优化跨音速自适应壁试验段设计的试验研究

分析了在矩形截面试验段中三元模型试验时的洞壁干扰分布。讨论了为扩大二元柔壁自适应壁风洞中进行飞机模型试验时的无干扰区，较合适的试验段宽高比。用两个翼身组合体模型，在西北工业大学高速二元柔壁自适应风洞中作了变试验段宽高比为Ｂ／Ｈ＝１．０，１．２，１．４时的测压试验。两个模型都在德国宇航院ＨＫＧ高速风洞中作了对比试验，研究结果表明，Ｂ／Ｈ＝１．４的柔壁试验段截面较为合适。     

Stokes flow through a permeable tube

Pressure-driven Stokes flow through a circular tube with a permeable wall is considered as a model of blood flow through a capillary vessel. Fluid penetrates the tube wall over a test section according to Starling law relating the normal fluid velocity to the transmural pressure defined as the difference between the wall and the uniform ambient pressure. The problem is formulated using the integral representation for Stokes flow, and the solution is computed with high accuracy using a boundary-element method for specified values of the wall permeability and percentage of fluid escaping through the walls. The results illustrate the structure of the flow and validate the predictions of a model based on the assumption of locally unidirectional flow for sufficiently small permeability.     

Shock wave reflection off coupled surfaces

It has been shown that when a plane shock wave is reflected off a surface consisting of a 75-mm radius circular arc followed by a plane section inclined at 45°, it takes some time for the interaction to reach a pseudosteady reflection configuration. The current study extends this work at a constant Mach number of 1.346, with three compound walls, consisting of leading circular sections of 30, 50 and 75 mm radius, joined to a plane wall section. Testing was done at various wall angles for each of the test pieces. The reflected wave angle was measured and was found to increase along the plane wall section until it reached an asymptotic value, at which time pseudosteady flow was established. The asymptotic values are consistent with reflection off plane wedges and are independent of the leading radius. For lower wall angles which lead to Mach reflection the length required to reach pseudosteady flow increases as the wall angle increases to the pseudosteady transition angle. The reverse occurs when the final pseudosteady reflection is regular, in that as the wall angle increases the distance travelled to reach pseudosteady flow conditions decreases. Additional tests were conducted on a specimen consisting of a plane section at 60° wall angle with 30-mm radius circular arc sections at either end. It is demonstrated how the information from the two slope changes influences the shape of the reflected shock. The trajectories of two perturbations on the reflected shock arising from the joints between the circular sections and the plane wall show that the reflected wave remains linear between these two points, as it received no knowledge from either circular section until the perturbations from the upper and lower joints cross.     

Numerical simulation of the modulated flow pattern for vertical upflows by the phase separation concept

The multiphase heat transfer could be enhanced by creating thin liquid film on the wall. The phase separation concept is called due to the separated flow paths of liquid and gas over the tube cross section to yield thin liquid film. Our proposed heat transfer tube consists of an annular region close to the wall and a core region, interfaced by a suspending mesh cylinder in the tube. The heat transfer tube is a multiscale system with micron scale of mesh pores, miniature scale of annular region and macroscale of tube diameter and length. Great effort has been made to link from micron scale to macroscale. The Volume of Fluid (VOF) method simulates air/water two-phase flow for vertical upflow. The three-dimensional system was successfully converted to a two-dimensional one by using three equivalent criteria for mesh pores. The non-uniform base grid generation and dynamic grid adaption method capture the bubble interface. The numerical results successfully reproduce our experimental results. The numerical findings identify the following mechanisms for the enhanced heat transfer: (a) counter-current flow exists with upward flow in the annular region and downward flow in the core region; (b) void fractions are exact zero in the core region and higher in the annular region; (c) the liquid film thicknesses are decreased to 1/6–1/3 of those in the bare tube section; (d) the gas–liquid mixture travels much faster in the annular region than in the bare tube; (e) three-levels of liquid circulation exists: meter-scale bulk liquid circulation, moderate-scale liquid circulation around a single-elongated-ring-slug-bubble, and microliquid circulation following the ring-slug-bubble tails. These liquid circulations promote the fluid mixing over the whole tube length and within the radial direction. The modulated parameters of void fractions, velocities and liquid film thicknesses in the annular region and three-levels of liquid circulation are greatly beneficial for the multiphase heat transfer enhancement.     

An experimental investigation of the static pressure fluctuation mechanism for porous transonic wind tunnel wall configurations

An experimental investigation of the static pressure fluctuation generation mechanism was performed for different transonic wind tunnel test section perforated wall configurations. Different hole diameters and geometrical configurations were investigated. Most tests were carried out with isolated perforations, while some were done with a three hole, 16° perforation pattern. To suppress the oscillation amplitudes generated by perforations, splitter-plates as flow conditioning devices along the perforations were implemented on a large number of perforated transonic test section wall samples. It was found that all the hole configurations tested, regardless of diameter or shape, resonate at discrete frequencies which order themselves along several modes.     

二元自适应壁风洞实验技术研究

介绍了在柔壁自适应壁风洞中，进行大堵塞比翼型低、跨音速实验消除洞壁干扰的研究，叙述了西北工业大学低、跨音速柔壁自适应壁风洞实验的迭代方案和高亚音速一步调整方案，以及所进行的实验和计算验证。结果表明，本文提出的洞壁调整方案可以有效地消除二维柔壁自适应风洞中大堵塞比翼型实验的洞壁干扰。     

Rotation effects on a fully-developed turbulent pipe flow

A fully-developed turbulent pipe flow is allowed to pass through a rotating pipe section, whose axis of rotation coincides with the pipe axis. At the exit end of the rotating section, the flow passes into a stationary pipe. As a result of the relaxation of surface rotation, the turbulent flow near the pipe wall is affected by extra turbulence production created by the large circumferential shear strain set up by the rapid decrease of the rotational velocity to zero at the wall. However, the flow in the most part of the pipe is absent of this extra turbulence production because the circumferential strain is zero as a result of the solid-body rotation imparted to the flow by the rotating pipe section. The combined effect of these two phenomena on the flow is investigated in detail using hot-wire anemometry techniques. Both mean and turbulence fields are measured, together with the wall shear and the turbulent burst behavior at the wall. A number of experiments at different rotational speeds are carried out. Therefore, the effects of rotation on the behavior of wall shear, turbulent burst at the wall, turbulence production and the near-wall flow can be documented and analysed in detail.     

Anwendung der Tieftemperaturtechnik im strömungstechnischen Versuchswesen

Übersicht Die Anwendung der Tieftemperatur- oder Kryotechnik im Windkanalbau bringt im Vergleich zu dem bei Normaltemperatur betriebenen baugleichen Windkanal eine Reynoldszahlerhöhung bei gleichzeitig reduzierter Gebläseantriebsleistung. Der Preis hierfür ist jedoch eine zusätzliche Kälteleistung. Der vorliegende Bericht beschäftigt sich mit dem energetischen Aspekt der Kryotechnik im Windkanalbau. Unter Beschränkung auf die rein zur Abführung der Windkanal-Prozeßwärme notwendige Kälteleistung wird der kontinuierlich betriebene Windkanal der Göttinger Bauart und der Speicherwindkanal vom blow-down-Typ näher untersucht. Schließlich wird die Möglichkeit der Reduktion der Kälteleistung durch Verwendung schwerer Gase als Testgas diskutiert.

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Summary The application of cryogenics in windtunnel design offers an increase in Reynolds number simulation at simultaneously reduced drive power for the windtunnel compressor compared to a windtunnel driven at normal temperatures. The price, however, is an additional cryogenic power. The report concerns with the energetic aspect of cryotechnics in windtunnel technique. With restriction only to cryogenic power due to tunnel process-heat, the continuously running tunnel with closed circuit and the blow-down-storage tunnel are investigated. Finally, the possibility of reducing cryogenic power using heavy gases as test medium is discussed.

     

Bulk flow parameters in turbulent wall boundary layers near separation

Experiments were conducted in a turbulent boundary layer near separation along a flat plate. The pressure gradient in flow direction was varied such that three significant boundary layer configurations could be maintained. The flow in the test section thus had simultaneously a region of favourable pressure gradient, a region of strong adverse pressure gradient with boundary layer separation and a region of reattached boundary layer. Specially designed fine probes facilitated the measurements of skin friction and velocity distribution very close to the wall. Bulk flow parameters such as skin friction coefficient C _f, Reynold's number Re_δ2 and shape factors H and G, which are significant characteristics of wall boundary layers were evaluated. The dependence of these parameters on the Reynolds number and along the test section was explored and the values were compared with other empirical and analytical formulae known in the literature.     

跨音速翼型上的激波／边界层干扰自适应控制计算

在激波区使用自适应壁对跨音速翼型的激波／边界层的相互作用（干扰）进行控制，可改变机翼的气动性能，这种被动控制可通过在翼型的激波区开一凹腔，其上覆盖一弹性橡胶膜柔壁来，本文给出用Ｎａｖｉｅｒ－Ｓｔｏｋｅｒ方程数值模拟这一自适应控制翼型的跨音速粘性绕流，提出了一个适应于本特殊情况（物面边界局部地区在求解过程中有变化）的处理办法。并探讨了自适应柔壁对当代跨音速翼绕流的影响。     

Determination of the measuring position in laser-Doppler anemometry

The present paper is concerned with the determination of the measuring position of a laser-Doppler anemometer (LDA) relative to a wall. The proposed method is based on the finding that the output of a hot-wire anemometer increases when the wire, which is mounted in quiescent air parallel to the wall, is brought closer than 800 m to the wall. For given hot-wire anemometer parameters, the hot-wire anemometer output voltage depends on the wall material and the wire distance from the wall. After suitable calibration for the wall material of the test section, the anemometer reading in a test rig can be used to find the wire position. Moving the measuring volume of a LDA-system across the wire yields an output voltage variation of the LDA-photomultiplier showing a Gaussian shape. When the maximum output voltage is reached, the centre of the measuring control volume is located at the centre of the wire and, hence, the location of the LDA-measuring position is known. All position measurements for the LDA-system are then taken relative to this point using the scale of the LDA-traversing system. If optical effects of transparent test section walls are eliminated by employing refractive index matched liquids, there are other ways to find the measuring position of a laser-Doppler anemometer relative to a wall. One such method and its application to the study of the turbulent near wall flow in a pipe is described in this paper.     

High enthalpy nozzle flow sensitivity study and effects on heat transfer

The sensitivity of the flow along the nozzle and in the test section of high enthalpy wind tunnels to the thermochemical response of the nozzle expansion process, as well as effects on the pressure and heat transfer distributions over the Electre blunt cone standard test model, are examined in the framework of properly characterizing the test section flow field in such facilities. Particularly sensitive to the thermochemical behaviour of the nozzle flow, in the facilities under consideration, are the static pressure, static temperature and Mach number, whereas stagnation point (pitot) pressure and heat transfer data or freestream velocity are inadequate for the characterization of the thermochemical state of the flow. The Electre and nozzle wall pressure data in the F4 arc jet wind tunnel suggest, in contrast to nonequilibrium computations, that the flow in the F4 nozzle is close to equilibrium. In the HEG and, to some extent, the T5 piston-driven shock tunnels, there are indications that significant heat losses occur in the reservoir. Lastly, simple semi-empirical formulations for stagnation point heating are shown to perform reasonably well in high enthalpy flow conditions.     

An analytical theory of heated duct flows in supersonic combustors

One-dimensional analytical theory is developed for supersonic duct flow with variation of cross section, wall friction, heat addition, and relations between the inlet and outlet flow parameters are obtained. By introducing a selfsimilar parameter, effects of heat releasing, wall friction, and change in cross section area on the flow can be normalized and a self-similar solution of the flow equations can be found. Based on the result of self-similar solution, the sufficient and necessary condition for the occurrence of thermal choking is derived. A relation of the maximum heat addition leading to thermal choking of the duct flow is derived as functions of area ratio, wall friction, and mass addition, which is an extension of the classic Rayleigh flow theory, where the effects of wall friction and mass addition are not considered. The present work is expected to provide fundamentals for developing an integral analytical theory for ramjets and scramjets.     

Boiling flow simulations on adaptive octree grids

Boiling flow simulations are conducted on adaptive octree grids. A phase change model consistent with the mixture formulation, in conjunction with the Volume-of-Fluid (VOF) model, is used to track the liquid–vapor interface. Test cases including Rayleigh Taylor instability and bubble growth in a uniform superheat are conducted to validate the phase change model on adaptive grids. The validated model is then used to conduct film boiling simulations on both two-dimensional and three-dimensional adaptive grids. The average wall Nusselt number agrees well with the widely accepted correlations of Berenson (1961) and Klimenko (1981) and Klimenko and Shelepen (1982) for film boiling on a horizontal surface. For the test cases presented, the efficiency of the adaptive technique, as measured by the adaptive mesh refinement (AMR) efficiency, is mostly in the range of 50–80%. Although this efficiency is a function of the nature and dimensionality of the problem, this range of efficiency is comparable to those obtained in the simulations of primary jet atomization conducted by Fuster et al. (2009). This work opens the prospect of conducting more realistic (three-dimensional) multi-modal boiling flow simulations, and problems of similar complexity, in an efficient manner.     

Manipulation of the reverse-flow region downstream of a fence by spanwise vortices

The experimental investigation of a turbulent separated flow over a fence is presented. By introducing a periodic disturbance upstream of the separation region in front of the fence, the time averaged length of the separation region downstream of the fence was reduced by as much as 40%. Two types of flow manipulation were applied: an oscillating cross-flow with zero net mass-flux through a spanwise slot in the floor of the test section and a spanwise oriented, oscillating spoiler. The cross-flow was generated by a loudspeaker system connected to a chamber underneath the spanwise slot. Both types of flow manipulation generate spanwise vortices at the fence that convect into the region downstream of the fence where they enhance the mixing in the shear layer and reduce the time mean length of the reverse-flow region downstream of the fence. Velocity profiles phase averaged with respect to the forcing frequency and phase triggered flow visualisations show that the spanwise vortices cause the long reverse-flow region of the unmanipulated flow to break up into separate smaller regions. While the time mean length of the reverse-flow region is reduced in the manipulated case, the length of the region where instantaneous reverse-flow occurs is not changed. The data presented include wall pulsed-wire measurements of the wall shear-stress and its turbulent fluctuations, and LDA measurements of the streamwise and the wall-normal velocity components and turbulent stresses.     

Automatic liquid crystal thermography for transient heat transfer measurements in hypersonic flow

A technique has been developed to measure surface heat transfer on windtunnel models in hypersonic flow based on the colour response of encapsulated thermochromic liquid crystals. The method supplies results of a superior spatial resolution at experimental uncertainties comparable to traditional methods. The approach is different from other liquid crystal applications in several key areas. It combines the calibration of the liquid crystal coating with the actual mesurement and therefore allows for an efficient experiment. The method is automated in most steps involved. Results are shown for the flow over an axisymmetric compression corner at Mach 5 and compared with surface thermocouple measurements.     

The hypersonic Mach number independence principle in the case of viscous flow

The hypersonic Mach number independence principle of Oswatitsch is important for hypersonic vehicle design. It explains why, above a certain flight Mach number (M _∞ ≈ 4−6, depending on the body shape), some aerodynamic properties become independent of the flight Mach number. For ground test facilities this means that it is sufficient for the Mach number in the test section to be high enough, that Mach number independence exists. However, the principle was derived for calorically perfect gas and inviscid flow only. In this paper a theoretical study for blunt bodies in the case of viscous flow is presented. We provide numerical results which give insight into how attached viscous flow behaves at high Mach numbers. The flow past an axisymmetric configuration is analysed by applying a coupled Euler/second-order boundary-layer method. Wall boundaries are treated by assuming an adiabatic or radiation-adiabatic wall for laminar flow. Calorically perfect or equilibrium air is accounted for. Lift, drag, and moment coefficients, and lift-to-drag ratios are given for several combinations of flight Mach number and altitude, i.e. Reynolds number. For blunt bodies considered here, which are pressure dominated, Mach number independence occurs for the adiabatic wall, but not for the radiation-adiabatic wall assumption.     

Shock wave attenuation by grids and orifice plates

The interaction of weak shock waves with porous barriers of different geometries and porosities is examined. Installing a barrier inside the shock tube test section will cause the development of the following wave pattern upon a head-on collision between the incident shock wave and the barrier: a reflected shock from the barrier and a transmitted shock propagating towards the shock tube end wall. Once the transmitted shock wave reaches the end wall it is reflected back towards the barrier. This is the beginning of multiple reflections between the barrier and the end wall. This full cycle of shock reflections/interactions resulting from the incident shock wave collision with the barrier can be studied in a single shock tube test. A one-dimensional (1D), inviscid flow model was proposed for simulating the flow resulting from the initial collision of the incident shock wave with the barrier. Fairly good agreement is found between experimental findings and simulations based on a 1D flow model. Based on obtained numerical and experimental findings an optimal design procedure for shock wave attenuator is suggested. The suggested attenuator may ensure the safety of the shelter’s ventilation systems.     

Flow with heat transfer in the presence of phase transitions on the wall of an annular channel

A solution is presented to the problem of the laminar flow of a heat-transfer vapor in an annular channel of constant cross section in the presence of a liquid film on the outer wall and heating through the inner wall of the channel. The results of test calculations for water vapor are given. The obtained results are analyzed, and it is shown that they make it possible to establish a number of characteristic features of the process, in particular, the possible existence of a self-similar solution.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 143–146, May–June, 1981.     

超临界翼型风洞实验的侧壁干扰研究

本文对模型周围的侧壁附面层抽吸,研究跨音速二元风洞的侧壁干扰。模型的展长大于风洞的宽度,其中央剖面有测压孔,在风洞实验段中可沿展向滑移,使测压剖面相对于风洞的对称平面的展向位置取不同的值。实验表明:在超临界情况,当对模型周围侧壁附面层进行抽吸时,气动力的展向均匀性改善,翼型上的激波向后移。