposer is linked to lower scores. This effect is associated with proposals from females who are new to the program, suggesting their challenges in demonstrating credibility as leaders of these projects, and exacerbated by the fact that women represent a disproportionately high share of newcomers. Subsequently, the program reverses this bias such that the funding outcomes do not show the same inequities. This has important implications for policies supporting gender diversity in innovation.

Machine learning based algorithms for wind pressure prediction of high-rise buildings

In recent years, machine learning (ML) techniques have been used in various fields of engineering practice. In order to evaluate the feasibility of machine learning algorithms for prediction of wind-induced effects on high-rise buildings, four ML algorithms including ridge regression, decision tree, random forest and gradient boosting regression tree are adopted in this study to predict wind pressures on Commonwealth Advisory Aeronautical Research Council standard tall building. The gradient boosting regression tree model is proved to be well performed in predicting both mean wind pressures and fluctuating wind pressures. Compared to expensive wind tunnel tests and time-consuming computational fluid dynamic simulations, it is expected that the gradient boosting regression tree model is an efficient and economical alternative for predicting wind pressures on high-rise buildings.

XTAL VR System Use in a Novel AAM Research Cockpit

The Flight Simulation Facilities (FSF) at the National Aeronautics and Space Administration's (NASA) Langley Research Center (LaRC) provide high-fidelity, man-in-the-loop (MITL) and hardware-in-the-loop (HITL) simulation services to a number of research customers including NASA, academia, aviation industry partners, and other government agencies such as the Federal Aviation Administration (FAA) and the National Transportation Safety Board (NTSB). The Simulation Development and Analysis Branch (SDAB) management has determined that future research related to the emerging Advanced Air Mobility (AAM) sector will require a new type of simulator with a vastly different cockpit layout and field of view requirements for the out-the-window visual systems than any of the current cockpits. This new simulator might also benefit from integrated head-mounted displays (HMD). For these reasons, SDAB has decided to design and build a new cockpit that will meet the future AAM electric Vertical Take-Off and Landing (eVTOL) simulator needs. In this paper, the authors discuss the novel use of state-of-the-art head worn devices (HWD) to present augmented reality (AR) and virtual reality (VR) environments to researchers to improve the quality of the cockpit design and reduce the time-to-market and cost to obtain the new cockpit.

Optical fibre based sensors application to structural health monitoring in composite materials

Structural health monitoring (SHM) by means of embedded fibre optic (FO) sensors is able to perform diagnosis and prognosis of structural damages and defects. SHM system monitor structural status based on the acquired data resulting in the detection and characterization of damages and defects without necessity for the aircraft to be on ground. Optical fibre sensors are permanently installed in the structure and trigger maintenance actions only when a damage or defect of a particular size is detected. To demonstrate the potential of FO sensors technology and their application by means of embedded sensors to composite material aerostructures, manufacturing trials have been performed and the influence in mechanical behaviour of the sensors’ embedding has been studied by performing tests campaings, at coupon level, for experimental validation. This study is within the scope of SHERLOC, a project belonging to the Clean Sky 2 JU aeronautical research and development program, and of which main objective is to combine advanced Structural Health Monitoring (SHM) and smart repair technologies with a probabilistic design philosophy, and hence to develop new maintenance concepts to reduce the direct operative costs without lowering the operational safety of a composite fuselage.

Certification of Testing Laboratories – The Basis of Reliability Among Research Vendors in Aviation

Abstract Material characterization and assessment is a crucial stage in most of aviation and aeronautical research and a basis for further design and testing of more complex aircraft elements and structures. Material test’s reliability can only be guaranteed by conducting them at independent and reliable laboratories, operating based on a management system assessed by a third-party such as the accreditation according to the ISO / IEC 17025 or NADCAP or having the qualification of the second-party based on specific customer requirements. This paper introduces basic requirements for material testing laboratories according to accreditation systems and describes its responsibilities as qualified and reliable testing suppliers.

Microstructure evolution and interdiffusion behaviors of (Ni,Pt)Al coating with and without Re-diffusion barrier on IC21 substrate at 1100°C

The degradation of high temperature oxidation resistance and mechanical properties caused by the high temperature interdiffusion between the coating and the single crystal intermetallic superalloy substrate has become a heavily researched topic within aeronautical materials research in recent years. In order to study the microstructural evolution and interdiffusion behaviors of the coating and superalloy, the (Ni, Pt)Al coating with and without Re-diffusion barrier (Re-DB) was prepared on the Ni3Al based superalloy (Grade: IC21). The thermal exposure tests were carried out on the specimens in air at 1100 °C for 200 h. The results revealed that the Al content in the coating gradually reduced during thermal exposure, and both coatings underwent phase transformation from β-(Ni, Pt)Al to Ni3Al. The coating with Re-DB had a lower phase transformation ratio. Moreover, the coating with Re-DB had smaller and fewer TCP phases precipitated in the inter-diffusion zone (IDZ) and secondary reaction zone (SRZ), showing that the Re-DB contributed to a lower extent of interdiffusion. Based on the actual measured composition-distance data, the interdiffusion coefficients between the (Ni, Pt)Al coating and the IC21 substrate with and without Re-DB were determined using HitDIC software, which verified that Re-DB impeded the diffusion of Re, Mo and Cr from substrate to the coating.

SIBERIAN AERONAUTICAL RESEARCH INSTITUTE NAMED AFTER S. A. CHAPLYGIN 80TH ANNIVERSARY

The article describes the main stages of the creation of the Siberian Aeronautical Research Institute (SibNIA) named after S. A. Chaplygin from 1941 to the nowdays. The main works on aerodynamics and strength under normal conditions, at high and cryogenic temperatures of hypersonic aviation, rocket and space technology are presented. The issues of creating a composite aircraft TVS-2DTS, which is a modernization of the An-2 aircraft, are considered, and examples of restoration of aircrafts form the Great Patriotic War times are given.

Semi-Active Vibration Control Based on a Smart Exciter with an Optimized Electrical Shunt Circuit

A smart exciter coupled to cabin panels can be used as a new type of loudspeaker for emergency announcements in the aircraft cabin. The same device can also be used as a semi-active vibration control system which is effective in reducing the amplitude of structural vibration. The objective of this paper is to investigate the potential of vibration reduction using a smart exciter in combination with an optimized resistive-inductive shunt circuit, which serves as an absorbing network. First, the vibration reduction effect has been analyzed numerically using a simulation framework realized with COMSOL and MATLAB/Simulink. In a second step, the reduction effect of the smart exciter together with a resistive-inductive shunt circuit, which is produced by the Center of Applied Aeronautical Research (Zentrum für Angewandte Luftfahrtforschung GmbH, Hamburg, Germany), has been investigated experimentally. The results presented here prove that the smart exciter together with a resistive-inductive shunt can be highly effective in reducing structural vibrations.

Mapping the “Valley of Death”: Managing Selection and Technology Advancement in NASA's Small Business Innovation Research Program

In this paper, we determine the risk mitigation process inherent in managing a portfolio of technologies diverse in both their readiness for infusion and the nature of the performing organization, focusing on the so-called “valley of death” in which the technology's principles have been proven but prototypes have yet to be developed. Using the Technology Readiness Levels (TRLs) of projects funded by the National Aeronautics and Space Administration Small Business Innovation Research program, a two-stage competitive process, we find that the result of selection of the first round is a tendency toward larger companies. In the second round of funding, technology maturity is a stronger determinant of selection and company headcount is no longer a statistically significant driver. This combination allows the program to manage risk and deliver real technical advancement from even the smallest companies. We find that technologies typically advance from TRL 2, concept formulation, at the program's outset to roughly TRL 5, component validation, at the program's conclusion; these outcomes precede economic benefits from the subsidy. These findings illuminate a mechanism to address risk as well as demonstrating the technical outcomes of a managed early-stage technology program.

Improving the Satellite Power Supply Continuity using Flywheel Energy Storage System

Recently, Flywheel Energy Storage (FES) systems are gaining significant interest from National Aeronautics and Space Administration Glenn Research Center (NASA's GRC) in satellite applications due to their numerous advantages as an energy storage solution over the rest of the alternatives. Regarding FESS features such as high cycle life, long service life, high efficiency, high energy density and low environmental impact, this paper introduces a FESS management controller for use with the solar PV system in an integrated manner that ensures the continuity of the satellite power system and, thus, increases its efficiency. In addition, a prototype of the management control under various operating modes of the proposed unit is established. The satellite power supply management controller was implemented practically as a model using the Arduino controller. The practical results proved the continuity of the satellite operation in different operating modes using the FES system, which in turn would lead to improving the efficiency of the satellite feeding source compared to its performance using solar PV system only.

Compressor Degradation Management Strategies for Gas Turbine Aero-Engine Controller Design

The Advisory Council for Aeronautics Research in Europe (ACARE) Flight Path 2050 focuses on ambitious and severe targets for the next generation of air travel systems (e.g., 75% reduction in CO2 emissions per passenger kilometre, a 90% reduction in NOx emissions, and a 65% reduction in the noise emissions of flying aircraft relative to the capabilities of typical new aircraft in 2000). Degradation is an inevitable phenomenon as aero-engines age with significant impacts on the engine performance, emissions level, and fuel consumption. The engine control system is a key element capable of coping with degradation consequences subject to the implementation of an advanced management strategy. This paper demonstrates a methodological approach for aero-engine controller adjustment to deal with degradation implications, such as emission levels and increased fuel consumption. For this purpose, a component level model for an aero-engine was first built and transformed to a block-structured Wiener model using a system identification approach. An industrial Min-Max control strategy was then developed to satisfy the steady state and transient limit protection requirements simultaneously while satisfying the physical limitation control modes, such as over-speed, surge, and over-temperature. Next, the effects of degradation on the engine performance and associated changes to the controller were analysed thoroughly to propose practical degradation management strategies based on a comprehensive scientometric analysis of the topic. The simulation results show that the proposed strategy was effective in restoring the degraded engine performance to the level of the clean engine while protecting the engine from physical limitations. The proposed adjustments in the control strategy reduced the fuel consumption and, as a result, the emission level and carbon footprint of the engine.

Experimental noise source identification in a fuselage test environment based on nearfield acoustical holography

A major challenge in the subject of noise exposure in airplanes is to achieve a desired transmission loss of lightweight structures in the low-frequency range. To make use of appropriate noise reduction methods, identification of dominant acoustic sources is required. It is possible to determine noise sources by measuring the sound field quantity, sound pressure, as well as its gradient and calculating sound intensity by post-processing. Since such a measurement procedure entails a large amount of resources, alternatives need to be established. With nearfield acoustical holography in the 1980s, a method came into play which enabled engineers to inversely determine sources of sound by just measuring sound pressures at easily accessible locations in the hydrodynamic nearfield of sound-emitting structures. This article presents an application of nearfield acoustical holography in the aircraft fuselage model Acoustic Flight-Lab at the Center of Applied Aeronautical Research in Hamburg, Germany. The necessary sound pressure measurement takes one hour approximately and is carried out by a self-moving microphone frame. In result, one gets a complete picture of active sound intensity at cavity boundaries up to a frequency of 300 Hz. Results are compared to measurement data.

Probability Characteristics, Area Reduction, and Wind Directionality Effects of Extreme Pressure Coefficients of High-Rise Buildings

Wind tunnel tests are carried out for the Commonwealth Advisory Aeronautical Research Council (CAARC) high-rise building with a scale of 1:400 in exposure categories D. The distribution law of extreme pressure coefficients under different conditions is studied. Probability distribution fitting is performed on the measured area-averaged extreme pressure coefficients. The general extreme value (GEV) distribution is preferred for probability distribution fitting of extreme pressure coefficients. From the comparison between the area-averaged coefficients and the value from GB50009-2012, it is indicated that the wind load coefficients from GB50009-2012 may be non-conservative for the CAARC building. The area reduction effect on the extreme wind pressure is smaller than that on the mean wind pressure from the code. The recommended formula of the area reduction factor for the extreme pressure coefficient is proposed in this study. It is found that the mean and the coefficient of variation (COV) for the directionality factors are 0.85 and 0.04, respectively, when the orientation of the building is given. If the uniform distribution is given for the building’s orientation, the mean value of the directionality factors is 0.88, which is close to the directionality factor of 0.90 given in the Chinese specifications.

The Black Box That's Round and Red [Past Forward

Summary form only given, as follows. Problem: In the 1950s, major air disasters were on the rise, but determining the cause was often nearly impossible. Solution: Fit aircraft with a sturdy device that records cockpit conversation for recovery after a crash. Today the flight data and voice recorder seems like an obvious invention, but when David Warren first proposed it at Australia’s Aeronautical Research Laboratories in 1954, his boss flat out rejected it. It took four years for his idea to gain traction, and another five years before Australia became the first country to require the recorders on all aircraft. The modern-day equivalent remains a key tool for crash investigators. Though it’s often called the black box, it has always been a brightly colored orange or red to make it easier to find.

Multi-degree-of-freedom liner development: Concept to flight test

The emphasis on increased turbofan fuel efficiency requires advanced turbofan designs that will integrate higher engine bypass ratios and shorter nacelles. The resulting acoustic signature of these designs will have a more broadband character as well as a smaller available area for liner installation. This two-fold impact compels a need for an improvement in the state of the art in liner technology. Increasing the acoustic absorption efficacy over a broader frequency range is a means to address this need. An acoustic liner development and optimization process was conceived and employed to achieve and demonstrate an improved broadband liner design concept. A series of increasing technology readiness level liner studies were conducted to enhance the optimization methodology while validating the concept. This progression spanned several NASA Aeronautics Research Mission Directorate programs/projects due to its relevance. This article reviews the development and evaluation process of the multi-degree-of-freedom liner technology concept from formation through simple experimental models to a flight test over an approximate 10-year period, focusing on the discrete tests comprising the development.

Refined Mathematical Models for Across-Wind Loads of Rectangular Tall Buildings with Aerodynamic Modifications

This paper aims to systematically study the across-wind loads of rectangular-shaped tall buildings with aerodynamic modifications and propose refined mathematic models accordingly. This study takes the CAARC (Commonwealth Advisory Aeronautical Research Council) standard tall building as a benchmark model and conducts a series of pressure measurements on the benchmark model and four CAARC models with different round corner rates (5%, 10%, 15% and 20%) in a boundary layer wind tunnel to investigate the across-wind dynamic loads of the typical tall building with different corner modifications. Based on the experimental results of the five models, base moment coefficients, power spectral densities and vertical correlation coefficients of the across-wind loads are compared and discussed. The analyzed results shown that the across-wind aerodynamic performance of the tall buildings can be effectively improved as the rounded corner rate increases. Taking the corner round rate and terrain category as two basic variables, empirical formulas for estimating the across-wind dynamic loads of CAARC standard tall buildings with various rounded corners are proposed on the basis of the wind tunnel testing results. The accuracy and applicability of the proposed formulas are verified by comparisons between the empirical formulas and the experimental results.

Large-Eddy Simulation of Variable Speed Power Turbine Cascade With Inflow Turbulence

Abstract Numerical results are presented from the National Aeronautics and Space Administration (NASA) Glenn Research Center's in-house turbomachinery code Glenn-HT applied to the variable-speed power turbine (VSPT) experiment at the NASA Transonic Turbine Blade Cascade Facility. The main goal of this paper is to implement a digital filtering method to generate turbulence upstream and a subgrid model (localized dynamic k-equation model (LDKM)) in the framework of large-eddy simulation (LES) in order to investigate the effect of inflow turbulence on the transition seen in the VSPT experimental data at the cruise condition (incidence angle of 40 deg and Tu = 0.5%, 5%, 10%, and 15%). Although the boundary layer on the suction side and pressure side of the blades is initially laminar due to favorable pressure gradient, the laminar flow can transition to turbulent flow past a separation zone on the suction side or by natural or bypass transition. This process determines the total pressure losses in the wake. Therefore, it is desirable to develop a reliable prediction tool to accurately capture the transition mechanism in blade rows operated under the conditions of low Reynolds number and at a variety of freestream turbulence conditions. Our numerical studies reveal that the location of separation is rather insensitive to the level of Tu; however, the effect of increasing Tu seems to be in reducing the size and ultimately suppressing the separation bubble. In addition, we performed spectral analysis to identify the peak frequencies in the region where the separation bubble is formed, which provides valuable insights into the transition/separation mechanism.