Cryogenic Wind Tunnel Research Articles

Transonic aerodynamics including strong effects from heat addition

Gasdynamic phenomena in transonic flows caused by the phase transition of the fluid components of vapor/carrier gas mixtures and pure vapors have been investigated in theory and experiment. The dominating parameters, the cooling rate of the expansion and the reservoir conditions (vapor pressure) are varied to investigate the coupled process of the nonequilibrium phase transition after homogeneous nucleation and the equilibrium condensation in flows near a Mach number of unity. The numerical code is applied to compute transonic flows of water vapor/carrier gas mixtures in indraft wind tunnels and in atmospheric flight, flows of nitrogen vapor in cryogenic wind tunnels or shock tubes and the equilibrium condensation process in flows over airplane wing sections. The computation of the inviscid flow field is based on an explicit finite volume method that solves the time-dependent 2-D Euler equations linked with the classical nucleation theory and microscopic or macroscopic droplet growth laws. Turbulent boundary layer calculations demonstrate viscous effects and the development of the nonequilibrium phase transition in shear layers. Emphasis is given to supercritical rates of the heat release and shocks inside the nucleation zone and aerodynamical shocks with evaporation of the condensate. The main contribution is achieved from the phase transition in the inviscid flow with rates of heat addition q/cpT01 typically <10%. Nevertheless, transonic flow fields become seriously affected and the pressure drag and lift of airfoils change up to 60%. The sign of these variations changes sensitively with the free-stream Mach number and the angle of attack. Atmospheric flight condensation processes develop near equilibrium and cause a significant increase in the pressure drag. Computations on the basis of given heat source distributions show that homogeneous nucleation initiates heat release to the flow just in the most sensitive region over the airfoils.

防衛大学校低温風洞の冷却過程の改善について

One of the most critical stages of operation for an externally insulated cryogenic wind tunnel is the cooldown stage. The NDA cryogenic wind tunnel is such a tunnel, and has suffered from the rather inefficient cryogenic operation due to its poor cooldown characteristics. To correct this defect, the original total pressure control system and the cooldown preocedure were modified. The test results with the new ones showed that the modified system and preocedure save substantial amount of liquid nitrogen and time for the cooldown.

Boundary-layer transition-detection in a cryogenic wind tunnel usinginfrared imaging

Cryogenic wind tunnels are currently the only option available to test models of medium to large transport airplanes at high Reynolds numbers identical to those encountered in flight. This matching in Reynolds numbers is required for reproducing the flow viscous effects, most notably the laminar to turbulent boundary-layer transition. Infrared imaging is particularly attractive for transition detection in cryogenic wind tunnels because it is nonintrusive, fast, and provides a global view of the boundary-layer status on the model. An experimental method using a commercial 8- to 12-p infrared imaging system was developed for transition detection in cryogenic wind tunnels. So far, transition has been detected at temperatures down to 170 K. At this temperature, tunnels with a pressurization capability of only a few atmospheres can generate transonic flows at Reynolds numbers beyond 3 X108 per meter. Nomenclature M = Mach number Pt = total pressure R/m = Reynolds number per meter Rc = chord Reynolds number Tt = total temperature a = angle of attack ATt = total temperature step set in the wind-tunnel flow

The cryogenic wind tunnel

Until recently engineers have been unable to reach full scale Reynolds number in most wind tunnel tests. The cryogenic wind tunnel has been introduced to provide the aerospace community with the means to test models at near-full-scale Reynolds numbers, satisfying a particular need at transonic speeds. The background to the need for high Reynolds number wind tunnels is outlined together with options. The main advantages of the cryogenic option are highlighted which led to this type being adopted for transonic testing. The novel technology is described together with brief descriptions of several of the more major tunnel projects.

Cryogenic transonic wind tunnels and the condensation of nitrogen

A brief tutorial on the need for Reynolds number similarity and the advent of cryogenic transonic wind tunnels is presented. Experimental results of nitrogen condensation in nozzles are collected and related to the flow in the wind tunnels. New theoretical approaches to a solution of the condensation problem in the supersaturated state are proposed.

Calculation of support interferences on the aerodynamic coefficients for a windtunnel calibration model

SummaryAn AGARD calibration model has been tested in the subsonic cryogenic windtunnel (KKK) of DLR Köln, model support interferences are calculated in the form of corrections to the aerodynamic coefficients. Two different model support systems are investigated: the model mounted on a horizontal sting (rear sting), and the model mounted on a vertical sting (ventral sting). Since for these configurations earlier experiments already exist, the corrections obtained are applied to these measurements for further verification. Furthermore the sting influences on the longitudinal static stability of the model are investigated in more detail.A 3D-panel method is used which allows simultaneous calculation of several displacing and lifting bodies of nearly arbitrary shapes in the flow. The aerodynamic coefficients are obtained by numerical integration of the surface pressure distribution on the model.

A review of rigid body response on sting supported models at high angles of incidence

The new requirement to test wind tunnel models of combat aircraft at high angles of incidence and high kinetic pressures has led to a review of the factors controlling the model stability. The review suggested that dangerous motions might occur (possibly without prior warning) on models at high angles of incidence unless special preventive measures were taken. An internal tuned damper and balance bump stops were recommended to limit the responses. The bump stops would also prevent the moment limits of the strain gauge balance from being exceeded. The effectiveness of both devices was confirmed by tests on a swept wing model which experienced dangerous bending oscillations in a vertical plane at a Mach number of 0.50 in the incidence range from about 27–29° together with dangerous yawing oscillations in a horizontal plane above an incidence of about 35°. Further research is recommended to ensure the safety of other models. For sting supported models in a conventional wind tunnel, it is shown by analysis that the structural damping in the sting bending mode needs to be about 4 to 6% critical damping. In a cryogenic wind tunnel corresponding levels would need to be 7 to 10% critical damping because of the possibility of increased negative aerodynamic damping relative to ambient conditions.

Turbulence measurements and noise generation in a transonic cryogenic wind tunnel

A high-frequency combination probe was used to measure dynamic flow quality in the test section of the NASA Langley 0.3-m Transonic Cryogenic Tunnel. The probe measures fluctuating stagnation (total) temperature and pressure, static pressure, and flow angles in two orthogonal planes. Simultaneous measurements of unsteady total temperature and pressure were also made in the settling chamber of the tunnel. The data show that the stagnation temperature fluctuations remain constant, and the stagnation pressure fluctuations increase by a factor of two, as the flow accelerates from the settling chamber to the test section. In the test section, the maximum rms value of the normalized fluctuating velocity is 0.7 percent. Correlation coefficients failed to show vorticity, entropy, or sound as the dominant mode of turbulence in the tunnel.

Convective heat transfer research using a cryogenic environment

It is difficult to experimentally study the convective heat exchange from large objects with reduced scale models in a controlled laboratory environment because it is not possible to generate the large Reynolds and Grashof numbers which are required. Furthermore, the convective heat exchange is difficult to separate from the radiative heat transfer in many investigations. In this paper, the use of a cryogenic wind tunnel is shown to be a viable means of performing such investigations. The many advantages of using a cryogenic environment are established and a variable ambient temperature cryogenic heat transfer tunnel, which was constructed at the University of Illinois at Urbana-Champaign, is described. Representative experimental results are also presented.

An optical angle of attack sensor

A major source of transonic and supersonic wind-tunnel test data uncertainty are angle-of-attack-measurement errors caused by unknown sting and balance deflections under load. Since dynamic loads in pressurized or cryogenic wind tunnels generally exceed those in conventional low-speed atmospheric wind tunnels, the need to account for these distortions during model testing is even more acute. A novel laser-based instrument for the in-situ measurement of wind-tunnel-model angle of attack that enables continuous, time-dependent measurements to be made without signal dropout is described. Proof-of-concept experiments, along with the results of recent measurements conducted at the NASA Ames 9-ft*7-ft supersonic wind tunnel, are presented. Experiments were also conducted to determine the reliable range, sensitivity, and long-term stability of the instrument. The results show that 0.01 degrees sensitivity can be achieved and that optical and detector packaging requirements are less stringent than those for current tilt-sensor or accelerometer model installations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The effect of a wake splitter plate on the flow amound a circular cylinder.

Experiments were carried out using a circular model with a wake splitter plate having length ratio (L/d)=1/6, 1 or 3 in the Reynolds number range of 5×104≤Re≤107 using a cryogenic wind tunnel. The resulting variations of pressure distributions, drag coefficients, back pressure coefficients, the minimum values of pressure coefficients and Strouhal numbers with the length of wake splitter plate are presented. The effect of the wake splitter plate on the drag and Strouhal number are shown to change depending on the Reynolds number range and on the length of the wake splitter plate. Effects of the wake splitter plate on the reduction of the drag coefficient is most remarkable in the subcritical Reynolds number range. In the supercritical Reynolds number range the wake splitter plate serves to suppress the separation bubble. In the transcritical Reynolds number range the effects of the wake splitter plate can hardly be recognized.

防衛大学校低温風洞の特性 （第１報） 手動制御による運転

A 2-dimensional, small high speed cryogenic wind tunnel was constructed at National Defense Academy (N. D. A.) in 1985, using the stainless steels of SUS 304 and SCS 13 as materials of the pressure shell. The features of the cryogenic tunnel and its operation procedures are described. The initial operational tests were intensively performed to refine the general operation method to the optimum for the present tunnel with the original manual control systems. Those tests showed that the original control systems were fairly acceptable, but had to be modified to automatic controls for more precise control of the tunnel flow conditions at cryogenic temperature range and expanding its actual operational envelope.

Cryogenics at the university of southampton: a review

This Paper reviews the considerable breadth of activity in cryogenics across the campus of the University of Southampton. While this activity is focussed on the Institute of Cryogenics which was created in 1979, a very great deal of collaborative work is described involving the Departments of Chemistry and Physics in the Faculty of Science, the Departments of Aeronautics and Astronautics, Civil Engineering, Electrical Engineering, Electronics and Computer Science, and Mechanical Engineering in the Faculty of Engineering and Applied Science, and the Faculties of Mathematics and Medicine. The development of cryogenics from the early 1950s is described and traces the growing impact of the Southampton findings in cryogenic fluid mechanics on vapour cooled shields, dewar and cryostat design, storage instabilities in large tanks, carbon loaded multi-layer insulations, rotating helium at 3000 rev min − and cryosurgical probes. Current activity described includes the rapid expansion in work on high T c superconductors, the development of cryogenic and frost proof concrete, boiling and condensation heat transfer in liquid nitrogen, magnetic separation, refrigerators, pipe freezing, cold electronics, cryogenic wind tunnels and mathematical modelling of cryogenic convection.

Cryogenic wind tunnel research: a global perspective

The development of cryogenic wind tunnels is reviewed and 13 cryogenic wind tunnels currently operating in England, France, Germany, Japan, and the U.S. are described. A table illustrating the characteristics of these tunnels is presented, including test gases, test section sizes, speed ranges, stagnation pressure and temperature, and running time. The research conducted using the various wind tunnels is outlined and the operation of each of the tunnels is considered.

Characteristics of hot wire anemometer in low temperature flow. (Effect of aspect ratio).

A cryogenic wind tunnel, in which liquid nitrogen is sprayed into the closed wind tunnel body to get low temperature and high pressure gas, is used to produce high Reynolds number flow in fluid dynamic measurement. In this case, if we want to use a hot wire anemometer to measure flow velocity, the calibration curve, i.e. the relation of output voltage and wind speed must be obtained. Under these low temperature and high pressure conditions we must use thick tungsten wire. The effect of heat conduction through both ends is also important. Several investigations have been conducted to determine the character of hot wire placed in atmospheric air flow. In this study, an analysis of the relation of output voltage and flow velocity of a constant temperature type cot wire anemometer by changing its length and diameter was made for various values of temperature and pressure of nitrogen gas using a small cryogenic wind tunnel. It was concluded that the nondimensional relation acquired in the atmospheric condition can be extended in the cryogenic condition.

Design of a Feedback Controller for a Cryogenic Windtunnel

A controller design is presented for a cryogenic windtunnel. The nonlinear multi-input multi-output model with state dependent time delays in input variables is first simplified: For the simplified model a suitable choice of controller structure is straightforward. Values for the controller coefficients are first obtained by pole assignment and are then taken as initial values for several controller designs using optimization of a vector performance index. The problem of obtaining satisfactory performance with a simplest possible controller structure (e.g. using fixed gain PI-control) is investigated. All control designs are evaluated by nonlinear simulations.

Natural Convection From Isothermal Cubical Cavities With a Variety of Side-Facing Apertures

An experimental investigation of heat transfer by natural convection from a smooth, isothermal cubic cavity with a variety of side-facing apertures is described in this paper. The study was motivated by the desire to predict the convective loss from large solar thermal-electric receivers and to understand the mechanisms which control this loss. Hence, emphasis is placed on the large Rayleigh number, Ra, regime with large ratios of the cavity wall temperature Tw to the ambient temperature T∞. A cryogenic wind tunnel with test section temperatures which are varied between 80 K and 310 K is used to facilitate deduction of the influences of the relevant parameters and to obtain large temperature ratios without masking the results by radiative heat transfer. A 0.4-m cubic cavity, which is mounted in the side wall of this tunnel, is used. The area of the aperture Aa and its location are key variables in this study. The data which are presented cover the ranges: 1 &lt; Tw/T∞ &lt; 3, L2/18 ≤ Aa ≤ L2, and 3 × 107 &lt; Ra &lt; 3 × 1010.

Exploratory flutter test in a cryogenic wind tunnel

A model consisting of a rigid wing with an integral, flexible beam support that was cantilever mounted from the wall in the NASA LaRC 0.3-m transonic cryogenic tunnel was used in a flutter analysis study. The wing had a rectangular planform of aspect ratio 1.5 and a 64A010 airfoil. Various considerations and procedures for conducting flutter tests in a cryogenic wind tunnel were evaluated. Flutter onset conditions were established from extrapolated subcritical response measurements. A flutter boundary was determined at cryogenic temperatures over a Mach number M range from 0.5 to 0.9. Flutter was obtained at two different Reynolds numbers R at M = 0.5 (R = 4.4 and 18.4 x 10 to the 6th power) and at M = 0.8 (R = 5.0 and 10.4 x 10 to the 6th power). Flutter analyses using subsonic lifting surface (kernel function) aerodynamics were made over the range of test conditions. To evaluate the Reynolds number effects at M = 0.5 and 0.8, the experimental results were adjusted using analytical trends to account for differences in the model test temperatures and mass ratios. The adjusted experimental results indicate that increasing Reynolds number from 5.0 to 20.0 x 10 to the 6th power decreased the dynamic pressure by 4.0 to 6.5 percent at M = 0.5 and 0.8.

Mechanical behavior of 18 Ni 200 grade maraging steel at cryogenic temperatures

A comprehensive study was conducted to characterize the mechanical behavior of 18 Ni 200 grade maraging steel for cryogenic applications in the National Transonic Facility. Tensile, fatigue, impact, and fracture toughness properties were determined at room and cryogenic temperatures. Experimental variables included product form, specimen orientation, and variation in metallurgical condition accomplished with a grain refining heat treatment. Room temperature tensile yield strength was approximately 200 ksi, while the yield strength at -275 F was approximately 260 ksi. Charpy V-notch energy absorption values and fracture toughness values of 18 Ni steel were found to be dependent on temperature, product form, orientation, and metallurgical condition. Fracture toughness values ranged from 80 to 113 ksi-sq rt in. at room temperature and from 67 to 90 ksi-sq rt in. at -275 F. The results of this study indicate that 18 Ni 200 grade maraging steel exceeds the strength criterion of 150 ksi minimum yield strength for use in cryogenic wind tunnel models but is marginal with respect to the 85 ksi sq rt in fracture toughness criterion at -275 F.

Cryogenic tunnel measurement of total temperature and pressure

A newly developed, 3-mm-diam, dual hot-wire aspirating probe was used to measure the time-resolved stagnation temperature and pressure in a transonic cryogenic wind tunnel. Measurements were taken in the freestream of the settling chamber and test section. Data were also obtained in the unsteady wake shed from an airfoil oscillating at 5 Hz. The investigation revealed the presence of large fluctuations in the settling chamber occuring at the blade passing frequency of the driving fan of the tunnel. These fluctuations decrease at the test section. The rms value of the fluctuating stagnation pressure decreased from 17.5 percent in the settling chamber to 3.7 percent in the test section. Fluctuating stagnation temperature decreased from 12.3 percent to 8.4 percent. Measurements in the wake of the oscillating airfoil showed a fluctuating stagnation temperature of as much as 42 K in rms value.