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This paper investigates the unsteady aerodynamic characteristics of an oscillating flat plate and the NACA 0012 airfoil around the angle of attack (AoA) close to their static stall angle at a low Reynolds number, 3.2 × 104. The kinematic oscillatory motion is described by a sinusoidal function in which the oscillation frequency and amplitude are variable. Both experimental and numerical methods are applied in the two-dimensional space. The experiment aims at measuring the aerodynamic forces and the moment directly. For numerical simulation, the SST (Shear Stress Transport) gamma theta model is employed to solve the unsteady flow field and to compute the lift coefficients (CLs). Good qualitative agreement between the experimental and numerical results for CL is obtained, which demonstrates the feasibility of the modified RANS model in the flow transition case. In general, NACA 0012 is greatly influenced by the dynamic effect in contrast with the flat plate. For a given reduced frequency, the shape of the hysteresis loop of CL shows some distinguishing features; the process of flow reattachment of NACA 0012 is slower than that of the flat plate in the downstroke phase, so that a smooth transition of CL is observed; there are still vortices shedding from the trailing edge even at small angles of attack, which results in a local instability of CL. By studying the effects of the reduced frequency (K) and the amplitude, it is found that the AoA corresponding to the maximum CL is more sensitive to the former and the reduced pitch rate (a') is the main parameter determining the dynamic stall angle for both flat plate and NACA 0012. In addition, the results for K = 0.07 show that the lift and drag coefficients at a maximum angle of attack are close to their static values for the discussed amplitudes and wing geometries.

This study experimentally determined the flapping dynamics of dual self-oscillating inverted flags placed inside turbulent channel flows in side-by-side and staggered configurations and their ability to enhance wall heat removal. Three clearance-distance to channel-width ratios (Gc/W = 0.19, 0.31, and 0.5) and three streamwise-distance to channel-width ratios (Gy/W = 0, 2, and 4) were used to examine distinct flag behaviors. A single flag mounted to the heated wall with various gap clearances was chosen as the benchmark. The flags’ time-varying motions were recorded by a high-speed camera system. Three dynamic regimes were identified on the basis of the flags’ dimensionless stiffness and the channel flow’s Reynolds number: the biased mode, the flapping mode, and the deflected mode. Temperature sensitive paint (TSP) measurements demonstrated that the best cooling enhancement, with a local Nusselt number ratio of over 1.6, was achieved for the single flag system at Gc/W = 0.19. Adding another inverted flag to the side-by-side configuration at Gc/W = 0.19 further enhanced the heat removal performance on both channel walls, and the flapping period increased by nearly 50%. However, placing two side-by-side flags close to each other (Gc/W = 0.31) led to chaotic flapping motions, resulting in diminutive augmentation in heat transfer and an appreciable penalty in pressure drop. In the staggered configuration at Gy/W = 2 and 4, the two inverted flags synchronously flapped with a stable phase difference, and the flapping periods were similar to those of the single flag. The peak Nusselt number ratio was 1.9 for Gy/W = 2, which was attributed to the concerted influence of the staggered inverted flags. The system with staggered flags placed close to the heated wall had a higher thermal enhancement factor than the system with flags mounted in tandem along the channel centerline.

This paper examines the unsteady lift, drag and moment coefficients experienced by a thin airfoil in high-amplitude pitch ramp motion. Experiments have been carried out in a wind tunnel at moderate Reynolds number ($Re\approx 1.45\times 10^{4}$), using a rigid flat-plate model. Forces and moments have been measured for reduced pitch rates ranging from 0.01 to 0.18, four maximum pitch angles ($30^{\circ },45^{\circ },60^{\circ },90^{\circ }$) and different pivot axis locations between the leading and the trailing edge. Results confirm that for reduced pitch rates lower than 0.03, the unsteady aerodynamics is limited to a stall delay effect. For higher pitch rates, the unsteady response is dominated by a buildup of the circulation, which increases with the pitch rate and the absolute distance between the pivot axis and the $3/4$-chord location. This circulatory effect induces an overshoot in the normal force and moment coefficients, which is slightly reduced for a flat plate with a finite aspect ratio close to 8 in comparison with the two-dimensional configuration. A new time-dependent model has been tested for both the normal force and moment coefficients. It is mainly based on the superposition of step responses, using the Wagner function and a time-varying input that accounts for the nonlinear variation of the steady aerodynamics, the pivot point location and an additional circulation which depends on the pitch rate. When compared with experiments, it gives satisfactory results for $0^{\circ }$ to $90^{\circ }$ pitch ramp motion and captures the main effect of reduced pitch rate and pivot point location.

NaBr is considered as one of the typical low temperature salts employed for solid sorption refrigeration. The novel concept of solid sorption heat pipe (SSHP) which integrates heat and mass transfer with solid-gas sorption technology is expected to fulfill the continuous heat transfer and alleviate the drawbacks of both conventional heat pipe and thermosyphon. In this paper, an experimental system for both sorption/desorption unit and heat transfer unit is designed and the experiments of non-equilibrium sorption/desorption performances of NaBr-NH3 and heat transfer performances of SSHP with different molar amounts and inclination angles are carried out, respectively. The test results of sorption/desorption unit demonstrate that the increase of desorption quantity becomes very slow when the heating temperature reaches up to 75 °C and above, and with the increase of condensing pressure, the mass of ammonia desorbed from the ammoniate NaBr becomes less. The investigations of SSHP with 3 mol sorbates show that the heat transfer quantity increases significantly with the heating temperature reaches to 55 °C and above, in which the relatively higher desorption rate can be obtained. The largest value of heat transfer quantity per unit molar ammonia for 3 mol sorbates is close to that of 5 mol under the condition of heating temperature of 90 °C and cooling temperature of 20 °C. When the angle of inclination changes from 90° to 45°, the heat transfer capacity of SSHP declines more significantly compared with that of the angle from 45° to 0°.

A novel pressure-sensitive paint (PSP) system has been developed which uses an embedded organic light-emitting diode (OLED) layer as excitation, and thus eliminates the usual requirement of an external light source. This system consists of an OLED layer, an optical filter layer and a polymer-ceramic (PC) PSP layer with fast response. The OLED provides green excitation light (around 500 nm) for PSP, while the optical filter and (550 nm short-pass) removes unwanted longer wavelength light to prevent possible interference with the PSP signal. A PC-PSP layer is applied on top of the filter with well-controlled basecoat thickness (~ 10 μm) to allow sufficient light transmittance. It is also important that the OLED is modulated with a limited duty cycle and synchronized with the camera exposure to minimize uncertainties mostly due to the inherent heating effect of OLED. This OLED-based PSP has a pressure sensitivity comparable to the regular PC-PSP, and it is well-suited for pressure measurements on moving surfaces since its illumination field is independent of the model motion. Its advantage over a conventional PSP system was demonstrated through applications on a flapping plate under the impingement of a nitrogen jet.

In order to obtain the pulse contour with high signal to noise ratio in short observation time, a denoising method of pulsar photon signal based on recurrent neural network is proposed, and the actual observation data of Rossi satellite in the United States are used to analyze and verify the method. Using signal to noise ratio and mean square variance as the evaluation index, the results of measured data show that recurrent neural network has a significant effect on reducing the noise contained in the observational contour of pulsars. Compared with the traditional method of periodic folding, the proposed method can greatly reduce the observation time needed to obtain the contour of the same signal to noise ratio, and is more conducive to realtime application.

The pinned and clamped configurations of a single piezoelectric membrane placed in free stream flow were extensively compared in terms of energy harvesting performance and spatiotemporal variations in the membrane's displacement and curvature. The results convincingly show a considerable gain in the harvested energy of the pinned membrane due to the broad region with large curvature. The self-adaptive nature of the pinned membrane in response to different flow directions was also demonstrated. A comprehensive study at the reduced flow speed regime U* =22.8 to 38 was made of two parallel pinned membranes with different cross-flow separation distances ( D/L =0.6 to 2.2). The shapes of the two flapping membranes were visualized with a high-speed camera while the synchronous variation of the terminal load's voltage on each membrane was recorded. At small separation distance 0.6 ≤ D/L ≤ 0.8 , the membranes flapped with a phase difference of 0.5 π at U* =22.8 to 28.5; the increase in velocity resulted in a switch to the in-phase flapping mode. At D/L = 1.0 to 1.8, the two membranes flapped in the anti-phase mode for the entire velocity region U* = 22.8 to 38.0, along with a considerable gain in the harvested energy over the other coupled modes. The results indicated that a large region ( D/L =1.0–1.8, U* =22.8–38) with the anti-phase coupling in the D / L - U* plane was suitable for energy harvest. As the separation distance increases further to 2.0≤ D/L ≤ 2.2, the membranes flapped at different frequencies. Finally, the influence of the terminal load on the power was determined for the separation distance D/L =1.2; the anti-phase flapping membranes were connected into circuits with reversed electrode arrangements, reaching a peak power P =10.31 mW at the optimal terminal load for U* =36.1.

The flapping dynamics of a piezoelectric membrane placed behind a circular cylinder, which are closely related to its energy harvesting performance, were extensively studied near the critical regime by varying the distance between the cylinder and the membrane. A total of four configurations were used for the comparative study: the baseline configuration in the absence of the upstream circular cylinder, and three configurations with different distances ( S ) between the cylinder and the membrane ( S / D =0, 1, and 2). A polyvinylidene fluoride (PVDF) membrane was configured to flutter at its second mode in these experiments. The Reynolds number based on the membrane’s length was 6.35×10 4 to 1.28×10 5 , resulting in a full view of membrane dynamics in the subcritical, critical, and postcritical regimes. The membrane shape and the terminal voltage were simultaneously measured with a high-speed camera and an oscilloscope, respectively. The influence of the upstream cylinder on the membrane dynamics was discussed in terms of time-mean electricity, instantaneous variations and power spectra of terminal voltage and membrane shape, fluctuating voltage amplitude, and flapping frequency. The experimental results overwhelmingly demonstrated that the terminal voltage faithfully reflected various unsteady events embedded in the membrane’s flapping motion. For all configurations, dependency of the captured electricity on a flow speed beyond the critical status was found to follow the parabolic relationship. In the two configurations in which S / D =0 and 1, the extraneously induced excitation by the Karman vortex street behind the circular cylinder substantially reduced the critical flow speed, giving rise to effective energy capture at a lower flow speed and a relatively high gain in power output. However, in the configuration in which S / D =2, the intensified excitation by the Karman vortex street on the membrane considerably reduced the captured energy. Finally, a transient analysis of the membrane’s flapping dynamics in the configuration in which S / D =0 was performed in terms of phase-dependent variations of the membrane segment’s moving speed, membrane curvature, and terminal voltage; the analysis resulted in a full understanding of the energy harvesting process with consecutive inter transfer of elastic, kinetic, and electric energies.

International audience; The unsteady flow behind an inverted flag placed in a water channel and then excited into a self-oscillating state is measured using time-resolved particle image velocimetry. The dynamically deformed profiles of the inverted flag are determined by a novel algorithm that combines morphological image processing and principle component analysis. Three modes are discovered with the successive decrease in the dimensionless bending stiffness: the biased mode, the flapping mode, and the deflected mode. The distinctly different flow behavior is discussed in terms of instantaneous velocity field, phase-averaged vorticity field, time-mean flow field, and turbulent kinetic energy. The results demonstrated that the biased mode generated abundant vortices at the oscillating side of the inverted flag. In the deflected mode, the inverted flag is highly deflected to one side of the channel and remains almost stationary, inducing two stable recirculation zones and a considerably inversed flow between them. In the flapping mode, the strongly oscillating flag periodically provides a strengthened influence on the fluid near the two sidewalls. The reverse von Kármán vortex street is well formed and energetic in the wake, and a series of high-speed impingement jets between the neighboring vortices are directed toward the sidewalls in a staggered fashion.

Fast-responding pressure-sensitive paint (Fast PSP) and temperature-sensitive paint (TSP) measurements were conducted on two turbocharger compressors using a single-shot lifetime-based technique. The fast PSP and TSP were applied on separate blades of one compressor, and both paints were excited by a pulsed 532 nm Nd:YAG laser. The luminescent decay signals following the laser pulse were recorded by a CCD camera in a double-exposure mode. Instantaneous pressure and temperature fields on compressor blades were obtained simultaneously, for rotation speeds up to 150,000 rpm. The variations in pressure and temperature fields with rotation speed, flow rate and runtime were clearly visualized, showing the advantage of high spatial resolution. Severe image blurring problems and significant temperature-induced errors in the PSP results were found at high rotation speeds. The first issue was addressed by incorporating a deconvolution-based deblurring algorithm to recover the clear image from the blurred image using the combination of luminescent lifetime and rotation speed. The second issue was resolved by applying a pixel-by-pixel temperature correction based on the TSP results. The current technique has shown great capabilities in flow diagnostics of turbomachinery and can serve as a powerful tool for CFD validations and design optimizations.

Heat transfer enhancement by tandem self-oscillating inverted flags was investigated for channel flow. An isolated flag was selected as the benchmark. The highly unsteady flapping motion of the inverted flag was captured using a high-speed camera and identified by the structure boundary detection algorithm. The resultant temperature fields were determined by temperature sensitive paint measurement. Three dynamic regimes were observed for the isolated inverted flag: biased, flapping, and deflected modes. The results show that the self-oscillating inverted flag in the flapping mode exhibited the most energetic motion, with a maximum amplitude of 1.75 times of the flag length and a Strouhal number 0.17. This significantly promoted heat removal from the heated wall, with a considerable local Nusselt number ratio exceeding 1.5. Tandem flags flapped synchronously with the same frequency at a low Reynolds number and a close distance G* between two inverted flags, and the phase difference depended linearly on the separation distance. Increases in the separation distance and Reynolds number led to decoupling behavior. Local Nusselt number ratio peak regions were found behind both the front and rear flags, and the heat transfer performance behind the rear flag was superior to that behind the front flag. The global Nusselt number ratio was not sensitive to the separation distance and Reynolds number for tandem flag configurations. Increasing Reynolds number reduced the mechanical loss, so operating the tandem inverted flags’ system at a high Reynolds number moderately improved the heat transfer efficiency.

The influence of an inverted flag’s length-to-channel-width ratio (C* = L/W) on its oscillating behavior in a channel flow and the resultant vortex dynamics and heat transfer are determined experimentally. Three systems with C* values of 0.125, 0.250, and 0.375 were chosen for comparison. The interaction of highly unsteady flow with the inverted flag is measured with time-resolved particle image velocimetry. Variations in the underlying flow physics are discussed in terms of the statistical flow quantities, flag displacement, phase-averaged flow field, and vortex dynamics. The results show that the increase in C* shifts the occurrence of the flapping regime at high dimensionless bending stiffness. With the flag in the flapping region, three distinct vortex dynamics—the von Karman vortex street, the G mode, and the singular mode—are identified at C* values of 0.375, 0.250, and 0.125, respectively. Finally, the heat transfer enhancement from the self-oscillating inverted flag is measured to serve as complem...

A series of carboxylic acid functionalized hybrid linear-dendritic block copolymers (LDBCs) derived from methoxy poly(ethylene glycol) (MPEG) and variant generation dendrons from 2,2-bis(hydroxymethyl) propionic acid were synthesized and employed as CaCO3 crystallization growth modifiers. Mainly spherical vaterite particles of gradually reduced sizes were produced with the increase of the polymer additive concentration and/or the dendron segment generation number, while the incorporated polymer organic components in the particles increased for the promoted binding efficiency and ever enhanced adsorption ability. A higher mineralization temperature resulted in significantly larger particle size and partly calcite formation. Under the same molar concentration of carboxylic acid, the same size level particles were obtained which manifested the crucial role of the functional group, meanwhile, the slight decrease of the spherical vaterite diameters with increasing generation number and especially the formation of particular pine-cone shaped calcite crystals also revealed the significant effect of the architectural structure of variant generations and some special characters of the hybrid LDBC structures.

The environmental impact of construction process is closely related to the operational resource arrangement of the construction scheme. At the viewpoint of green construction, this research focuses on the onsite construction phase from the preparation to the completion and acceptance. From the perspective of ecological economics, based on emergy theory and its methodology, a comprehensive analysis on the flows of the input-output capital, energy and material is done to the construction operational resources, i.e., manpower, material, and equipment. A framework of emergy analysis is setup connecting ecological and economical system of construction process. This research has theoretical and practical reference for the innovation of rethinking construction operational resources with the sense of green construction.

Urban land price is a significant index of the social-economic development. It's very important to establish scientific and appropriate mathematic prediction model to forecast its change trend. The methods of Conventional prediction including trend line, Grey model and so on. For the systems with apparent fluctuation, such as the land price prediction, the precision of prediction is lower. However, Markov model could solve the problem of randomness and great changed data which is based on the stability ineffectiveness theory. So, we combine the two models and build the Grey-Markov prediction model to forecast the urban land price of Tangshan city. The conclusion reveals that the new model has higher accuracy in prediction of urban land price. But there is also some limitation in different conditions and it should be improved by more research.