Tunnel Circuit Research Articles

Reactive acoustic liner design

Acoustic treatment to reduce fan noise levels in a wind tunnel circuit consists of fibrous materials such as fibreglass or rockwool. Open cell foam materials are also used as acoustic treatments. The acoustic treatments are conventionally applied at fan tail cone regions, tunnel walls along fan diffuser section, cross-legs, test section diffuser, and nozzle contraction areas. However, conventional treatments are not possible in cryogenic wind tunnels, since bulk absorber materials with required resistivity, when operating at cryogenic temperatures, are not available. One possible solution is to design reactive silencers tuned to dominant frequencies. One such approach was used as noise control technique so as to satisfy test section noise specifications. The sound power spectrum of the compressor at different speeds were evaluated. The estimated test section sound pressure levels showed noise reduction at two dominant frequencies were required. The acoustic treatment, therefore, resulted in a double layer reactive design tuned to the two dominant frequencies. The design process will be highlighted in the presentation. The final treatment details will also be presented.Acoustic treatment to reduce fan noise levels in a wind tunnel circuit consists of fibrous materials such as fibreglass or rockwool. Open cell foam materials are also used as acoustic treatments. The acoustic treatments are conventionally applied at fan tail cone regions, tunnel walls along fan diffuser section, cross-legs, test section diffuser, and nozzle contraction areas. However, conventional treatments are not possible in cryogenic wind tunnels, since bulk absorber materials with required resistivity, when operating at cryogenic temperatures, are not available. One possible solution is to design reactive silencers tuned to dominant frequencies. One such approach was used as noise control technique so as to satisfy test section noise specifications. The sound power spectrum of the compressor at different speeds were evaluated. The estimated test section sound pressure levels showed noise reduction at two dominant frequencies were required. The acoustic treatment, therefore, resulted in a double layer...

Tunnel FET Analog Benchmarking and Circuit Design

A platform for benchmarking tunnel field-effect transistors (TFETs) for analog applications is presented and used to compare selected TFETs to FinFET technology at the 14-nm node. This benchmarking is enabled by the development of a universal TFET SPICE model and a parameter extraction procedure based on data from physics-based device simulators. Analog figures of merit are computed versus current density to compare TFETs with CMOS for low-power analog applications to reveal promising directions for the system development. To illustrate the design space enabled by TFETs featuring sub-60-mV/decade subthreshold swing, two example circuits including a picopower common-source amplifier and an ultralow-voltage ring oscillator are demonstrated.

ESWIRP: European Strategic Wind tunnels Improved Research Potential program overview

“European Strategic Wind tunnel Improved Research Potential” ESWIRP was a project in the EU 7th Framework Program (FP7—Grant agreement no: FP7-227816), which was aiming at improving the performance capabilities of three strategic wind tunnels in Europe, by strengthening the cooperation between these wind tunnels in a new consortium. The research consortium members are Office National d’Etudes et de Recherches Aérospatiales (operating the S1MA as its largest sonic wind tunnel), German–Dutch wind tunnels [operating the large low-speed facility (LLF) as its largest low-speed wind tunnel], and European transonic wind tunnel (ETW) (operating its cryogenic wind tunnel). Together, these wind tunnels cover a wide range of experimental capabilities of relevance to civil aviation and aeronautical research in general. The project started in October 2009 for a period of 5 years. The European financial contribution was €7.2 million. The project consist of two major parts: (1) improvements to the testing infrastructure; and (2) the provision of wind tunnel access to research groups which do not usually have the means to access such large-scale test facilities. These topics also involved public dissemination and information activities. Although the tunnels covered in this project are of a complementary nature, the infrastructure activities were joined together, by a common representation of, and approach to, the tunnel performance characteristics. To this end, a generic model of a virtual wind tunnel was developed, enabling operators to assess the effect of the control parameters upon the testing conditions. The final aim of all participants was to provide the user community with an improved set of capabilities to test their innovative ideas. To provide better access to these three major wind tunnels, mainly research groups from European universities were contacted. The approach taken has included maximum transparency of the process and support of the researchers by the organizations responsible for the tunnels. In addition, when possible, we encouraged research groups to work together, to obtain the full benefit of economies of scale in research projects. ESWIRP responded to the targeted approach of the Integrating Activities of the FP7 Capacities Work Program: Networking activities, essentially focused around four topics: (1) organization of information campaigns, lectures and workshops to disseminate knowledge between the partners and future users. (2) Opening of a website for the consultation of wind tunnel standards. (3) Exchange of personnel between the Consortium partners, to foster the spread of good practices and the exchange of technical know-how. (4) Joint development of a reference wind tunnel parameter database. Trans-national access and/or testing services: after the call for proposals by the facility providers, groups of researchers had the opportunity to benefit from free wind tunnel services, including technical assistance to support the corresponding scientific research team(s). Joint research activities, innovative modeling of wind tunnels has helped designers to make better decisions, before the implementation of any novel hardware. Based on a generic finite volume type of modeling approach, the operational behaviour and the time-dependent flow quantities around the wind tunnel circuit have been simulated. Such model can be used, for example, to conceive and tune particular sub-system control laws, or explore the implications of hardware changes. Based on a common approach, dedicated models were developed for S1MA, LLF and ETW. The infrastructure improvements targeted the capability to obtain unsteady test data (with high accuracy) in the ETW, to improve the capability to simulate aircraft behaviour in ground effect in the LLF, and to establish a reliable closed-loop control of test Mach number in the S1MA wind tunnel. European Strategic Wind tunnels Improved Research Potential Program is European support for strategic wind tunnels, key research infrastructures in the development process of current and future aircraft. This is the first time that European authorities have given such support.

DNW innovations in wind tunnel testing: new moving belt system for Large Low\xa0speed Facility

The German-Dutch Wind Tunnels DNW is one of Europe’s most advanced and specialized organizations for wind tunnel testing. DNW’s 11 wind tunnels include subsonic, transonic and supersonic facilities, and provide experimental aerodynamic simulation capabilities to a global user community at large. DNW provides techniques for aerodynamic, aeroacoustic or aeroelastic simulations and tests of scaled models in a controlled environment. Its experimental simulation techniques capture the essence of the issues to be investigated. The Large Low speed Facility (LLF) in Marknesse (the Netherlands) is an industrial wind tunnel for the low-speed domain. It is a closed circuit, atmospheric, continuous low-speed wind tunnel with one closed wall and one configurable (slotted) wall test section and an open jet. Low speed means testing of aircraft in take-off and landing flight configurations and therefore DNW focusses its investments for the LLF on safety (ground proximity, powered and unpowered) and environmental issues (acoustics) related testing capabilities. Recent DNW-LLF upgrade programs focussed on ground proximity simulation (procurement of a new moving belt system) and reducing of wind tunnel circuit background noise level to improve its capabilities and market attractiveness. The main drive for the latter initiatives is a clear trend in aircraft characteristics, i.e. continuous reduction of aircraft noise levels. Funding support was provided by the Ministry of Economic Affairs (the Netherlands), the German Aerospace Center DLR and the European Commission through EU 7th Framework European Strategic Wind tunnels Improved Research Potential ESWIRP. The paper will further detail the various development steps taken for the new moving belt system and elaborate on the calibration activities conducted.

Numerical investigation of air flow in a supersonic wind tunnel

In the framework of TsAGI’s supersonic wind tunnel modernization program aimed at improving flow quality and extending the range of test regimes it was required to design and numerically validate a new test section and a set of shaped nozzles: two flat nozzles with flow Mach number at nozzle exit M=4 and M=5 and two axisymmetric nozzles with M=5 and M=6. Geometric configuration of the nozzles, the test section (an Eiffel chamber) and the diffuser was chosen according to the results of preliminary calculations of two-dimensional air flow in the wind tunnel circuit. The most important part of the work are three-dimensional flow simulation results obtained using ANSYS Fluent software. The following flow properties were investigated: Mach number, total and static pressure, total and static temperature and turbulent viscosity ratio distribution, heat flux density at wind tunnel walls (for high-temperature flow regimes). It is demonstrated that flow perturbations emerging from the junction of the nozzle with the test section and spreading down the test section behind the boundaries of characteristic rhomb’s reverse wedge are nearly impossible to eliminate. Therefore, in order to perform tests under most uniform flow conditions, the model’s center of rotation and optical window axis should be placed as close to the center of the characteristic rhomb as possible. The obtained results became part of scientific and technical basis of supersonic wind tunnel design process and were applied to a generalized class of similar wind tunnels.

Synergy of Wind Energy Harvesting and Synchronized Switch Harvesting Interface Circuit

Due to the complex aero-electro-mechanical coupling involved in wind energy harvesting systems, power enhancing efforts in the literature are mostly devoted to structural modifications while the interface circuit is simplified to a resistive ac load. Yet the ac outputs are not applicable for practical usage. In this paper, we study the dynamics and dc power generation of galloping energy harvester. In particular, the enhancement of wind power extraction using the synchronized switching harvesting on inductor (SSHI) power conditioning circuit is emphasized. Analytical solution of the steady-state mechanical and electrical responses with the SSHI interface is derived explicitly and validated with wind tunnel experiment and circuit simulation. The performance of SSHI interface is compared to that of a standard bridge rectifier interface circuit. It shows that the SSHI interface achieves tremendous power enhancement in a weak-coupling system, and higher wind speeds render more significant power enhancement. Moreover, given the same wind condition and output power requirement, a system connected to the SSHI uses much less piezoelectric material compared to that connected to the standard circuit. With a weak-coupling harvester operating at a wind speed of 7 m/s, the SSHI can harvest up to 143% more wind power than the standard circuit.

Neural Network Based on SET Inverter Structures: Neuro-Inspired Memory

This paper presents a basic block for building large-scale single-electron neural networks. This macro block is completely composed of SET inverter circuits. We present and discuss the basic parts of this device. The full design and simulation results were done using MATLAB and SIMON, which are a single-electron tunnel device and circuit simulator based on a Monte Carlo method. Special measures had to be taken in order to simulate this circuit correctly in SIMON and compare results with those of SPICE simulation done before. Moreover, we study part of the network as a memory cell with the idea of combining the extremely low-power properties of the SET and the compact design.

Numerical study of the injection process in a transonic wind tunnel: The numerical details

Numerical prediction of an injection process was successfully performed. The physical problem corresponds to the mixing of a number of parallel supersonic jets with a subsonic main stream, in the presence of solid walls. In practice, this arrangement is to be used as a boosting device in a transonic wind tunnel, with the ultimate objective of extending the tunnel’s envelope without penalizing the main compressor. Five supersonic nozzles are installed at the floor and five at the ceiling of the transition module’s entrance section. Due to the great difference between cross-sectional typical lengths of nozzles and tunnel, the numerical tool has to have a three-dimensional capability. The core of the code is an adaptation of the finite-difference diagonal algorithm, and turbulence effects are properly tackled by the use of the Spalart and Allmaras one-equation scheme. Some simplifications were adopted in order to render the problem minimally tractable, especially in this initial numerical simulation stage, which is the reporting objective of this article. Albeit this, and due to the magnitude of the problem in hand, these simplifying initiatives were not sufficient to bring the calculations down to a scale of reasonable computer costs. Hence, a sequence of grids, coupled with a division of the computational domain, was adopted. Boundary conditions were thoroughly worked, especially the ones related to the domain of calculation’s entrance plane. This plane is important because of the many viscous gradient regions that project against it. Among the many settings under which a tunnel can operate there is one defined as the “design condition”, or else as the “design point”, as it is sometimes called. For a tunnel equipped with an injection system, the design point asks (besides many other specifications) for equal static pressures at the section where the supersonic jet meets for the first time the main stream coming from the tunnel circuit. We have simulated five different operating settings of the tunnel and among them the design condition. Therefore, we have results for the design as well as for many off-design points. The idea was to simulate the many tunnel settings and also to test the code’s ability to handle all these different situations. The code was duly validated and verified, and in the sequel the steady flow field in the mixing region was calculated. Many interesting and very important results were obtained, among which we would point out the existence of compression and expansion domes at the supersonic regions, the calculation of the many engineering parameters related to the injection process, and especially the determination of the injection’s gain threshold.

Balancing a four-branch–single-molecule nanoscale Wheatstone bridge

Using the extended Hückel molecularorbital–Nelastic scattering quantum chemistry technique, the scattering electronicproperties of four-and two-electrode monomolecular Wheatstone bridges arediscussed. Simple intramolecular circuit rules are given for the design of anintramolecular electronic circuit integrated in a single molecule. The balancingcondition of the four-electrode monomolecular Wheatstone bridge is provided.The value of the tuning resistance of the bridge is the same applyingthe new tunnel circuit rules and the standard Kirchhoff node and meshlaws. Only the way of reaching the equilibrium of the bridge is different.

Intramolecular circuits connected toNelectrodes using a scattering matrix approach

The scattering matrix technique is extended to describe the electronic transport characteristics of intramolecular circuits driven in a ballistic or a tunnel transport regime. The circuit is assumed to be connected by N electrodes, As a working example, the electronic properties of a T-node circuit are presented leading to the design of an OR logic gate working in a ballistic regime. In the tunnel regime, only the node' Kirchhoff law of circuit remains valid at the nodes of an intramolecular tunnel circuit and the electronic characteristics of the branches composing the circuit are mutually independent. It results in a difficult design of a logic OR intramolecular gate of high performance and stability, pointing out the urge for new architectures to implement complex logic functions inside a single molecule.

Prediction of transients and control reactions in a transonic wind tunnel

This work describes a lumped parameter mathematical model for the prediction of transients in an aerodynamic circuit of a transonic wind tunnel. Control actions to properly handle those perturbations are also assessed. The tunnel circuit technology is up to date and incorporates a novel feature: high-enthalpy air injection to extend the tunnel’s Reynolds number capability. The model solves the equations of continuity, energy and momentum and defines density, internal energy and mass flow as the basic parameters in the aerodynamic study as well as Mach number, stagnation pressure and stagnation temperature, all referred to test section conditions, as the main control variables. The tunnel circuit response to control actions and the stability of the flow are numerically investigated. Initially, for validation purposes, the code was applied to the AWT (Altitude Wind Tunnel of NASA-Lewis). In the sequel, the Brazilian transonic wind tunnel was investigated, with all the main control systems modeled, including injection.

STATUS OF IMPROVING NAL 0.2M SUPERSONIC WIND TUNNEL FOR QUIET FLOW

Some features of the 0.2m supersonic wind tunnel at National Aerospace Laboratory relating to the quiet flow establishment are described. Pressure fluctuations were measured along the tunnel circuit. The pressure fluctuation ratio at the settling chamber exit satisfies a goal of the value less than 0.2 % for the quiet wind tunnel. However, the measured velocity fluctuation ratio does not satisfy another goal of the value less than 1 %. Measured Pitot pressure fluctuation ratio at the test section does not satisfy a goal of the value less than 0.1 % for the quiet flow although the value is near the goal.

SIMON-A simulator for single-electron tunnel devices and circuits

SIMON is a single electron tunnel device and circuit simulator that is based on a Monte Carlo method. It allows transient and stationary simulation of arbitrary circuits consisting of tunnel junctions, capacitors, and voltage sources of three kinds: constant, piecewise linearly time dependent, and voltage controlled. Cotunneling can be simulated either with a plain Monte Carlo method or with a combination of the Monte Carlo and master equation approach. A graphic user interface allows the quick and easy design of circuits with single-electron tunnel devices. Furthermore, as an example of the usage of SIMON, we discuss the essential problem of random background charge and present possible solutions.

138 解説風洞実験概論

Wind tunnel testing in general is described for those who are not familiar with this field of engineering. Wind tunnels are grouped according to the testing speeds, test section geometry and configurations, and tunnel circuit shapes. Similality laws of and problems in wind tunnel testings are presented. Types of testings conducted in wind tunnels are described. The future of wind tunnel testing is briefly discussed.

Effect of longitudinal riblets on axisymmetric body drag

The results of comparative gravimetric measurements of the total drag on an axisymmetric body with a smooth and ribbed cylindrical surface are described. The experiments were carried out in a closed wind tunnel at initial tunnel circuit pressures equal to 0.5 and 1 absolute atmosphere with artificially generated model boundary layer turbulence. The free-stream Mach number was varied on the range from 0.15 to 0.85, the Reynolds number Re, calculated from the model length, on the range 4·106–30·106, and the angle of attackα on the range from 0 to 12°. The maximum total drag advantage obtained with the ribbed model was 8%. A significant fraction of the drag reduction achieved may be associated with the effect of the ribbing on the drag created by the smooth tail of the body.

Slotted-wall blockage corrections for disks and parachutes

Bluff shapes, including parachutes, often require large blockage corrections when tested in solid-wall wind tunnels. The magnitude of the correction is much smaller in test sections with slotted walls, but the blockage becomes a complicated function of model size, wall porosity, and upstream and downstream boundary conditions. Disk and parachute models were tested in a low-speed wind tunnel where the slotted-wall open area ratio and model axial position were systematically carried. In steady flow, the benefit of the wall slots was achieved asymptotically as the models were moved downstream from the leading edge of the slots, and this flow development length increased with decreasing wall porosity and increasing model size. The experiments with the parachutes provided the first quantitative information on wall interference and tunnel circuit response during the nonsteady inflation process. There was no observable block age effect during the inflations with any of the slotted-wall configurations studied.

The high speed water tunnel facility at the Indian Institute of Science

The present article about the high speed water tunnel facility at the Indian Institute of Science, Bangalore, provides a general description of the tunnel circuit, and brief reports on the performance of the facility and some typical results from investigations carried out in it. A unique aspect of the facility is that it has a horizontal resorber in the form of a large cylindrical tank located in the lower leg of the circuit. The facility has been used, among other things, for flow visualization studies, and investigations on marine propeller hydrodynamics and “synthetic cavitation”. The last topic has been primarily developed at the Indian Institute of Science and shows considerable promise for basic work in cavitation inception and noise.

Lower limit for the velocity fluctuation level in wind tunnels

The origins of the velocity fluctuations in the test section of a wind tunnel are discussed. Vorticity (turbulence converted from upstream) can be reduced by a careful design of the settling chamber to almost any desired level. The amplitudes of pressure waves propagating round the tunnel circuit can also be reduced considerably. The lowest levels of the velocity fluctuations in wind tunnels are determined by those pressure fields that are created on the outer boundaries of the test section. These boundaries are the free shear layers in the case of free jet facilities and the turbulent boundary layers in the case of closed wall test sections. The lower limit for the rms velocity level is achieved in many open jet wind tunnels (typically 0.15%). The corresponding limit for low speed tunnels with closed test sections is smaller by a factor of at least twenty but not yet known.

The application of cryogenics to high Reynolds number testing in wind tunnels. Part 1: Evolution, theory, and advantages

An improved way to increase the Reynolds number capability of wind tunnels has been developed in the United States at the NASA Langley Research Center through the application of cryogenic technology. Cooling the test gas in the wind tunnel to cryogenic temperatures by spraying liquid nitrogen into the tunnel circuit increases the test Reynolds number by as much as a factor of 7 with no increase in dynamic pressure and with a reduction in drive power. Part 1 of this two-part review covers the evolution, theory, and major advantages of cryogenic wind tunnels. Part 2 will describe the development and early application of the cryogenic wind tunnel concept in the United States and some of the major cryogenic wind tunnel activities around the world, the most significant of which is a large fan-driven transonic cryogenic tunnel recently completed at the Langley Research Center.

Design and capabilities of a novel cylindrical-post magnetron sputtering source

A cylindrical-post magnetron sputtering source is described in which the paths of the magnetic confinement tunnel and entrapped electron drift circuit extend along the cylindrical axis. Then (and only then) can the associated sputtering discharge be scanned circumferentially over the target by rotating the generating magnet within the cylindrical cathode. The design of a basic magnet for this purpose is given which can have any desired length of extension and consequent uniform target erosion and sputter emission of coating material from a cylindrical cathode. From the variations in discharge voltage and deposition rate with applied current for a cylindrical magnetron operating with such a rotating magnet, it is concluded that the trapping of secondary electrons is nearly complete and the energy efficiency of sputtering emission corresponds closely to the theoretical limit. Measurements of the magnetic field, deposition rate, probe potential, heating flux and film stresses as functions of the angle around a stationary (non-rotating) magnet reveal that the emission of coating material, electrons and energetic particles from such a source is markedly directional, although these effects are time averaged by rotation during normal operation. Finally, an advanced spiral discharge is shown, which incorporates the same basic principle of axial extension of the magnetic tunnel and electron drift circuit but accomplishes spatial as well as time averaging of the sputtered flux to a given substrate.