High Reynolds Number Testing Research Articles

Skin-Friction-Based Identification of the Critical Lines in a Transonic, High Reynolds Number Flow via Temperature-Sensitive Paint.

In this contribution, three methodologies based on temperature-sensitive paint (TSP) data were further developed and applied for the optical determination of the critical locations of flow separation and reattachment in compressible, high Reynolds number flows. The methodologies rely on skin-friction extraction approaches developed for low-speed flows, which were adapted in this work to study flow separation and reattachment in the presence of shock-wave/boundary-layer interaction. In a first approach, skin-friction topological maps were obtained from time-averaged surface temperature distributions, thus enabling the identification of the critical lines as converging and diverging skin-friction lines. In the other two approaches, the critical lines were identified from the maps of the propagation celerity of temperature perturbations, which were determined from time-resolved TSP data. The experiments were conducted at a freestream Mach number of 0.72 and a chord Reynolds number of 9.7 million in the Transonic Wind Tunnel Göttingen on a VA-2 supercritical airfoil model, which was equipped with two exchangeable TSP modules specifically designed for transonic, high Reynolds number tests. The separation and reattachment lines identified via the three different TSP-based approaches were shown to be in mutual agreement, and were also found to be in agreement with reference experimental and numerical data.

Numerical investigation of nitrogen condensation flow over airfoil in cryogenic wind tunnel

Cryogenic wind tunnel is an equipment for the requirement of high Reynolds number test of the aircraft via the method of reducing the test temperature. However, the test validity is extremely possible to be destroyed by the occurrence of condensation in cryogenic environment. To understand the characteristics of condensation flow over the airfoil, a two-phase flow was developed with the help of ANSYS Fluent. For 0.137-m NACA 0012-64 airfoil, numerical simulations of 32 cases under three different Reynolds numbers (~26 × 106, ~38 × 106 and ~44 × 106) were implemented. The simulated results show that only when the temperature of local gas-flow crosses the saturation line and is lower than a critical point there is enough condensate to alter some flow properties noticeably, such as pressure, temperature and Mach number. The achievement of maximum local supercooled degree decreases with the increase in operating total pressure. For a given test Reynolds number, when the static pressure and temperature of the gas is on the lower temperature side of the saturation curve, a reduction of operating pressure and temperature among a reasonable range is also believed to not cause the condensation effect on the aerodynamic test. On the bright side, lower operating pressure will provide the advantages of less liquid nitrogen injection and less drive power of fan. From another point of view, under the premise of ensuring that the gas-flow local temperature is higher than that at Wilson point, the reduction in the operating temperature as much as possible can greatly increase the test Reynolds number. The built two-phase model supplies an approach for investigating the condensation effect on airfoil test in cryogenic wind tunnel, and resulting findings guide the determination of working conditions for airfoil Reynolds number test.

A double-multiple streamtube model for vertical axis wind turbines of arbitrary rotor loading

Abstract. We introduce an improved formulation of the double-multiple streamtube (DMST) model for the prediction of the flow quantities of vertical axis wind turbines (VAWT). The improvement of the new formulation lies in that it renders the DMST valid for any induction factor, i.e., for any combination of rotor solidity and tip speed ratio. This is done by replacing the Rankine–Froude momentum theory of the DMST, which is invalid for moderate and high induction factors, with a new momentum theory recently proposed, which provides sensible results for any induction factor. The predictions of the two DMST formulations are compared with VAWT power measurements obtained at Princeton's High Reynolds number Test Facility, over a range of tip speed ratios, rotor solidities, and Reynolds numbers, including those experienced by full-scale turbines. The results show that the new DMST formulation demonstrates a better overall performance, compared to the conventional one, when the rotor loading is moderate or high.

Additional Comparison of Iced Aerodynamic Measurements on a Swept Wing from Two Wind Tunnels

<div class="section abstract"><div class="htmlview paragraph">Artificial ice shapes of various geometric fidelity were tested on a wing model based on the Common Research Model. Low Reynolds number tests were conducted at Wichita State University’s Walter H. Beech Memorial Wind Tunnel utilizing an 8.9% scale model, and high Reynolds number tests were conducted at ONERA’s F1 wind tunnel utilizing a 13.3% scale model. Several identical geometrically-scaled ice shapes were tested at both facilities, and the results were compared at overlapping Reynolds and Mach numbers. This was to ensure that the results and trends observed at low Reynolds number could be applied and continued to high, near-flight Reynolds number. The data from Wichita State University and ONERA F1 agreed well at matched Reynolds and Mach numbers. The lift and pitching moment curves agreed very well for most configurations. This confirmed results from previous tests with other ice shapes that indicated the data from the low Reynolds number tests could be used to understand iced-swept-wing aerodynamics at high Reynolds number. This allows ice aerodynamics testing to be performed at low Reynolds number facilities with much lower operating costs and generate results that are applicable to flight Reynolds number.</div></div>

Vertical-axis wind turbine experiments at full dynamic similarity

Laboratory experiments were performed on a geometrically scaled vertical-axis wind turbine model over an unprecedented range of Reynolds numbers, including and exceeding those of the full-scale turbine. The study was performed in the high-pressure environment of the Princeton High Reynolds number Test Facility (HRTF). Utilizing highly compressed air as the working fluid enabled extremely high Reynolds numbers while still maintaining dynamic similarity by matching the tip speed ratio (defined as the ratio of tip velocity to free stream, $\unicode[STIX]{x1D706}=\unicode[STIX]{x1D714}R/U$) and Mach number (defined at the turbine tip, $Ma=\unicode[STIX]{x1D714}R/a$). Preliminary comparisons are made with measurements from the full-scale field turbine. Peak power for both the field data and experiments resides around $\unicode[STIX]{x1D706}=1$. In addition, a systematic investigation of trends with Reynolds number was performed in the laboratory, which revealed details about the asymptotic behaviour. It was shown that the parameter that characterizes invariance in the power coefficient was the Reynolds number based on blade chord conditions ($Re_{c}$). The power coefficient reaches its asymptotic value when $Re_{c}>1.5\times 10^{6}$, which is higher than what the field turbine experiences. The asymptotic power curve is found, which is invariant to further increases in Reynolds number.

High Reynolds Number Test Examples in ATLA Trisonic Wind Tunnel

High Reynolds Number Test Examples in ATLA Trisonic Wind Tunnel

High Reynolds Number Test in Development of Ministry of Defense Large Aircraft

High Reynolds Number Test in Development of Ministry of Defense Large Aircraft

Structural Design of Shanghai Tower for Wind Loads

Nearby Jin Mao tower and the World Financial Center, the 632-meter, 121-story mixed-use Shanghai tower will be the tallest super tall tower in the new Lujiazui Finance and Trade Zone of Shanghai. Due to the super tall height, curved façade and spiraling form of the Shanghai tower project, wind is the dominant lateral load and governed many aspects of the structural design. To precisely determine the design wind loads, a detailed wind climate study was conducted. The influences of typhoon events and typhoon profiles were considered in the wind climate study. Due to its long structural period, the across-wind load of the Shanghai tower project is prominent. Aerodynamic optimization studies were conducted to reduce the correlation of vortex shedding along the building height, and thus reduce the across-wind building response. The optimization results show that the across wind load can be effectively reduced with certain building configuration. Detailed wind tunnel studies, including HFFB and HFPI studies, high Reynolds number tests and aeroelastic model tests, were conducted to accurately capture the wind load on the building. The wind load parameters, such as the Shape factor, Strouhal number and the terrain type, were obtained and derived from the wind tunnel studies. The wind load and wind induced structural responses obtained from the wind tunnel studies were then compared with those calculated based on Chinese load code. The design criteria for the ultimate limit check and serviceability limit check of Shanghai tower for wind loads were discussed. Finally, the building vibration under wind load and the related human comfort problem is addressed. Different human comfort criteria are compared and the building acceleration results from both the wind tunnel tests and code-based calculation are discussed.

Tip Vortex Cavitation Inception Scaling for High Reynolds Number Applications

Tip vortices generated by marine lifting surfaces such as propeller blades, ship rudders, hydrofoil wings, and antiroll fins can lead to cavitation. Prediction of the onset of this cavitation depends on model tests at Reynolds numbers much lower than those for the corresponding full-scale flows. The effect of Reynolds number variations on the scaling of tip vortex cavitation inception is investigated using a theoretical flow similarity approach. The ratio of the circulations in the full-scale and model-scale trailing vortices is obtained by assuming that the spanwise distributions of the section lift coefficients are the same between the model-scale and the full-scale. The vortex pressure distributions and core sizes are derived using the Rankine vortex model and McCormick’s assumption about the dependence of the vortex core size on the boundary layer thickness at the tip region. Using a logarithmic law to describe the velocity profile in the boundary layer over a large range of Reynolds number, the boundary layer thickness becomes dependent on the Reynolds number to a varying power. In deriving the scaling of the cavitation inception index as the ratio of Reynolds numbers to an exponent m, the values of m are not constant and are dependent on the values of the model- and full-scale Reynolds numbers themselves. This contrasts traditional scaling for which m is treated as a fixed value that is independent of Reynolds numbers. At very high Reynolds numbers, the present theory predicts the value of m to approach zero, consistent with the trend of these flows to become inviscid. Comparison of the present theory with available experimental data shows promising results, especially with recent results from high Reynolds number tests. Numerical examples of the values of m are given for different model- to full-scale sizes and Reynolds numbers.

National Transonic Facility Model and Tunnel Vibrations

Since coming online in 1984, the National Transonic Facility (NTF) cryogenic wind tunnel at the NASA Langley Research Center has provided unique high Reynolds number testing capability. While turbulence levels in the tunnel, expressed in terms of percent dynamic pressure, are typical of other transonic wind tunnels, the significantly increased load levels utilized to achieve flight Reynolds numbers, in conjunction with the unique structural design requirements for cryogenic operation, have brought forward the issue of model and model support structure vibrations. This paper reports new experimental measurements documenting aerodynamic and structural dynamics processes involved in such vibrations experienced in the NTF. In particular, evidence of local un-steady airloads developed about the model support strut is shown and related to well documented acoustic features known as Parker modes. Two-dimensional unsteady viscous computations illustrate this model support structure loading mechanism.

Applications of dense gases to model testing for aeronautical and hydrodynamic applications

Here we review the advantages and disadvantages of using highly compressed air and other working fluids to test submarines and aircraft at full-scale Reynolds numbers. The conclusions are based on the design and implementation of two facilities at Princeton: the DARPA/ONR Superpipe apparatus built at Princeton to enable accurate pipe flow measurements over three orders of magnitude in Reynolds numbers, and the ONR High Reynolds Number Testing Facility (HRTF), designed to test submarine models at 1/5th full-scale Reynolds numbers.

Performance of a detonation driven shock tunnel

A detonation driven shock tunnel is useful as a ground test facility for hypersonic flow research. By attaching a convergent section ahead of the primary diaphragm in the driver section, the downstream operation mode became available to generate a high-enthalpy test flow. A 100 mm diameter shock tunnel was for the first time installed in the Laboratory of High-Temperature-Gas Dynamics (LHD), Institute of Mechanics, Chinese Academy of Sciences, and after its continuous refitments, a high performance detonation driven shock tunnel was achieved to generate high-enthalpy and high-Reynolds number test flows. A new method to burst a metal diaphragm with the downstream operation mode is discussed.

Advancement of Semispan Testing at the National Transonic Facility

A need for low-speed, high Reynolds number test capabilities has been identified for the design and development of advanced subsonic transport high-lift systems. In support of this need, multiple investigations have been conducted in the National Transonic Facility (NTF) at NASA Langley Research Center to develop a semispan testing capability that will provide the low-speed, flight Reynolds number data currently unattainable using conventional sting-mounted, full-span models. Although a semispan testing capability will effectively double the Reynolds number capability over full-span models, it does come at the expense of contending with the issue of the interaction of the flow over the model with the wind-tunnel wall boundary layer. To address this issue, the size and shape of the semispan model mounting geometry has been investigated, and the results are presented herein. The cryogenic operating environment of the NTF produced another semispan test technique issue in that varying thermal gradients have developed on the large semispan balance. The suspected cause of these thermal gradients and methods to eliminate them are presented

Field Calibration of Orifice Meters for Natural Gas Flow

This paper presents the orifice calibration results for nominal 15.24, 10.16, and 5.08-cm (6, 4, 2-in.) orifice meters conducted at the Chevron’s Sand Hills natural gas flow measurement facility in Crane, Texas. Over 200 test runs were collected in a field environment to study the accuracy of the orifice meters. Data were obtained at beta ratios ranging from 0.12 to 0.74 at the nominal conditions of 4576 kPa and 27°C (650 psig and 80°F) with a 0.57 specific gravity processed, pipeline quality natural gas. A bank of critical flow nozzles was used as the flow rate proving device to calibrate the orifice meters. Orifice discharge coefficients were computed with ANSI/API 2530-1985 (AGA3) and ISO 5167/ASME MFC-3M-1984 equations for every set of data points. The uncertainty of the calibration system was analyzed according to The American National Standard (ANSI/ASME MFC-2M-A1983). The 10.16 and 5.08-cm (4 and 2-in.) orifice discharge coefficients agreed with the ANSI and ISO standards within the estimated uncertainty level. However, the 15.24-cm (6-in.) meter deviated up to − 2 percent at a beta ratio of 0.74. With the orifice bore Reynolds numbers ranging from 1 to 9 million, the Sand Hills calibration data bridge the gap between the Ohio State water data at low Reynolds numbers and Chevron’s high Reynolds number test data taken at a larger test facility in Venice, Louisiana. The test results also successfully demonstrated that orifice meters can be accurately proved with critical flow nozzles under realistic field conditions.

Mach number control of Ludwieg tubes

Ludwieg tubes offer a convenient and inexpensive way to provide high Reynolds number test flows; their primary defect is the very short run time available for flow measurement. Even during this period, the test section Mach number is liable to be affected by the boundary-layer growth along charge tube walls and shows gradual increase. In order to decrease this Mach number creep, a Ludwieg tube equipped with a quick-moving choker flap is developed. Through use of the flap the effective area ratio of the test section to the sonic throat is kept essentially constant for some period during the nominal run time. An appreciable time lag is observed between the tunnel start and the establishment of the constant Mach number flow. The finite inertia of the flap and the flap drive mechanism as well as the finite pressure signal propagation speed are the main causes of the delay and several means to eliminate the lag are discussed.

Surface roughness studies for wind tunnel models used in high Reynolds number testing

This paper focuses on stylus and optical techniques for the measurement of surface roughness in wind tunnel models. The stylus instruments provide detailed information, such as surface profiles and area maps, that may then be used either to calculate statistical properties (i.e., the rms surface roughness) or to study individual surface peaks or other features. By contrast, certain optical techniques yield area-averaged statistical properties of the surface roughness directly. Two instruments that use the technique of optical angular scattering are compared. One is a research instrument that has been developed to study the basic scattering phenomena by testing the optical theories and surface models used in inverse calculations of statistical roughness parameters. The second instrument is more compact and is under development as a hand held, on-line device to be used during manufacture of wind tunnel models for the National Transonic Facility at NASA Langley Research Center. The scattering geometries for the two instruments are compared and results from these instruments and the stylus technique are shown for roughness specimens that are typical of the surface finish of wind tunnel models.

The application of cryogenics to high Reynolds number testing in wind tunnels. Part 2: Development and application of the cryogenic wind tunnel concept

An improved way to increase the Reynolds number capability of wind tunnels has been developed through the application of cryogenic technology. Part 1 of this two-part review covered the evolution, theory, and major advantages of cryogenic wind tunnels. This paper describes the development and early application of the cryogenic wind tunnel concept in the United States at the NASA Langley Research Center. Also presented are some of the major activities around the world related to cryogenic wind tunnels, the most significant of which is a large transonic cryogenic tunnel recently completed at the Langley Research Center.

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.

Wall-wake - Flow behind a leading edge obstacle

as our present one is just those truncation errors which are gradually being eliminated. These difficulties raise a crucial question, which concerns all numerical solutions of complex problems; namely, how good are the resulting numerical solutions? Where exact-analytical solutions or pertinent experimental results are on hand, the previous question can be readily answered. In our present problem we have on hand the shockless supercritical hodograph solutions calculated by Nieuwland, and will shortly have two-dimensional, high Reynolds number tests by Rainbird for the NACA 64A-410 airfoil, which will serve for comparison purposes. Although the calculation for the Nieuwland profile requires further refinement, and a high Reynolds number comparison test is yet to be obtained for the NACA 64A-410 profile, we hope that the present results will serve to demonstrate the potential of the present unsteady finite difference procedure.