Viscous interaction effects on a static pressure probe at m equals 6

We examined 11 cases when the interplanetary magnetic field (IMF) was intensely northward (> 10 nT) for long durations of time (> 3 hours), to quantitatively determine an upper limit on the efficiency of solar wind energy injection into the magnetosphere. We have specifically selected these large BN events to minimize the effects of magnetic reconnection. Many of these cases occurred during intervals of high‐speed streams associated with coronal mass ejections when viscous interaction effects might be at a maximum. It is found that the typical efficiency of solar wind energy injection into the magnetosphere is 1.0 × 10−3 to 4.0 × 10−3, 100 to 30 times less efficient than during periods of intense southward IMFs. Other energy sinks not included in these numbers are discussed. Estimates of their magnitudes are provided.

Particle coagulation in steady turbulent flows: Application to smoke aging

A shock tunnel is used to perform tests at hypersonic flow conditions including weak real gas effects. Pressure and heat flux distributions are measured around typical re-entry configurations. From these data cp values and Stanton numbers are deduced. For constant Mach and Reynolds number the experimental results achieved indicate a strong influence of the total temperature on the Stanton number distribution. For the results presented this behavior is mainly based on entropy layer and viscous interaction effects. A correlation function which takes into account these effects correlates the Stanton numbers achieved for different flow conditions and in different wind tunnels fairly well.

: An initial experimental program was previously conducted to study the problems in using static pressure probes for flow calibration purposes in low- density, hypervelocity wind tunnels with continuous flow. This data is reviewed in the light of more recent data on thermal transpiration. Results indicate that such probes may be used for what might be termed secondary calibrations, but care is required in interpreting the results. The present experiment yielded data which are compared to static pressures calculated from impact- pressure probe calibrations.

: Results are presented for chemical nonequilibrium inviscid and viscid (laminar) flow field calculations around spherically blunted cone geometries (10-, 15-, and 20-deg half-angle) at high altitude, high-speed, zero angle-of-attack conditions in the earth's atmosphere (250,000 ft at 25,000 ft/sec, 200,000 ft at 20,000 ft/sec, and 150,000 ft at 15,000 ft/sec). The effects of atom recombination at the body surface are analyzed by considering both catalytic and noncatalytic wall conditions for three different wall temperatures (540, 2500, and 5000R). Injection of a foreign gas (either nonreacting helium or argon or chemically reacting carbon dioxide) is included in order to study the effects of mass transfer. Treatment of the stagnation point using both boundary-layer and thin viscous shock-layer analyses is emphasized, as well as the influence of viscous interaction over the entire body. (Author)

Simultaneous measurement of velocity and pressure near the turbulent/non-turbulent interface of a planar turbulent jet

It is possible to encounter molten fuel pools in the course of events during a hypothetical Liquid Metal Fast Breeder Reactor accident. In such cases it may be important to estimate correctly the rate of melting of the pool walls and bottom, which are governed by the rate of heat transfer to those materials. The heat transfer characteristics of internally heated two-phase pools are thus of interest. Heat transfer measurements were made in the horizontal and downward directions both in transient and in steady state. The transient study involved slow cooling or heating of the pool liquid, while in the steady state case heat was provided by electrical immersion heaters. A permanent gas was injected from a distributed hypodermic tubing network with two hole sizes. Void fraction measurements were also made by static pressure probes. The data is reported as plots of Nusselts number versus Reynolds number and surface evaporation and entrainment effects for a boiling pool were estimated for comparison purposes.

The simultaneous measurement of the velocity and pressure in a plane jet has been performed by using a combined probe that consists of an X-type hot-wire probe and a static pressure probe. Firstly, the conditional ensemble averaged statics are investigated on the basis of the intermittency function obtained from the velocity signal by the hot-wire sensor set in the intermittent region of a plane jet. Secondly, the validity of the models for a turbulent and pressure diffusion term is investigated. The measurement results show that the cross-streamwise profile of the diffusion term in the turbulent energy transport equation differs significantly, according to the state of the flow (turbulent or non-turbulent flow) in the intermittent region. By decomposing the diffusion term into two terms, i.e., the turbulent diffusion term and the pressure diffusion term and estimating each term separately, it is found that the cross-streamwise profile of the pressure diffusion term is virtually the same, irrespective of the state of the flow in the intermittent region. This indicates that the difference in the cross-steramwise profile of the diffusion term is cause by the difference in the turbulent diffusion term. In addition, the evaluation of the two kinds of gradient diffusion models of the Reynolds stress transport equation shows that the model constants become constant and the validity of these models can be confirmed except for the region near the jet centerline and intermittent region. Finally, it is shown that both slow-part and rapid-part of the velocity-pressure correlation term must be modeled appropriately to predict the velocity-pressure correlation correctly.

: The objective of this work is to provide basic gas-dynamical information on the wakes of nozzle cusps such as employed in gas-dynamic-laser nozzle arrays. A three-nozzle array was designed, built and installed in the Aeronutronic supersonic Wind Tunnel. Test runs were made to check the overall performance of the nozzle-diffuser system at Mach 4, nozzle exit Reynolds number of 100,000 and nozzle wall temperatures down to 60% of stagnation, in continuous airflow. Diagnostics consisted of spark-schlieren photography, pitot and static pressure probes, total-temperature probes and hot film anemometers. It was found that continuos unchoked flow could be obtained with a simple diffuser, and that the flow was two-dimensional even without resorting to sidewall junction tailoring. Good qualitative and fair to good quantitative agreement was found with earlier wake predictions published under the present contract. The virtual wake origin was found to lie near the nozzle throat and the near wake nonequilibrium region occupied a length equal to two nozzle exit heights beyond the trailing edge. Without cooling the wake was laminar, with long wavelength fluctuations which merit further study. With nozzle cooling transition to turbulence in the wake advanced upstream in agreement with earlier predictions of wake stability.

An experimental study of nonequilibrium expanding flows has been carried out by measuring the static pressure at several axial locations in a 30° included angle conical nozzle attached to the reflected end of a combustion driven shock tube. In the axial survey, measurements were made at locations corresponding to geometric area ratios of from 36 to 576. Reservoir stagnation conditions were: 1000 psia, 1350°K; 450 psia, 4000°K; and 250 psia, 7000°K. The test gases used in this study were dry room air, extra-dry analyzed air, and a high-purity mixture of 80% nitrogen and 20% oxygen. The data reduction procedures that have been employed in this study are discussed. The methods for treating effects due to boundary-layer growth both on the nozzle walls and on the static-pressure probe, static-pressure probe size, flow gradients in the nozzle, etc., are outlined. It has been found that corrections for these effects are necessary to interpret properly static-pressure data. The apparent disagreement between previous experimental investigations and theoretical analyses is traceable in a large measure to these corrections. The measurements are compared with results obtained using a one-dimensional analysis that incorporates a gas kinetic model based on the best available chemical data. It is shown that the experimental data are in good agreement with the theoretical results.

Simultaneous measurement of fluctuating velocity and pressure by a static-pressure probe and a hot-wire probe was performed in the near wake of a circular cylinder, in order to strengthen reliability of the measurement technique. Effect of geometry of the static-pressure probe was systematically investigated, and validity of the measurement results was addressed by quantitative comparison with reference data by a large-eddy simulation. Interference between the probes was found to mainly depend on the diameter of the pressure probe and only weakly on the length. A certain time lag between the velocity and pressure signals was detected in the experiment, and the measurement results of velocity–pressure correlation \(\overline{up}\) and \(\overline{vp}\) obtained with the correction of the time lag were in good agreement with the computational results. It was also found that the measurement of \(\overline{vp}\) is extremely sensitive to a small time lag between the velocity and pressure signals, while that of \(\overline{up}\) is not.

An experimental study is conducted assessing the performance of an ejector together with an 8:1 aspect ratio rectangular nozzle with the eventual goal of noise reduction for jet engines. Wall static pressure and Pitot probe surveys are conducted to evaluate the performance of the ejector, and sound pressure level measurements are made to assess the impact on noise radiation. It is found that addition of vortex generating tabs at the lip of the nozzle causes large increases in secondary flow entrainment. The baseline ejector (without tabs) often encounters flow resonance with accompanying tones. The tabs have the additional benefit of eliminating those tones. In most cases tried so far, pockets of high-speed fluid remain unmixed. Since jet noise scales as velocity to the eighth power, such ‘hot spots’ defeat the noise reduction goal. In some cases, there is a reduction in noise amplitudes in the mid-frequency range (5-30 kHz), however, an increase occurs on the low frequency end apparently due to flow unsteadiness. This together with a high frequency noise increase caused by the tabs results in minimal reductions in the overall sound pressure level. The focus of ongoing and future efforts is to achieve sufficient mixing and desirable noise reduction while keeping the hard-ware short and lightweight.

An adaptive Extended Kalman Filter for monitoring and estimating key aircraft flight parameters

This study was motivated by the need for improved understanding of blunt trailing-edge compressor airfoil flow fields. The objective was to provide data that could be used to assist the development of computational procedures for predicting such flows. A large-scale, low subsonic Mach number, wind tunnel simulation of a compressor airfoil trailing-edge flow field was conducted using a flat-plate test model and laser Doppler velocimetry for flow field definition. Of potential importance in the numerical modeling of the flow was the finding that outer flow velocity profiles in the near wake were nearly identical, with viscous interaction effects confined to a region near the wake centerline having a thickness and length comparable to that of the trailing-edge thickness. Qualitative agreement with circular cylinder near-wake data and an observed lack of dependence of results on a change in plate boundary-layer thickness suggest that the flow is not strongly dependent on boundary-laye r thickness at separation. Periodic vortex shedding was encountered and shown to affect base pressure significantly. The associated strong transverse velocity fluctuations would be expected to be the dominant mechanism for mixing out the velocity defect in the initial wake region.

This study was motivated by the need for improved understanding of blunt trailing-edge compressor airfoil flow fields. The objective was to provide data that could be used to assist the development of computational procedures for predicting such flows. A large-scale, low subsonic Mach number, wind tunnel simulation of a compressor airfoil trailing-edge flow field was conducted using a flat-plate test model and laser Doppler velocimetry for flow field definition. Of potential importance in the numerical modeling of the flow was the finding that outer flow velocity profiles in the near wake were nearly identical, with viscous interaction effects confined to a region near the wake centerline having a thickness and length comparable to that of the trailing-edge thickness. Qualitative agreement with circular cylinder near-wake data and an observed lack of dependence of results on a change in plate boundary-layer thickness suggest that the flow is not strongly dependent on boundary-laye r thickness at separation. Periodic vortex shedding was encountered and shown to affect base pressure significantly. The associated strong transverse velocity fluctuations would be expected to be the dominant mechanism for mixing out the velocity defect in the initial wake region.