Aerodynamic Test Facility Research Articles

Ceramic and Metal Additive Manufacturing of Monolithic Rotors From SiAlON and Inconel and Comparison of Aerodynamic Performance for 300W Scale Microturbines

Abstract The gas turbine industry is continuously developing and testing new materials and manufacturing methods to improve the performance and durability of hot section components, which are subjected to extreme conditions. SiAlON and Inconel 718 are especially desirable for turbomachinery applications due to their high strength and high-temperature capabilities. To demonstrate the viability of additive manufacturing for small-scale turbomachinery for 300W scale microturbines, a monolithic rotor with a design speed of 450,000 RPM containing radial turbine and compressor was developed considering additive manufacturing constraints. The geometry was manufactured from SiAlON and Inconel 718 using lithographic ceramic manufacturing and selective laser melting, respectively. The additive manufacturing and thermal process parameters as well as material characterization are described in detail. Surface and computerized tomography scans were conducted for both rotors. While the metallic rotor showed undesirable printing artifacts and a large number of defects, the ceramic part achieved a level of relative precision and surface quality similar to large-scale production via casting. To compare turbomachinery performance, an aerodynamic test facility was developed allowing to measure pressure ratios and efficiency of small compressors. The rotors were tested in engine-realistic speeds, achieving a compressor rotor pressure ratio of 2.2. The ceramic part showed superior efficiency and pressure ratio compared to the Inconel rotor. This can be explained by lower profile and incidence losses due to a higher fidelity physical representation of the model geometry and better surface finish.

The Ford Rolling Road Wind Tunnel Facility

<div class="section abstract"><div class="htmlview paragraph">The Ford Motor Company Rolling Road Wind Tunnel (RRWT) is a state-of-the-art aerodynamic wind tunnel test facility in Allen Park, Michigan. The RRWT has operated since January 2022 and is designed for passenger and motorsport vehicle development. The test facility includes an office area, three secure customer vehicle preparation bays, a garage area, a vehicle frontal area measurement system, and a full-scale ¾ open jet wind tunnel. The wind tunnel features an interchangeable single belt and 5-belt Moving Ground Plane (MGP) system with an integrated 6-component balance, a two-position nozzle, boundary layer removal systems, and two independent flow traverse systems. Each flow traverse has a large horizontal box beam and vertical Z-strut that can position the flow traverse accurately within the test volume. The individual traverse systems can also operate in tandem and have the capability to perform stereo PIV measurements and scale model vehicle testing, including vehicle passing or drafting simulations. The MGP can be quickly changed between single belt and 5-belt operations, requiring only a single eight-hour shift to transition between the two configurations. The efficient wind tunnel airline is capable of airspeeds up to 250 km/h in the large 26.4 m<sup>2</sup> nozzle configuration and 322 km/h in the small 18.6 m<sup>2</sup> nozzle configuration using a 12-blade, 8 m diameter fan with a 5.4 MW motor. The wind tunnel’s flow quality and aerodynamic performance compare well with similar facilities in the automotive industry. Ford Motor Company is currently correlating aerodynamic measurement data from the RRWT with other similar facilities, using 60 vehicles across multiple product lines.</div></div>

Simultaneous measurement of pressure and temperature in a supersonic ejector using FBG sensors

In this work, we have demonstrated the use of fiber Bragg grating (FBG) sensors for simultaneous measurement of wall static pressure and temperature in a supersonic ejector. Supersonic ejectors are ground-based high-speed aerodynamic test facilities characterized by harsh conditions, such as high pressure and temperature gradients. An FBG-based sensor setup was developed consisting of a pressure measuring bare FBG and a specially designed pressure-insensitive FBG temperature probe that can be mounted on the wall of the supersonic ejector. The FBG temperature probe was used for temperature measurement as well as temperature compensation of the pressure measuring FBG sensor. Wall static pressure measurements in the supersonic ejector were carried out at different tank pressures and Mach number flows. The FBG pressure measurements were validated with those of standard piezoresistive-based sensor measurements. Both responses were found to match closely, with FBG sensors having a faster response time and higher pressure resolution. Fluid structure interaction simulation was carried out in Comsol Multiphysics to understand the interaction of high-speed turbulent flow with FBG sensor. The FBG strain profile due to flow-induced stress and its dependence on flow pressure was studied. A detailed analysis of the effect of preceding fiber length on FBG pressure measurement was carried out. FBG sensors, due to their miniature size, ability to withstand harsh environments and multi-parameter sensing capability, can be used in ground-based aerodynamic test facilities with minimal intrusion into the flow.

Studying the Swirl Flow Hydrodynamics in the Guiding Channel Area Downstream of Mixing Spacer Grids of a PWR Reactor Fuel Assembly

The results from studying the coolant flow in fuel assemblies downstream of mixing spacer grids of a PWR reactor are presented. The aim of the study is to estimate the effect from using different designs of mixing grids. For this purpose, experimental investigations were carried out on an aerodynamic test facility with scaled models of fuel assembly fragments containing mixing spacer grids of different designs. Two adjacent cells of the guiding channel zone were selected as the representative study area. The specific structural feature of these cells is that the turbulizers installed on the intensifying grids have different spatial orientation. The general flow pattern is represented by the vector fields of tangential velocities and by the distribution of relative velocities in the gaps between the fuel rods and the guiding channel. For estimating the effect from using the grid designs with respect to coolant flow mixing, the intracell vortex formation coefficients and intercell mixing coefficients were analyzed. It has been shown from the performed analysis that, owing to the use of the alternative design with a pair of cell deflectors oriented in a changed direction, the intercell transfer coefficient and the intracell vortex formation coefficient were increased by a factor of 1.13 and 2.2, respectively, in comparison with those in the basic design. Hence, the use of the grid of the alternative design is more preferable for obtaining better mixing of the coolant flow. The accumulated database on coolant flow in the Square FA serves for engineering substantiation of the PWR reactor cores. The results from experimental studies are used for verification of CFD codes developed both in Russia and abroad and of programs for detailed cell-wise analysis of the cores for reducing the conservatism in substantiating their thermal reliability.

Reproduction of air velocity in the entrance region of the test pipe in a wind tunnel

The airflow development in the pipe, in the entrance region of the wind tunnel located in the Lithuanian Energy Institute, the laboratory of Heat Equipment Research and Testing is investigated to analyze the conditions for the reproduction of air velocity values. The analysis is performed to reveal undeveloped flow conditions where the calibration of the devices is usually made, the entrance region of the pipes, or free stream from the nozzles. In this study, different flow regimes have been investigated using different air velocity measurement methods. Experimental and numerical results clearly show the features of the developing flow. They both demonstrate the stable core of the velocity profile up to 5 D in the pipe and ≤1 D from the entrance into the free stream in the testing chamber. Ultrasonic anemometer (UA) installed in the aerodynamic test facility shows reliable and highly comparable results with another non-intrusive device – laser Doppler velocimeter (LDA) in a range of velocities from 0.05 m/s up to 30 m/s. UA integrated into the wind tunnel is not found to be used for metrological issues for air velocity. Due to the fast response, they both enabled to analyze fluctuations in the flow. Local vortices identified in the flow have influenced the low-frequency fluctuations and the scatter of measurement results. Moreover, high-frequency fluctuations found in the flow originated from the flow turbulence and might be due to the electronic or acoustic noise. The stabilization of the entrance region in the pipe influences the mean value of air velocity, the transversal distribution of velocity and the development of axial velocity in different test sections of the pipe in a wind tunnel. Along with the recirculation zones in cavities of ultrasonic transducers, these factors are essential that make an impact on the reproduction of air velocity value.

Hydrodynamic Features of the Flow Downstream from the Mixing Spacer Grid in a Kvadrat Fuel Assembly in PWRs

The experimental investigation of local hydrodynamic characteristics of the coolant flow downstream of a mixing spacer grid (MSG) in characteristic regions of a Kvadrat fuel assembly in PWRs was performed. The importance of this investigation is due to the fact that MSGs of interest can enhance heat-and-mass transfer. Finding the best design of the grid is required for corroboration of the thermal engineering reliability and operability of the PWR core. The paper presents a description of the test facility and a model of a fuel assembly fragment, the investigation procedure, and discussion of the results. The experiments were performed in the aerodynamic test facility on a scaled model of a fragment of a Kvadrat fuel assembly by simulating the water coolant flow using an air flow according to the hydrodynamic similarity theory. Within the scope of the investigation, the transverse velocity fields in the coolant flow were studied in the characteristic cross-sections of the fuel assembly. The transverse velocity distribution was measured with a five-channel pneumometric probe that can determine the module and direction of a flow velocity vector at an investigated point. The experimental results are presented in the form of distribution of relative transverse velocity downstream of MSG in the characteristic regions of the fuel assembly, such as standard cells, guide channel, and a gap between fuel rods. Based on the experimental data, the coolant flow features have been revealed, and the regularities in the development of transverse velocity field downstream of the mixing spacer grid under investigation have been determined. These experimental data are required for assessment of the mixing spacer grid effectiveness, verification of 3D CFD-programs, and applicable cell-by-cell codes for calculation of a PWR core with a Kvadrat fuel assembly.

Experimental studies of local coolant hydrodynamics using a scaled model of cassette-type fuel assembly of a KLT-40S reactor

The results of experimental studies of local hydrodynamic and mass exchange characteristics of the coolant flow behind the spacer grid in the fuel assembly of a KLT-40S reactor are presented. The experiments were aimed at the investigation of representative domains of the fuel assembly with three tracer injection regions. The studies were performed at the aerodynamic test facility using the tracer gas diffusion method. According to the theory of hydrodynamic similarity, the obtained experimental results can be transferred to full-scale coolant flow conditions in standard fuel assemblies. The analysis of the tracer concentration propagation made it possible to determine in detail the flow pattern and find the main regularities and specific features of the coolant flow behind the plate spacer grid of KLT-40S fuel assembly. The hydraulic resistance coefficient of the spacer grid was experimentally determined. The coefficients of mass exchange between cells for representative cells of the displacer region in the KLT-40S fuel assembly were calculated for the first time; these results are presented in the form of the “mixing matrix.” The results of studies of local coolant flow hydrodynamics in the KLT-40S fuel assembly are used at AO Afrikantov OKBM for estimation of thermotechnical reliability of active cores for reactors of floating nuclear power stations. The experimental data on hydrodynamic and mass exchange characteristics are included in the database for verification of CDF codes and detailed cell-wise calculation of the active core for KLT-40S reactor installation. The results of these studies can be used at FSUE RFNC-VNIIEF for testing and verification of domestic three-dimensional hydrodynamic CFD codes (“Logos”) that are applied for substantiation of newly designed reactor installations. Practical recommendations on the application of the obtained results in thermohydraulic calculations of the active core for the KLT-40S reactor will be worked out. Proposals on further improvement of structural elements of active cores in the considered nuclear power installations will also be presented.

벨마우스와 레이크를 이용한 대용량 유량 계측

공력학적 성능을 평가하는 대형 유동 시험장치에서 시험체 입구로 들어가는 유체의 압력, 온도, 유량등은 시험체의 성능 계산에 필수적인 항목이므로, 이 값들을 정확하게 측정하는 것이 중요하다. 본 논문에서는 벨마우스와 레이크를 사용하여 보정 유량 범위가 5 ~ 8 kg/s인 대용량 유량을 계측하는 방법을 연구하였다. 벨마우스는 ISO Standard를 따라 0.5% 정확도를 만족할 수 있도록 설계하였고, 레이크는 등면적으로 배치하도록 설계하였다. 총 9 회의 서로 다른 조건의 시험을 분석한 결과 레이크 레이놀즈 수와 유량값의 비가 1차 함수 관계에 있음을 확인하였고, 이 관계식을 이용하여 레이크의 유량값을 벨마우스의 값을 기준으로 최대 -0.507%, 평균 -0.000274% 오차율로 보정할 수 있었다. For an aerodynamic test facility, it is very important to get the precise measurement data of pressure, temperature and mass flow rate at the upstream to the test article. Hence, a new measurement method using a bellmouth and rakes was studied for the large scale system of which the corrected mass flow is between 5 kg/s and 8 kg/s. The bellmouth was designed by ISO standard for 0.5% accuracy, and the rakes were designed by using the equal area method. From the results of 9 test trials, it is found that the Reynolds number of rakes and the mass flow rate ratio can be simply formulated by an one-dimensional equation. The mass flow rate of rakes was calibrated by this equation. By the result of calibration, The maximum error rate was -0.507%, and the average error rate was -0.000274%.

The application of active control for turbocharger turbines

In this paper, the motivation behind the development of an active control turbocharger is presented, along with the initial thinking that led to the basic concept of applying active flow control at the inlet to a turbocharger turbine. In addition, the concept of active control for turbochargers is analysed in depth with the purpose of presenting a theoretical basis for any subsequent application of this type of control of exhaust gas flow into a turbocharger turbine by providing the fundamental thermo-fluids background. Secondly, the aim was not only to merely present a theory summarising the behaviour of the exhaust gas flow occurring during turbocharger turbine inlet geometrical changes, but to also present the implications from the periodic nature of these geometric changes, in particular with respect to cycle performance results both for the turbocharger and for the engine. The effects of the application of active control turbochargers were demonstrated through testing of the first prototype active control turbocharger built and tested at the aerodynamic test facility at Imperial College and through the experimental data collected. In this first attempt, at the most favourable amplitudes tested, the power recovered reached a maximum value of 7.5% increase over the equivalent variable geometry turbocharger performance, although this depended on the phasing of the turbine inlet area variation in relation to the energy content variation of the incoming exhaust pulse.

A Marine Propeller Aerodynamic Test Facility

Abstract: Conventional propeller test facilities such as tow tanks, cavitation tunnels and the open sea have various limitations such as cost, accessibility, size and accuracy. An aerodynamic marine propeller test facility has been developed at the University of British Columbia to allow for performance evaluations of full‐size marine propellers in the highly controlled environment of a wind tunnel. Thorough static and dynamic calibrations of the test rig confirmed that the sensors have a highly linear response with essentially zero crosstalk between the thrust and torque signals. Performance curves acquired from a commercial 24 × 24 propeller show that the repeatability error of the torque and thrust measurements is <1%. The uncertainties of the advance ratio, torque coefficient, thrust coefficient, and efficiency are 0.2%, 0.5%, 0.1%, and 1%, respectively. Performance curves measured over a range of the Reynolds numbers show that Reynolds number independence is achieved for Reynolds numbers above approximately 5 × 105.

PIV application in advanced low reynolds number facility

The advent of micro aerial vehicles (MAV) and advanced flow control methods, using microelectromechanical systems (MEMS) and micro-blowing or suction, has significantly increased the need for a better understanding of very low Reynolds number flows. Aerodynamic testing in this flow regime using conventional facilities, such as wind or water tunnels, is seriously hampered by the necessary small model sizes and low testing speeds, rendering it very difficult to diagnose the flow with adequate spatial resolution and to measure aerodynamic loads with sufficient accuracy. A proof-of-concept pilot of a novel facility specifically intended for low Reynolds number testing has been built and is briefly described. It is based on the use of a high kinematic viscosity test medium, which allows testing superscale models at the correct Reynolds number. The facility is akin to a towing tank, but does not have a free surface with its associated shortcomings. Implementation of the particle image velocimetry (PIV) technique in this type of facility is complicated by the fact that the optics, rather than being stationary as is the case in conventional aerodynamic testing facilities, move in synchronism with the model. Mistracking directly results in velocity-field errors which must be corrected. Methods to do so are described.

Development of a Nearly Omnidirectional Velocity Measurement Pressure Probe

The development of a nearly omnidirectional pressure probe for three-velocity-component and pressure measurements is described, focusing on the techniques employed in probe fabrication, calibration, and frequencyresponse study. The probe tip is a sphere with 18 pressure ports properly distributed over the spherical surface. The device eliminates the velocity directionality limitations of current multihole probes and constitutes a rugged tool for use in complex three-dimensional e ow mapping. An automated calibration system was used to generate a probe calibration database of approximately 10,000 individual probe orientations. Least-squares-based and neural-network-based calibration algorithms were developed. The reliability of the calibration procedures and algorithms is demonstrated e rst. Then probe utility is demonstrated in a e owe eld with e ow reversal, downstream of a backward-facing step. Last, a study of the probe frequency response is presented. I. Introduction T HE design, evaluation, and optimization of complex aerodynamicgeometriesinvolveextensivewind-tunneltestingand/or computationally intensive numerical simulations. Even in the latter case, high-quality experimental wind-tunnel results with minimal, quantie able errors are still necessary for code-validation purposes. Moreover, in aerodynamic testing facilities where large volumes of data need to be acquired in tight schedules, downtime due to poor instrumentation performance is highly undesirable. Such facilities include industrial testing wind tunnels, as well as high-productivity computational e uid dynamics code validation facilities. 1 In such environments, e ow measurement techniques such as laser Doppler velocimetry and particle image velocimetry, although powerful, usually require painstaking efforts toward their successful usage. Costly components; complex setups; troublesome e ow seeding requirements; lack of e exibility, ruggedness, and mobility; and ease of misalignment often render such techniques impractical. Moreover, in testing of complex three-dimensional geometries, accessibility of the entire e owe eld around the model is an essential issue. When employing optical techniques, large sections of the e owe eld are obstructed optically by the presence of the model. To access such regions, repositioning of the instrumentation setup is necessary, a time-consuming process with the associated potential pitfalls. Multihole pressure probes 2‐7 in many cases have provided the easiest-to-use and most cost-effective method for three-component e ow velocity measurements in research and industry environments. However, even with expanded measurement capabilities of such instruments, the current pressure probe cone gurations and techniques have a limited range of velocity inclinations that they can measure. The velocity inclination is indicated as the cone angle µ in Fig. 1. Let µmax be the maximum cone angle that can be measured reliably by the probe. In other words, a probe with a µmax of 40 deg can accurately measure any velocity vector that is contained within a cone with its apex at the probe tip, its axis along the probe axis, and with an apex included angle of 80 deg (Fig. 1). Measurable cone angles as high as 75 deg are not uncommon for seven-hole probes. 7 Following this reasoning, an omnidirectional probe is a probe that has a cone angle of 180 deg (360 deg included angle ); i.e., it can measure any velocity vector regardless of its orientation. The present work describes the development of a nearly omnidirectional probe that can measure up to cone angles of 170 deg

Measurement capabilities of planar Doppler velocimetry using pulsed lasers

Analytical models of a spectral filter that contains iodine vapor and of the noise sources associated with charge-coupled-device (CCD) detector technology are combined with a planar Doppler velocimetry (PDV) signal analysis to evaluate the measurement capabilities of PDV for quantitative aerodynamic research and production wind-tunnel testing applications. The criteria for optimizing the filter cell and calibrating the frequency scale of its transmission function are described. The measurement uncertainty limits owing to scientific-grade CCD detector performance are then evaluated, and an analysis is developed of the scattering properties of aerosols suitable for aerodynamic flow seeding. The combined results predict that single-pulse PDV measurements with velocity measurement uncertainties as small as 2 m/s should be possible in aerodynamic test facilities for measurement distances of tens of meters.

Progress in laser spectroscopic techniques for aerodynamic measurements - An overview

An overview is given of the capabilities and recent progress in laser-spectroscopic measurement techniques for use in aerodynamic test facilities and flight research vehicles. It includes a survey of the literature which is centered on this application of laser spectroscopy. The intended reader is the specialist in experimental fluid dynamics who is not intimately familiar with the physics or applications of laser spectroscopy. Thus, some discussion is also included of the nature of each laser-spectroscopic technique and the practical aspects of its use for aerodynamic measurements. The specific techniques reviewed include laser absorption, laser-induced fluorescence, laser Rayleigh scattering, and laser Raman scattering including spontaneous and coherent processes.

Simulation tests for temperature mixing in a core bottom model of the HTR-Module

Interatom and Siemens are developing a helium-cooled Modular High Temperature Reactor. Under nominal operating conditions temperature differences of up to 120°C will occur in the 700°C hot helium flow leaving the core. In addition, cold gas leakages into the hot gas header can produce even higher temperature differences in the coolant flow. At the outlet of the reactor only a very low temperature difference of maximum ±15°C is allowed in order to avoid damages at the heat exchanging components due to alternating thermal loads. Since it is not possible to calculate the complex flow behaviour, experimental investigations of the temperature mixing in the core bottom had to be carried out in order to guarantee the necessary reduction of temperature differences in the helium. The presented air simulation tests in a 1:2.9 scaled plexiglass model of the core bottom showed an extremely high mixing rate of the hot gas header and the hot gas duct of the reactor. The temperature mixing of the simulated coolant flow as well as the leakage flows was larger than 95%. Transfered to reactor conditions this means a temperature difference of only ±3° C for the main flow at a quite reasonable pressure drop. For the cold gas leakages temperature differences in the hot gas up to 400°C proved to be permissible. The results of the simulation experiments in the Aerodynamic Test Facility of Interatom permitted to design a shorter bottom reflector of the core.

Technique for aerodynamic force measurement within milliseconds in shock tunnel

For aerodynamic force measurement in shock tunnels and similar short duration aerodynamic testing facilities we have developed a novel measurement technique. Its key feature is a mounting support, which releases the test model and grips it again after a free flight duration of about 10 milliseconds. The model is equipped with small accelerometers and may contain additional installations. The short free flight allows the use of thin wires because the model travels only a few millimeters during this time. Validation experiments with a cone-cylinder of known drag coefficient show good accuracy with a response time of about half a millisecond. Pitot pressure measurement and suitable data processing allow for direct evaluation of aerodynamic coefficients in slowly changing flow.

Pressure Transients in a Model Gas-Blast Circuit Breaker Operating at Extra High Current Levels

Test results for model circuit breakers operating at high current levels and with large diameter nozzles show evidence of pronounced pressure transients although the circuit breaker nozzle is not severely blocked. The magnitude and duration of these transients are sufficient to affect the arc properties and hence influence arc control during the peak current phase and to influence arc extinction at current zero. However, despite their inherent importance there exists only limited information concerning such pressure variations. The purpose of this contribution is to identify the nature and sources of the transients, to establish typical thresholds for the onset of the transients, and to determine the influence of different operating conditions upon the transients. Measurements of pressure and thermal mantle variations are used in conjunction with an electrical analog model of the aerodynamic test facility to show that the pressure transients arise not only from arc generated flow impedance effects but also aerodynamic resonances. The resonant pressure transients are shown to be pronounced during the high current phase even below the thermal blocking threshold. Above the threshold, excitation of negative increment resonance following current peak produces depressed pressures during the current-zero period which may lead to a deterioration in circuit breaker performance. Higher frequency resonances also occur and become more pronounced with electrode wear. Activation of such resonances is symptomatic of axisymmetric arc instabilities which also may cause a deterioration in performance.

Data Acquisition and Processing in a Large Aerodynamic Test Center

Today, a data acquisition and processing system in a large aerodynamic test center must fulfil a number of functions, which are enumerated and analyzed here. These functions, along with the expected performance and the particular location of the test center under consideration, dictate the configurations of the best systems and the choice of hardware and software. As an example, the system utilized in the Modane and Le Fauga Centers of ONERA is described. It concerns two continuous and one intermittent wind tunnels at Modane and one low- speed pressurized wind tunnel at Le Fauga, about 600 km distant from Modane. The detailed description of the data acquisition and processing systems of these two centers is presented and discussed. OR the past quarter century, aerodynamic testing facilities have greatly contributed to the advance of the aerospace sciences and techniques. During the same period of time these facilities, which are quite often concentrated in large specialized centers, have evolved as a function of both the test requirements and the new potentials offered by scientific and technical advances. Progress in physics, and particularly in electronics and computers, has greatly in- fluenced the nature and the performance of the data acquisition and computation systems used in such centers. In France, the Office National d'Etudes et de Recherches Aerospatiales, ONERA (National Institute for Aerospace Research) operates several wind tunnels in its two large Aerodynamic Test Centers (Modane and Le Fauga), where new data acquisition and processing equipment will be utilized shortly.The design and implementation of such a costly system has been the result of two simultaneous occurrences: on the one hand the Modane center, with its very large (8-m- diam) sonic SI wind tunnel, operational for over twenty years, its supersonic continuous tunnel S2, its supersonic blowdown tunnel S3, its hypersonic tunnel S4, and its various other facilities, had to have its data acquisition and processing system renewed according to the new concepts; and on the other hand a new center was being built at Le Fauga, in the Toulouse region, some 600 km away from both Modane and Chatillon, the ONERA headquarters, with the construction of a large pressurized subsonic wind tunnel, called Fl. It was felt that this situation offered a unique opportunity to devise a coherent system that should, with possible minor ad- justments, serve efficiently for a number of years. The paper describes this new equipment and shows the successive steps followed for selecting such a new system, without entering into the detail of the various solutions retained for the wind tunnels themselves.

A Theoretical and Experimental Study of the Exhaust Noise Environment of a Proposed High Reynolds Number Tunnel

The growing interest in noise pollution has presented designers of modern aerodynamic test facilities with new problems and interesting and complex challenges. Due to the sheer magnitude of their power output, many existing aerodynamic facilities and some of those designed for the future are enormous sources of sound. As part of a feasibility and preliminary design study of a High Reynolds Number Tunnel (HIRT) currently being performed by ARO, Inc., at the Arnold Engineering Development Center (AEDC), an investigation has been conducted to (a) predict the acoustic environments which may be anticipated from the operation of HIRT and (b) perform a comprehensive experimental study using a scale-model facility in order to obtain acoustic data over the anticipated range of operational variables for HIRT. One important feature of the facility which necessitated this study is the open-circuit blowdown design which causes the starting shock wave and high-speed jet flow to exhaust into the atmosphere. A comprehensive analysis of the noise-generating mechanisms associated with the facility has been conducted, although based in some cases on engineering approximations and acoustic models of the flow environment. These data were used to define those design features of the facility which would produce predominant noise source mechanisms. Based on the analytical findings, a one-thirteenth-scale model of HIRT was designed using precise scaling of the important features of HIRT to retain, within practical limits, those design features which contribute to the noise characteristics of the facility. Utilizing the model facility, acoustic tests were performed over a broad range of operational variables representative of the operational range of the full-scale facility. Free-field acoustic measurements were taken along various polar rays around the exhaust stack of the facility to define the noise levels and spectra, directivity patterns, and propagational characteristics. Comparisons are made between the acoustic predictions and the experimental measurements and show the applicability of current noise prediction methods (which are based on jet and rocket exhaust flow) to noise problems associated with aerodynamic test facilities.

Aerodynamics at NPL, 1917–1970

The removal of the low density wind tunnel from the National Physical Laboratory (NPL) to the Royal Aircraft Establishment in December 1971 constituted the first step in the movement of several important aerodynamic test facilities, and provides an opportunity for Dr R. C. Pankhurst, Superintendent of the NPL Aerodynamics Division from 1964 to 1970, to recall briefly some of the contributions made by the division to the advancement of its subject.