Dual hologram shearing interference technique with enhanced sensitivity for wind tunnel testing

The effectiveness of the instrumentation, techniques, and wind tunnel flow characterizations in the U.S. large scale wind tunnels for accuracy in making increasingly finer drag measurements on airfoils is assessed. The more reliable measurement is necessary due to refined designs of airfoils and the need to continue to improve the economic performance of commercial aircraft. Consequently, the effects of flows in wind tunnels, compared with those in the freestream environment, have become a critical factor. Dynamic flow properties in individual wind tunnels have to be documented in order to assure reproducible results. Laser velocimetry is a suitable tool for nonintrusive measurement of the mean velocity, turbulence intensity, and the shear stress in wind tunnel flowfields. It is suggested that future wind tunnel studies be designed to remain within the diagnostic capabilities available at the site.

A video image analysis system for concentration measurements and flow visualization in building wakes

The historical development of laser velocimetry and its application to low-speed (less than 100 m/sec) aerodynamic flows in the subsonic wind tunnels at Ames Research Center is reviewed. A fully three dimensional velocimeter for the Ames 7- by 10-Foot Wind Tunnel is described, and its capabilities are presented through sample data from a recent experiment. Finally, a long-range (2.6 to 10 m) velocimeter that is designed to be installed within the test section of the Ames 40- by 80-Foot Wind Tunnel is described and sample data are presented.

Wind tunnel measurement quality in testing of a standard model

Numerical predictions of the longitudinal aerodynamic characteristics for the Ares I class of vehicles, along with the associated error estimate derived from an iterative convergence grid refinement, are presented. Computational results are based on the unstructured grid, Reynolds-averaged Navier-Stokes flow solver USM3D, with an assumption that the flow is fully turbulent over the entire vehicle. This effort was designed to complement the prior computational activities conducted over the past five years in support of the Ares I Project with the emphasis on the vehicle s last design cycle designated as the A106 configuration. Due to a lack of flight data for this particular design s outer mold line, the initial vehicle s aerodynamic predictions and the associated error estimates were first assessed and validated against the available experimental data at representative wind tunnel flow conditions pertinent to the ascent phase of the trajectory without including any propulsion effects. Subsequently, the established procedures were then applied to obtain the longitudinal aerodynamic predictions at the selected flight flow conditions. Sample computed results and the correlations with the experimental measurements are presented. In addition, the present analysis includes the relevant data to highlight the balance between the prediction accuracy against the grid size and, thus, the corresponding computer resource requirements for the computations at both wind tunnel and flight flow conditions. NOTE: Some details have been removed from selected plots and figures in compliance with the sensitive but unclassified (SBU) restrictions. However, the content still conveys the merits of the technical approach and the relevant results.

Results of wave loading experiments on chord sections and isolated bays of two typical jack-up leg designs are discussed. The tests were carried out at a large scale (approx. 1:2 for chords and approx. 1:4 for bays) in regular and random waves with large wave heights (up to 2.4 metres). This large scale is necessary to obtain flow conditions which are representative for full scale offshore conditions. INTRODUCTION Wave induced forces are a major contribution to the overall loading on a jack-up platform. They play an important role in the design of a jack-up platform or in the analysis of existing jack-ups, when their fitness for use at a specific site is considered. While a large amount of experimental data has been gathered on smooth and rough circular cylinders in planar oscillatory flow and in waves, very little information is available fromtests with jack-up legs in such conditions. Itis generally assumed in the jack-up industry that the wave loading on jack-up platforms canbe based on experimental data obtained in stationary flow in wind tunnels. In view of the application of such platforms in deeper water and more severe environmental conditions, this situation is not satisfactory. Therefore, a joint industry project was carried out to improve knowledge and understanding of the wave loading on jack-up legs. The basic objectives of this project were:to determine wave forces on typical jack-up legs under representative wave conditions and with the smallest possible scale effects andto achieve results for engineering applications which have a more general bearing than on the tested legs only. This paper describes some results of wave loading experiments on elements (chords and isolated bays) of jack-up legs, carried out within the scope of this joint industry project. In view of the second objective, smaller elements (chords) were tested beside larger elements (bays) to enable determination of interaction coefficients. Bracings were not tested separately in this programme, because a large amount of literature is already available on circular members in stationary and oscillating flow. For the extrapolation of the laboratory data to full scale offshore conditions, it is essential to obtain these data in post-criticalflow conditions. To achieve the required Reynolds- numbers, the tests were therefore carriedout at a large scale (approx. 1:2 for the chords and approx. 1:4 for the bays) in regular and irregular waves with large wave heights (maximum wave height in irregular wave trains up to 2.4 metres). This paper concentrates on the execution and the results of the wave loading experiments. In future publications, attention will be focused on the composition of elementary results to bay and leg results and the comparison of the composed results with measured results to check on interactions.

Turbulence Model and Validation of Air Flow in Wind Tunnel

As an initial analysis, numerical simulation has more advantages in saving time and costs regarding experiments. For example, variations in flow conditions and geometry can be adjusted easily to obtain results. Computational fluid dynamics (CFD) methods, such as the k-? model, renormalization group (RNG) k-? model and reynolds stress model (RSM), are widely used to conduct research on different objects and conditions. Choosing the appropriate model helps produce and develop constant values. Modeling studies as appropriate, i.e., in the turbulent flow simulation in the wind tunnel, is done to get a more accurate result. This study was conducted by comparing the results of the simulation k-? model, RNG k-? model and RSM, which is validated by the test results. The air had a density of 1,205 kg/m3, a viscosity of 4×10-5 m2/s and a normal speed of 6 m/s. By comparing the simulation results of the k-? model, RNG k-? model and RSM, which is validated by the test results, the third turbulence model provided good results to predict the distribution of speed and pressure of the fluid flow in the wind tunnel. As for predicting the turbulent kinetic energy, turbulent dissipation rate and turbulent effective viscosity, the k-? model was effectively used with comparable results to the RSM models.

Holography has been used to record high speed events for the past 20 years. The events include particle and projective impacts, particle dispersion, and a variety of flow field configurations of interest in aerodynamics. Most of these studies and the ones discussed in this article, use either ruby lasers or neodymium YAG lasers, with pulse durations of 10 to 20 nanoseconds. Holography is important for particle dispersion studies because the particle locations, shapes and velocities can be examined three dimensionally after the event has passed. Examples occur in the examination of fuel spray jets and liquid droplet breakup. Holography is ideal for the study of flows in wind tunnels because of its ability to capture the phase of the coherent light transmitted through these fields. Several rather elaborate holographic interferometer methods have been implemented including double pulse, finite fringe, and phase cancellation. Two recent and ongoing programs which also use hologram interferometry are of special interest. The first of these is a study of the imaging capabilities through the turbulent boundary layers which exist over optical windows in high speed aircraft. Recent findings show that some corrections for this turbulence are possible. The second program deals with the analysis of the three dimensional flow field about a rotating helicopter blade. It is interesting because it combines holographic flow field analysis with computed tomography.

What is the effect of self-induced pressure waves and their wall reflections on low Reynolds number airfoil flow in wind tunnels?

This paper deals with design and analysis of intermittent supersonic wind tunnels. System can be constructed by allowing air at atmospheric pressure to pass through a converging-diverging nozzle, a test section and a diffuser into a vacuum tank. The governing equations of compressible fluid flow have been solved numerically using flux vector splitting method to obtain running time under which it works at the design Mach number. The formulation has been tested on the theory of quasi one-dimensional compressible flow. The numerical results are in good agreement with the results of the theory.

The objective of this work is the study of atmospheric pollutants dispersion problems in wind tunnels. The use of a reduced scale model provides the ability to analyze the process of dispersion in complex models. It also allows the study of different situations and alternatives in the source design. The wind tunnel pollutants dispersion simulation requires two sets of similarity criteria; the first established that the wind tunnel flow must be similar to natural wind in the atmospheric boundary layer, and the second, that the model source characteristics must be similar to prototype. In this work, the similarity criteria of the atmospheric flow and the emission source are studied to reproduce dispersion processes and develop a first approach to the experimental study of this phenomenon. Firstly, the results of a visualization dispersion process test performed at the wind tunnel of the Facultad de Ingenieria de la Universidad Nacional del Nordeste, using smoke as a tracer and considering three operation velocities are presented. The study of the plume evolution was made by image digital processing and the plume rise is also discussed by comparison of measurements with theoretical values. Finally, preliminary experiments results are presented to evaluate concentration field from an isolated point emission source using a light gas and reduced scale model. Keywords: atmospheric dispersion, similarity, wind tunnel.

The flow in a virtual wind tunnel with a geometry corresponding to the actual IT-302M hot-shot wind tunnel was considered. CFD simulations were made for the initial conditions taken from the experiment. The process of gas throttling between the first and second prechambers, the heat exchange of the gas with the wall, and the process of the wind tunnel start were studied in a nonstationary approach. The comparison is made with the experimental flow parameters measured in the first and second prechambers as well as with PIV velocity measurements at the nozzle exit. It is shown that the calculated results obtained have good convergence with the experimental data; the flow model from a closed volume through a porous insert simulates the start-up process of the IT-302M installation with good accuracy; the boundary condition in the form of a constant temperature makes it possible to obtain data close to the results of solving the conjugate heat transfer problem.

A method for reducing the flow-induced self-noise of acoustic array microphones was demonstrated in a wind tunnel. Unsteady boundary-layer flow in the wind tunnel induces large pressure fluctuations on exposed, flushmounted microphone diaphragms, reducing the signal-tonoise capability of microphone arrays. Two important steps were taken to reduce this background noise. First, the microphones were recessed to separate the microphones from the unsteady flow. Second, a porous surface material was placed above the microphones to act as an aerodynamic surface while allowing acoustic signals to pass through to the microphones. Previous attempts at this approach used perforated plates as the surface material, which tended to fatigue in the unsteady flow. The increased acoustic impedance of thicker materials caused reverberation between the surface and the microphone mounting plate. This latest attempt used a stretched sheet of Kevlar ® as the surface. The extreme strength and durability of the Kevlar ® withstood flow-induced fatigue while providing very low acoustic impedance with little attenuation of sound for most frequencies. Data is presented for two wind tunnel tests that demonstrate the capabilities of the recessed Kevlar ® array.

<div class="htmlview paragraph">This paper is the first of two papers that address the simulation and effects of turbulence on surface vehicle aerodynamics. This, the first paper, focuses on the characteristics of the turbulent flow field encountered by a road vehicle. The natural wind environment is usually unsteady but is almost universally replaced by a smooth flow in both wind tunnel and computational domains. In this paper, the characteristics of turbulence in the relative-velocity co-ordinate system of a moving ground vehicle are reviewed, drawing on work from Wind Engineering experience. Data are provided on typical turbulence levels, probability density functions and velocity spectra to which vehicles are exposed. The focus is on atmospheric turbulence, however the transient flow field from the wakes of other road vehicles and roadside objects are also considered. The effects of turbulence on vehicle aerodynamics and methods of experimental simulation are reviewed in a companion paper, Part 2 (<span class="xref">Watkins and Cooper, 2007</span>).</div>