Separate Wind Tunnel Research Articles

외장분리 풍동시험 기법의 전산유체해석 적용

본 논문은 외장 분리 풍동시험 기법을 적용한 전산유체해석을 통하여 획득한 데이터와 풍동시험을 통하여 획득한 데이터를 비교 연구한 것이다. 전산유체해석은 하모닉 방정식을 적용한 비정상 해석 기법을 사용하여 수행하였으며, 비정상 해석으로부터 외장의 공력계수들과 6 자유도 외장 분리 시뮬레이션을 위한 공력 데이터베이스를 생성하였다. 해당 데이터베이스와 풍동시험 기반 데이터베이스를 이용한 외장의 분리 궤적 시뮬레이션 수행하였으며, 그 결과를 비행시험 결과와 비교하였다. 비교를 통하여 시뮬레이션의 적절성을 확인하였으며, 외장 분리 풍동시험 기법을 전산유체해석에 적용하여 획득한 외장 분리 공력 데이터베이스는 외장분리 궤적 시뮬레이션 적용에 타당함을 확인하였다.

Multi-point line focused laser differential interferometer for high-speed flow fluctuation measurements.

A multi-point focused laser differential interferometer (FLDI) has been developed to measure density fluctuations at 16 points along a line. A pair of cylindrical lenses on the transmitter side of a conventional single-point FLDI instrument form two closely spaced (≤200µm), orthogonally polarized, parallel laser lines at the instrument's focus. On the receiver side of the instrument, the interference of the beams on a 16-element photodiode array results in a single line of measurements. The further addition of a Nomarski prism creates two separate measurement lines, and the addition of a second photodiode array to the instrument enables simultaneous measurements of density fluctuations along the two lines separated by several millimeters. These two lines of measurement can be conveniently oriented at any azimuthal angle relative to the instrument's optical axis on the measurement plane, coinciding with the instrument's focus. Two experiments were performed to demonstrate the capabilities of the instrument. In the first experiment, a laser-induced breakdown spark generated a traveling spherical shock wave, and measurements of the resulting density disturbance and wave velocity were obtained. These results were compared to high-speed schlieren images of the shock wave acquired at 400 kHz. In the second experiment, the multi-point FLDI instrument was used to measure density disturbances in the boundary layer of a flat plate in a Mach 6 freestream flow. The measurements were made along two lines, both approximately 6 mm in length, extending from the surface of the plate through the boundary layer. High-speed schlieren images were acquired at 100 kHz during separate wind tunnel runs at matching unit Reynolds numbers to visualize the unsteady boundary layer flow and compare to the FLDI measurements.

Hybrid pressure integration and buffeting analysis for multi-row wind loading in an array of single-axis trackers

Unrestrained single-axis solar trackers are uniquely flexible structures that can withstand more deflections than typical aeroelastic structures such as long-span bridges or aircraft wings. These distinctive features and the aerodynamics of multi-row arrays lead to the requirement of novel techniques for design wind loads. The present study presents a hybrid technique using two separate wind tunnel tests: (i) a pressure model at a relatively small scale, and (ii) a sectional model at a larger scale. The pressure model test is used to measure the buffeting forces acting on each row of the array and the sectional model study is used to extract the variation in aerodynamic stiffness and damping as a function of wind speed. The results of these separate studies are combined to numerically simulate the buffeting response of the tracker, which predicts significant inertial and self-excited forces. Comparisons between the proposed hybrid method and wind loads estimated using a dynamic amplification approach are performed. It is shown that at high wind speeds, the self-excited forces become significant and the peak design moments exceed those predicted using pressure data alone. The proposed methodology is expected to complement aeroelastic modeling as a convenient and efficient design tool.

An algorithm to separate wind tunnel background noise from turbulent boundary layer excitation

Wall pressure fluctuations generated by Turbulent Boundary Layers (TBL) provide a significant contribution in reducing the structural vibration and the aircraft cabin noise. However, it is difficult to evaluate these fluctuations accurately through a wind tunnel test because of the pollution caused by the background noise generated by the jet or the valve of the wind tunnel. In this study, a new technology named Subsection Approaching Method (SAM) is proposed to separate the wall pressure fluctuations from the background noise induced by the jet or the valve for a transonic wind tunnel test. The SAM demonstrates good performance on separating the background noise from the total pressure compared to the other method in this study. The investigation considers the effects of the sound intensity and the decay factor on the sound-source separation. The results show that the SAM can derive wall pressure fluctuations effectively even when the level of background noise is considerably higher than the level of the wall pressure fluctuations caused by the TBL. In addition, the computational precision is also analyzed based on the broad band noise tested in the wind tunnel. Two methods to improve the precision of the computation with the SAM are also suggested: decreasing the loop gain and increasing the sensors for the signal analysis.

A three degree of freedom manipulator used for store separation wind tunnel test

A three degree of freedom manipulator is presented, which is used for store separation wind tunnel test. It is a kind of mechatronics product, have small volume and large moment of torque. The paper researched the design principle of wind tunnel test equipment, also introduced the transmission principle design, physical design, control system design, drive element selection calculation and verification, dynamics computation and static structural computation of the manipulator. To satisfy the design principle of wind tunnel test equipment, some optimization design are made include optimizes the structure of drive element and cable, fairing configuration, overall dimension so that to make the device more suitable for the wind tunnel test. Some tests are made to verify the parameters of the manipulator. The results show that the device improves the load from 100 Nm to 250 Nm, control accuracy from 0.1°to 0.05°in pitch and yaw, also improves load from 10 Nm to 20 Nm, control accuracy from 0.1°to 0.05°in roll.

CFD MODELLING TO STUDY THE EFFECTS OF TABLE GRAPE PACKAGING AND STACKING ON FRUIT COOLING AND MOISTURE LOSS

Optimal packaging and storage are critical technologies in maintaining postharvest quality of fresh produce. Computational fluid dynamics (CFD) modelling was used to investigate the airflow, heat and mass transfer characteristics of packed table grapes during postharvest cooling and handling. The 3-D CFD model was applied to study the effects of packaging components and box stacking on the airflow, heat and mass transfer characteristics. The carton box was explicitly modeled, and the grape bunches inside the carry bags was treated as a porous media. The plastic liner was modeled as porous jump. The porous media and porous jump loss coefficients were determined using separate wind tunnel experiments, respectively. The presence of plastic liner increased the cooling time of grapes significantly, and the lowest moisture loss occurred in fruits packed inside a non-perforated plastic liner. However, packaging with a non-perforated plastic liner resulted in the highest in-package condensate. The airflow and the heat transfer characteristics were also highly influenced by the orientation and stacking pattern of packages. Forcing the cooling air through the package side-walls with the highest vent area resulted in better air penetration and increased produce cooling rate in the stack.

On-road and wind-tunnel measurement of motorcycle helmet noise

The noise source mechanisms involved in motorcycling include various aerodynamic sources and engine noise. The problem of noise source identification requires extensive data acquisition of a type and level that have not previously been applied. Data acquisition on track and on road are problematic due to rider safety constraints and the portability of appropriate instrumentation. One way to address this problem is the use of data from wind tunnel tests. The validity of these measurements for noise source identification must first be demonstrated. In order to achieve this extensive wind tunnel tests have been conducted and compared with the results from on-track measurements. Sound pressure levels as a function of speed were compared between on track and wind tunnel tests and were found to be comparable. Spectral conditioning techniques were applied to separate engine and wind tunnel noise from aerodynamic noise and showed that the aerodynamic components were equivalent in both cases. The spectral conditioning of on-track data showed that the contribution of engine noise to the overall noise is a function of speed and is more significant than had previously been thought. These procedures form a basis for accurate experimental measurements of motorcycle noise.

Reduction of Aerodynamic Noise from High-speed Pantograph using Porous Materials

Aerodynamic noise is a major source of wayside noise generated by high-speed railway vehicles, and thus it is important to reduce this phenomenon. For this purpose, a new aerodynamic noise reduction method that involves covering the surface of objects with particular porous materials has been developed. To verify its aerodynamic noise reduction effects, wind tunnel tests using cylinders and high-speed pantographs were conducted. Field tests using the high-speed pantograph were also conducted. The results indicated that aerodynamic noise generated from the cylinders and the high-speed pantographs was reduced by the application of porous materials, thus confirming the effectiveness of this method. An advantage of this method is that it is possible to reduce aerodynamic noise with little modification of object shape. Furthermore, separate wind tunnel tests also demonstrated the effectiveness of the method in reducing aerodynamic noise in combination with simplifying the shape to allow easier material processing.

A unified approach to aerodynamic damping and drag/lift instabilities, and its application to dry inclined cable galloping

Inclined cables of cable-stayed bridges often experience large amplitude vibrations. One of the potential excitation mechanisms is dry inclined cable galloping, which has been observed in wind tunnel tests but which has not previously been fully explained theoretically. In this paper, a general expression is derived for the quasi-steady aerodynamic damping (positive or negative) of a cylinder of arbitrary cross-section yawed/inclined to the flow, for small amplitude vibrations in any plane. The expression covers the special cases of conventional quasi-steady aerodynamic damping, Den Hartog galloping and the drag crisis, as well as dry inclined cable galloping. A nondimensional aerodynamic damping parameter governing this behaviour is proposed, which is a function of only the Reynolds number, the angle between the wind velocity and the cable axis, and the orientation of the vibration plane. Measured static force coefficients from wind tunnel tests have been used with the theoretical expression to predict values of this parameter. Two main areas of instability (i.e. negative aerodynamic damping) have been identified, both in the critical Reynolds number region, one of which was previously observed in separate wind tunnel tests on a dynamic cable model. The minimum values of structural damping required to prevent dry inclined cable galloping are defined, and other factors in the behaviour in practice are discussed.

Hyper-X Stage Separation Wind-Tunnel Test Program

NASA's Hyper-X research program was developed primarily to flight demonstrate a supersonic combustion ramjet engine, fully integrated with a forebody designed to tailor inlet flow conditions and a free expansion nozzle/afterbody to produce positive thrust at design flight conditions. With a point-designed propulsion system the vehicle must depend on some other means for boost to its design flight condition. Clean separation from this initial propulsion system stage within less than a second is critical to the success of the flight. This paper discusses the early planning activity, background, and chronology that developed the series of wind-tunnel tests to support multi-degree-of-freedom simulation of the separation process. Representative results from each series of tests are presented, and issues and concerns during the process and current status are highlighted.

Aeolian behavior of dust in a simulated Martian environment

The behavior of aeolian dust, particles 1–2 microns (μm) in diameter, was analyzed in a simulated Martian environment. Three main areas have been investigated: (1) characterizing spectral and aeolian properties of Martian particles and natural wind‐blown terrestrial dust in order to identify a suitable surrogate Martian dust, (2) emplacement of the material in the simulated Martian environment, and (3) experimental procedures and testing in the Martian Surface Wind Tunnel (MARSWIT). The first phase of the study involved choosing a terrestrial dust that closely resembled Martian dust. Data accumulated from various sources suggest that Martian dust is derived from the weathering of basaltic parent material, nontronite clay being a good candidate composition. A commercial clay, Carbondale Red Clay (CRC), was determined to be an appropriate surrogate Martian dust. Using a compressed air‐dust ejection system, an air‐entrained dust cloud was generated which settled to cover the test section in the MARSWIT. This method best replicated the natural aerodynamic settling process presumed to exist on Mars. Low‐pressure experiments were performed in the MARSWIT facility located at the NASA Ames Research Center, Moffett Field, California. Two separate wind tunnel floors were used for these experiments; one provided an aerodynamically smooth‐surface flow, and the other was an aerodynamically rough‐surface flow. Initial and momentary particle movement was recorded at friction velocities as low as 2 m/s. However, the “dust” never reached fluid saltation threshold because individual particles less than 10 μm typically do not saltate, but pass into suspension. An estimated dust flux of 3.7×10−7 g/cm2 s was determined for a friction velocity of 2 m/s. This flux could suspend about 10,000 metric tons of dust per second over the surface of Mars. The dust behavior on the smooth surface was markedly different than on the rough surface under Martian conditions. Application of the processes described above to the Martian environment suggests that on rocky surfaces dust suspension would first occur, whereas smooth plains would require higher wind speeds for dust entrainment.

Measurements of the upstream turbulent flow during wind tunnel simulations of agricultural field burning

Mean streamwise and vertical velocities as well as streamwise and vertical turbulence intensities were measured in a combustion wind tunnel used to collect pollutant emission data for agricultural field burning. Objectives were to compare the flow field upstream of a fire to that without a fire present and to compare the wind tunnel flow upstream of a fire to field conditions. Vertical centerline traverses with an anemometer were conducted for 32 separate wind tunnel operating configurations (wind speed, position in the tunnel, with or without fire, ceiling position, and floor condition) with one replication for each configuration (total of 64 traverses). Certain configurational changes in the wind tunnel had substantial effects on the flow field. Turbulence intensities and velocity profiles (as modeled by the log law-of-the-wall to determinez0 andu* values) in the wind tunnel were comparable to those in the field as reported in the literature. Velocities and turbulence intensities were generally higher, however, with a fire present in the tunnel and all other conditions constant.

Recent improvements in prediction techniques for supersonic weapon separation

The influence function method (IFM) has demonstrated a unique capability for accurately predicting store aerodynamic characteristics in an aircraft flowfield. To apply this method, one must know the force and moment influence functions of the respective stores involved. These are obtained from a separate wind tunnel test where the forces and moments on the subject store are measured as the store is traversed through an oblique shock generated by a wedge or inclined plate. It was recently determined that these calibration forces and moments could be accurately predicted by the PANAIR pilot code, thus opening up the possibility for determining the required influence functions theoretically. This suggests that, in many instances, further economies in weapon separation testing are possible by using theoretically determined weapon In addition, a procedure has been developed which combines PANAIR predictions of the parent aircraft flowfield with PANAIR store calibrations. This process enables the calculation of supersonic store behavior without the need of any a priori experimental data, at a considerable cost savings compared to using the PANAIR pilot code to calculate the store forces and moments at every point in the traverse.

Unsteady environments and responses of the Shuttle combined loads Orbiter test

Separate and combined wind tunnel and vibration shaker tests were conducted on two structural panels representative of the Shuttle Orbiter in the NASA/LaRC 8 ft Transonic Pressure Tunnel to determine the effects of combined loads on the Thermal Protection System (TPS). Objectives of this test were to provide a combined full scale load environment and realistic time history of the dynamic pressures and responses and Mach numbers (through transonic) to these panels. Panels were selected from locations where interactive load sources such as aerodynamic shock waves, turbulent boundary layers, strut-induced vorticity, and substrate deformation combined to provide high bonding loads between the TPS and the Orbiter structure. Test panels were instrumented with static and dynamic pressure gauges, accelerometers, deflectometers, strain gauges, schlieren and high speed photography, and instrumentation necessary to determine SIP/structure interface loads. Two test specimens of each Orbiter panel were utilized. The first panel for each test was utilized to calibrate the tunnel and shaker system and gather data for applied static and dynamic loads. The second panel or each test was subjected to flight time exposures only so that TPS characteristics as a function flight mission exposure could be determined.