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Combined effects of unsteady wake and free-stream turbulence on turbine blade film cooling with laid-back fan-shaped holes using PSP technique
摘要： Detailed film cooling effectiveness distribution for a gas turbine blade under the effects of unsteady wakes and oncoming free-stream turbulence intensities was obtained using pressure sensitive paint (PSP) technique. Tests were performed on a linear cascade at Reynolds number of 3.85 × 10^5 based on the blade chord at cascade exit. Upstream unsteady wakes were simulated using a spoke-wheel type wake generator. The test blade has three rows of compound angled cylindrical film holes at the leading edge, five rows of laid-back fan-shaped holes on the pressure surface and three rows of laid-back fan-shaped holes on the suction surface. The wake Strouhal number was varied from 0 to 0.36 and three mass flux ratios were determined. The oncoming free-stream turbulence intensities are 2.7% and 26.9%, respectively. Results show that the effect of the mass flux ratio on the film cooling effectiveness decreases under the high turbulence intensity and unsteady wake conditions. In most regions of the blade surface, the film cooling effectiveness decreases with the increase of wake Strouhal number, and the free-stream turbulence superimposed on the unsteady wake reduces the film cooling effectiveness further. The effect of the unsteady wake decreases under the high free-stream turbulence conditions.
关键词： Turbulence intensity,Film cooling effectiveness,PSP,Wake,Mass flux ratio,Turbine blade,Strouhal number,Laid-back fan-shaped hole
更新于2025-09-23 15:23:52
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The First Solar Seeing Profile Measurement with Two Apertures and Multiple Guide Regions
摘要： Ground-based observations suffer from atmospheric turbulence perturbations, which seriously degrade the image quality. The seeing pro?le associated with the turbulence is critical to characterize an astronomical site. The optimal design and performance estimation of future solar ground-layer adaptive optics (GLAO) and multi-conjugate adaptive optics (MCAO) heavily rely on our knowledge of the seeing pro?le at a speci?c site. Many current optical seeing pro?le measurement techniques require one to use a large solar telescope for that purpose. The development of a portable instrument to measure and characterize the seeing pro?le is thus highly needed, in particular for testing potential new sites or for the regularly monitoring of the seeing condition at existing sites. Recently, we proposed the Advanced Multiple Aperture Seeing Pro?ler (A-MASP), which uses multiple small telescopes and multiple regions of interest (ROIs) on the solar surface to measure the seeing pro?le up to an altitude of 30 km. Here, we report our recent proof-of-concept observation run of the A-MASP technique with the Dunn Solar Telescope (DST) of the National Solar Observatory (NSO). We found that the Fried parameter, r0, was about 12 cm at the observed wavelength of 630 nm in the early morning and that there were three main turbulence layers. The strongest one was the mix layer near the ground. We observed the evolution of the top of the mix layer and found that it can rise to about 1.5 km in about 18 min, which is consistent with the theory of daytime boundary layer evolution. Another turbulence layer was observed from 8 to 15 km, which is at the top of the convective layer. Comparing an instrument with two sub-apertures with a real A-MASP instrument, we found that they should lead to similar results except for the altitude h = 0.
关键词： Instrumentation and data management,Turbulence
更新于2025-09-23 15:23:52
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Effect of anisotropic non-Kolmogorov turbulence on the evolution behavior of Gaussian Schell-model vortex beams
摘要： The effect of anisotropic non-Kolmogorov turbulence on the evolution behavior of average intensity and coherent vortices for Gaussian Schell-model (GSM) vortex beams is investigated. Based on the extended Huygens–Fresnel principle and power spectrum of the anisotropic non-Kolmogorov turbulence, the analytical expressions for the cross-spectral density and average intensity of GSM vortex beams propagating through anisotropic non-Kolmogorov turbulence are obtained. The evolution behavior of intensity and coherent vortices for GSM vortex beams in anisotropic non-Kolmogorov turbulence has been discussed in detail by numerical simulation. The results shown that the evolution behavior of coherent vortices and intensity profile depends on the effective anisotropic factor, generalized exponent factor and structure constant of anisotropic non-Kolmogorov turbulence, as well as the beam parameters, such as beam waist, wave length and correlation length.
关键词： Gaussian Schell-model vortex beams,Anisotropic non-Kolmogorov turbulence,Evolution behavior of coherent vortices
更新于2025-09-23 15:23:52
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[IEEE 2018 OCEANS - MTS/IEEE Kobe Techno-Ocean (OTO) - Kobe, Japan (2018.5.28-2018.5.31)] 2018 OCEANS - MTS/IEEE Kobe Techno-Oceans (OTO) - A High Dynamic Range in Situ Flow Sensor
摘要： High dynamic range and high accuracy flow sensor is a highly desirable device in quantifying mixing in the atmosphere and the ocean, which is critical in our understanding of energy dissipation and flux studies. We discuss a design that utilizes only a single point sensor in different angles, based on our novel oriented temperature Fabry-Perot using interferometry approach. We report the sensitivity of a high-dynamic range sensor head orientation in such configuration. We discuss initial configuration, data collection, processing, analysis and calibration including sensor orientation for future deployment.
关键词： Fabry-Perot interferometer,flow meter,turbulence,kinetic energy dissipation,fiber optics
更新于2025-09-23 15:23:52
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Observations of optically active turbulence in the planetary boundary layer by sodar at the Concordia astronomical observatory, Dome C, Antarctica
摘要： Aims. An experiment was set up at the Concordia station in Antarctica during the winter-over period in 2012 to determine the behaviour of atmospheric optical turbulence in the lower part of the atmospheric boundary layer. The aim of the experiment was to study the influence of turbulence and weather conditions on the quality of astronomical observations. The Concordia station is characterised by the high quality of astronomical images thanks to very low seeing values. The surface layer in the interior of Antarctica during the winter is very stably stratified with the differences of temperature between the surface and the top of the inversion, which reach 20?35?C. In spite of this strong static stability, considerable thermal optically active turbulence sometimes occurs and extends to several tens of metres above the surface, depending on weather conditions. It is important to know the meteorological characteristics that favour good astronomical observations. Methods. The optical measurements of the seeing made by differential image motion monitors installed at two levels of 8 and 20 m were accompanied by observations of turbulence in the lowest one hundred meters. Turbulence was detected and evaluated using a high-resolution sodar developed specially for this purpose. The statistics of some relevant meteorological variables including the long-wave downward radiation, which indicates cloudiness, were determined. Results. Typical patterns of the vertical and temporal structure of turbulence shown by sodar echograms were identified, analysed, and classified. The statistics of the depth of the surface-based turbulent layer and the turbulent optical factor for different height layers are presented together with the seeing statistics. We analysed the dependence of both seeing and integral turbulence intensity within the first 100 m on temperature and wind speed. Conclusions. Seeing and turbulence intensity in the atmospheric boundary layer appear to be correlated. The best values of the seeing (<1 arcsec) are observed when the sodar shows very low turbulence intensity. The main contribution to the image distortion is due to turbulence generated within the lowest 30?50 m near the surface. The presented statistics of the vertical distribution of the atmospheric optical turbulence can be used to determine the optimal location for astronomical instruments.
关键词： turbulence,site testing,atmospheric effects
更新于2025-09-23 15:23:52
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Error performance of optical wireless communication systems exercising BPSK subcarrier intensity modulation in non-Kolmogorov turbulent atmosphere
摘要： Subcarrier intensity modulation (SIM) scheme is preferred due to efficient bandwidth usage superiority over other modulation techniques such as on–off keying (OOK), pulse position modulation (PPM). In this paper, we investigate the bit error rate (BER) performance of optical wireless communication (OWC) system using binary phase shift keying (BPSK) SIM in non-Kolmogorov turbulent atmosphere. We pay attention to the weak turbulence conditions by using Rytov approximation and considering that the receiver is a PIN photodetector. Propagating beam type is Gaussian. It is seen that BER performance of the BPSK SIM OWC is significantly affected from non-Kolmogorov power law exponent, load resistor, responsivity of the PIN photodetector, bandwidth, beam source size, turbulence strength and noise factor.
关键词： Subcarrier intensity modulation,Optical wireless communication,Bit error rate,Atmospheric turbulence
更新于2025-09-23 15:23:52
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Frequency variations of solar radio zebras and their power-law spectra
摘要： Context. During solar ?ares several types of radio bursts are observed. The ?ne striped structures of the type IV solar radio bursts are called zebras. Analyzing them provides important information about the plasma parameters of their radio sources. We present a new analysis of zebras. Aims. Power spectra of the frequency variations of zebras are computed to estimate the spectra of the plasma density variations in radio zebra sources. Methods. Frequency variations of zebra lines and the high-frequency boundary of the whole radio burst were determined with and without the frequency ?tting. The computed time dependencies of these variations were analyzed with the Fourier method. Results. First, we computed the variation spectrum of the high-frequency boundary of the whole radio burst, which is composed of several zebra patterns. This power spectrum has a power-law form with a power-law index –1.65. Then, we selected three well-de?ned zebra-lines in three di?erent zebra patterns and computed the spectra of their frequency variations. The power-law indices in these cases are found to be in the interval between –1.61 and –1.75. Finally, assuming that the zebra-line frequency is generated on the upper-hybrid frequency and that the plasma frequency ωpe is much higher than the electron-cyclotron frequency ωce, the Fourier power spectra are interpreted to be those of the electron plasma density in zebra radio sources.
关键词： plasmas,Sun: radio radiation,turbulence
更新于2025-09-23 15:22:29
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Bandwidth-limited orbital angular momentum mode of Bessel Gaussian beams in the moderate to strong non-Kolmogorov turbulence
摘要： We investigate the effects of the moderate to strong fluctuation on the propagation of orbital angular momentum (OAM) modes carried by Bessel Gaussian beams in turbulent atmosphere. The analytic expression of the received probability of the signal and crosstalk OAM mode is derived based on the theories of extended Rytov and non-Kolmogorov turbulence. Our results show that turbulence with smaller non-Kolmogorov index, smaller inner-scale factor is more easily to induce OAM crosstalk between modes. With the increase of turbulence strength, the OAM spreads from adjacent modes to peripheral modes. Our results also indicate that the received signal intensity can be improved by use of Bessel Gaussian beams with small initial radii of beam, low OAM quantum number and long wavelength.
关键词： Bandwidth-limited mode,Non-Kolmogorov turbulence,Extended Rytov theory,Bessel Gaussian beam,Orbital angular momentum
更新于2025-09-23 15:22:29
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Optical orbital angular momentum under strong scintillation
摘要： The evolution of classical optical fields propagating through atmospheric turbulence is investigated under arbitrary conditions. We use the single-phase screen (SPS) method and the infinitesimal propagation equation (IPE), a multiphase screen (MPS) method, to compute the optical power fractions retained in an input Laguerre-Gauss (LG) mode or transferred to higher-order LG modes. Although they show the same trend while the scintillation is weak, the IPE and SPS predictions deviate when the strength of scintillation passes a certain threshold. These predictions are compared with numerical simulations of optical fields propagating through turbulence. The simulations are performed using an MPS model, based on the Kolmogorov theory of turbulence, for different turbulence conditions to allow comparison in both weak and strong scintillation. The numerical results agree well with the IPE results in all conditions, but they deviate from the SPS results for strong scintillation.
关键词： multiphase screen method,scintillation,infinitesimal propagation equation,atmospheric turbulence,Laguerre-Gauss modes,single-phase screen method,optical orbital angular momentum
更新于2025-09-23 15:22:29
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Autonomous Landing Control of Highly Flexible Aircraft based on Lidar Preview in the Presence of Wind Turbulence
摘要： This paper investigates preview-based autonomous landing control of a highly ?exible ?ying wing model using short range Lidar wind measurements in the presence of wind turbulence. The preview control system is developed based on a reduced-order linear aeroelastic model and employs a two-loop control scheme. The outer loop employs the LADRC (linear active disturbance rejection control) and PI algorithms to track the reference landing trajectory and vertical speed, respectively, and to generate the attitude angle command. This is then used by the inner-loop using H∞ preview control to compute the control inputs to the actuators (control ?aps and thrust). A landing trajectory navigation system is designed to generate real-time reference commands for the landing control system. A Lidar (light detection and ranging) simulator is developed to measure the wind disturbances at a distance in front of the aircraft, which are provided to the inner-loop H∞ preview controller as prior knowledge to improve control performance. Simulation results based on the full-order nonlinear ?exible aircraft dynamic model show that the preview-based landing control system is able to land the ?ying wing effectively and safely, showing better control performance than the baseline landing control system (without preview) with respect to landing effectiveness and disturbance rejection. The control system’s robustness to measurement error in the Lidar system is also demonstrated.
关键词： H∞ preview control,Highly ?exible aircraft,Lidar wind measurements,turbulence landing,autonomous landing control
更新于2025-09-23 15:22:29