Ratio Of Cavity Length Research Articles

Laser-induced micro-cavity on a fiber end with a harmonic-Vernier effect for salinity sensing

In this paper, a fiber optic salinity sensor based on Fabry–Perot interference (FPI) with a harmonic-Vernier effect is suggested. An open cavity and a resin solid cavity are grown at the end of the fiber by a unique fiber-end photopolymerization and integration (FEPI) technique. When seawater fills the open cavity, it changes the optical path length (OPL) of the interferometer directly. While the OPL of the reference interferometer is hardly impacted by the seawater. The insertion of the harmonic envelope shifts greatly with salinity. Tunable sensing performances are achieved by adjusting the cavity length ratio(CLR) according to a theoretical model. The maximum sensitivity of 6.53 nm/‰is attained in the range of 25 ‰to 45 ‰when its CLR approaches 1.18. In addition, the measuring accuracy, consistency, and temperature compensation method are also experimentally investigated. The suggested sensor is a prospective competitor in the field of measuring the salinity of seawater due to the advantages of high sensitivity, compact size, large dynamic range, and adjustable capabilities.

Research on the Influence of Characteristics of the Annular Connecting Pipe on the Transmission Loss of the Expanded Exhaust Muffler

In order to broaden the muffler frequency band in the low-frequency range of the exhaust muffler and to achieve the purpose of broadband noise reduction, in this paper, a model of an annular connecting pipe muffler is proposed using the finite element method (FEM) to simulate the nonreflection boundary condition and to solve the transmission loss (TL). In addition, the experimental value is obtained by the spatial five-point measurement method and compared with the simulated value, and the validity and reliability of the solution model are verified. Compared with a simple expansion muffler, the average TL of the annular connecting pipe muffler is increased by 11.86 dB, and the maximum TL is increased by 18.31 dB, effectively widening the muffler frequency area, and the overall performance is effectively improved. Finally, the influence of structural factors is analyzed, including the width (W) of the annular connecting pipe, the length (L) of the annular connecting pipe, and the length ratio (m) of the front and rear chambers on the TL and on the width of the anechoic frequency band. The results reveal that the width and length of the annular connecting pipe and front-to-back cavity length ratio are the most significant factors to influence the TL, muffler frequency band, and elimination or reduction of the passing frequency, respectively.

Study of the Jet Output Characteristics under Multi−Source Coupling

The challenges posed by elevated rock hardness, deficient drillability, excessive friction torque, and significant underpressure in extended−reach horizontal wells are the primary factors that contribute to low ROP (Rate of Penetration) and limited horizontal reach during the drilling operation. Reducing drag and friction is one of the primary methods of addressing the aforementioned challenges. To augment the pulse output characteristics of the oscillating jet and bolster the energy of the hydrodynamic impact load, we developed and designed a multi−source impact oscillation speed−increasing tool coupled with blade rotation disturbance and multi−order oscillation cavity self−excitation. We utilized fluid dynamics software to model and conduct numerical analysis on the multi−source pulsed jet generator. Furthermore, we constructed a prototype and subjected it to testing. This paper examines the impact of dimensionless structural parameters on the pressure output characteristics of the multi−source pulse−jet generator. Specifically, we used three dimensionless quantities (cavity length ratios, cavity diameter ratios, and inner wall collision angle ratios) to study this effect. The findings indicate that the multi−source impact oscillation speed−increasing tool is capable of augmenting the pulse oscillation amplitude, and the frequency of pulse oscillation can be adjusted within the range of 5 Hz to 15 Hz. During the study, we determined that the optimal oscillation output characteristics can be achieved when the cavity diameter ratio is 0.8, the cavity length ratio is 1.0, and the inner wall collision angle ratio is 1.5. These findings present a novel approach for the development of downhole hydraulic impact oscillation speed−increasing tools.

NUMERICAL INVESTIGATION OF RECTANGULAR RIB ROUGHNESS EFFECTS ON FLOW RESISTANCE IN OPEN-CHANNEL FLOW

A series of numerical simulations are undertaken to investigate the flow resistance of a rough open-channel flow. The roughness is generated by periodically spaced bars and transversely glued on the channel bottom. The free surface flow is modeled by using the finite volume method and the Reynolds stress model coupled to the two-phase model. The results obtained show that for a given bar thickness, the maximum flow resistance is obtained when the ratio of cavity length to roughness height is around 12.5. For several longitudinal thicknesses of the bars, it is found that the flow resistance and the generated roughness are higher when the longitudinal thickness-to-height ratio of the bars is less than unity. For given streamwise spacing bars, the friction factor and the generated roughness are inversely proportional to the longitudinal thickness of the bars. By including the geometric dimensions of the roughness elements and their spacing, a relationship between the friction factor and the generated roughness is derived. A good agreement was found with the existing expressions in the relevant literature. It is postulated that the extension of the proposed formula to the large-scale roughness reproduces acceptable results.

Динамика конвективной системы с плавающим протяженным теплоизолятором

The paper presents an experimental study of a convective flow in a rectangular cell of length L, width W and depth H, filled with water, heated from the bottom and cooled from the top, with a heat-insulating disk floating at a fixed height h (the disk diameter is slightly smaller than the cavity width). Such a system exhibits a range of modes, including periodic movements of the float along the cavity, chaotic motions of various types, and drift of the disk to the edge of the cavity without further movements. In addition to the Rayleigh, Prandtl numbers and the cavity dimension ratio (L/H), usual for convective systems, the structure of convective flows in the cavity depends on geometric parameters associated with the floating disk: the relative height of the body position (h/H) and the body size to the cavity length ratio (D/L). Experiments were performed for fixed W=100mm, H=40mm, D=98mm, and h=4mm, but different lengths 170mm < L < 500mm. It is shown that periodic motions occur only in a limited range of the body size to the cavity size ratio. As the length of the cavity increases, a chaotic mode of intermittent motion of the disc occurs; at the maximum cavity length considered, the disk is shifted to the extreme position and remains there. The structure of the convective flow at different phases of periodic motions has been reconstructed by PIV (particle image velocimetry) technique.

Study on the influence of structure factors of diesel engine exhaust purification muffler on transmission loss in different frequency bands

The main purpose of exhaust mufflers design is to improve the TL (transmission loss) of the target frequency band. Therefore, this paper first proposed an exhaust muffler model with foam ceramics as sound-absorbing material for a diesel engine. The finite element AML (Automatic Matched Layer) method is used to simulate the non-reflective boundary conditions and calculate the TL. In addition, the validity and reliability of the solution model are verified by comparing the experimental value and simulation value of the TL. Compared with the prototype muffler, the TL of the exhaust purification muffler has increased by an average of 6.96 dB in the frequency range of 20–4500 Hz. Finally, the influence law of structure factors m (expansion ratio), n (cavity-length ratio) and p (length-diameter ratio) on TL in different frequency bands shows that: when changing the structure factors to increase the TL value of the exhaust purification muffler, the expansion ratio should be prioritized in the low-medium frequency bands, the cavity-length ratio should be prioritized in the medium–high frequency bands, the length-diameter ratio should be prioritized in the high frequency bands.

MHD mixed convection of localized heat source/sink in an Al2O3-Cu/water hybrid nanofluid in L-shaped cavity

The effect of source/sink heat location and size on Magneto-hydrodynamic mixed convection in hybrid nanofluid of Al2O3-Cu/Water within the L-shaped cavity is studied in this paper. Two uniform heat sources are put at the corners of the bottom walls of enclosure and the beginning and the end of L-shape enclosure set to be at the cold temperature. The other parts of enclosure’s walls are supposed to be insulated. The finite difference method and Boussinesq approximation is utilized to discrete the governing equations. The fundamental flow physics and thermal behavior are explored in terms of pertinent parameters such as the effects of sink/source heat generation, magnetic field and angle, Hartmann number, cavity length ratio, and hybrid volume fraction on average and surface Nusselt number, streamlines, isotherms, and entropy generation are studied. The results demonstrate that maximum amount of the sink power causes the best heat transfer performance.

Fin performance of 3-D aerator devices with backward lateral deflectors

In the present work, a 3-D aerator device with backward lateral deflectors, called BLD-3-D aerator device, is developed, and the lateral cavity and fin performance of the BLD-3-D aerator device are experimentally investigated. The findings show that, the relative lateral cavity length with backward lateral deflectors is shorter than that with current lateral deflectors under the same approach flow conditions, and on the basis of the results of the relative cavity length ratio between the lateral and bottom aerators the BLD-3-D aerator device is of remarkable performance for the water fin control thanks to the decrease of the relative lateral cavity length.

Computational fluid dynamics simulations of the flow field characteristics in a novel exhaust purification muffler of diesel engine

The purpose of this paper is to improve the emission performance of diesel engines. A novel exhaust purification muffler was proposed and designed. The flow field characteristics of the exhaust purification muffler were studied based on the finite volume method, the pressure loss of the exhaust purification muffler was 3315 Pa, and the pressure loss of the exhaust purification muffler was just 2% higher than the original muffler. Then, a three-dimensional numerical simulation model was established and used to investigate the effect of different expansion ratio, cavity length ratio, and ratio of length to diameter on the flow field characteristics in an exhaust purification muffler of diesel engine. The study was shown that the porous media (ceramic foam) had a great influence on the flow field distribution, where the air flow velocity was stable and the pressure distribution was trapezoidal, having a good pressure reduction and deceleration effect. With the increase of the expansion ratio parameter, the airflow cross-section area changed when air entered into the inlet silencing cavity, which had great influence on the velocity field and the pressure loss. Because of the improvement of cavity length ratio parameter, the flowing distance in the inlet silencing increased, which caused more local turbulence and pressure fluctuation. Also with the increase of the ratio of length to diameter parameter, the volume of inlet silencing chamber and the air flow space increased. The change of the structural parameters of each scheme had a certain influence on the pressure loss. The maximum pressure loss changing value among the expansion ratio schemes was 878 Pa, then the maximum pressure loss changing value among the cavity length ratio schemes was 328 Pa, and it was 89 Pa among the cavity length ratio schemes. The pressure loss caused by the expansion ratio parameter changed greatly, and the pressure loss changing value caused by the change of the cavity length ratio parameter and the ratio of length to diameter parameter was relatively small. In this paper, a muffler which contained a ceramic foam and had the functions of exhaust soot purification and noise elimination was supplied. The effects of the structure factors on flow field characteristics were studied. The guidance for the design and improvement of muffler is able to be supplied in this paper.

Two-dimensional analysis of low-pressure flows in an inclined square cavity with two fins attached to the hot wall

The gaseous low-pressure flow of a steady-state two-dimensional laminar natural convection heat transfer in a cavity with an attached two solid fins to the hot wall is numerically investigated. Such flows can be found in many engineering applications such as the “evacuated” solar collectors and in the receivers of the solar Parabolic Trough Collectors (PTCs), nuclear reactor cooling and electronic equipment cooling. Buoyancy effect is modeled using Boussinesq approximation. Effects of Knudsen and Rayleigh numbers, location and length of the fins, conductivity ratio and fins porosity, and the tilt angle on the flow and heat transfer characteristics are investigated. Physical parameters ranges in this study are as follows; 0≤Kn≤0.1, 103≤Ra≤106, LF takes the values of 0.25, 0.5 and 0.75 m, HF takes the values of 0.25_0.5, 0.25_0.75 and 0.5_0.75, 1≤Kr≤8000, 0≤ε≤1 and 0∘≤θ≤90∘. It is shown that Nusselt number depends directly on Rayleigh number and inversely on Knudsen number. In addition, it is found that attaching two solid fins to the hot wall will enhance the heat transfer for such flows. Moreover, it is found that the porous fins are superior to the solid fins as far as the heat transfer is concerned. In addition, it is shown that for the geometry where the lower fin height to cavity length ratio is 0.25 and the upper fin height to cavity length ratio is 0.75, the best heat transfer is achieved. In addition, for the fin lengths considered in the study, it is concluded that by increasing the length of the fin, a better heat transfer is achieved. Also, it is found that by increasing the tilt angle of the cavity, a better heat transfer is achieved up to a certain value which was found to be (30°) where beyond this value, Nusselt number will decrease. In addition, it is found that by increasing the conductivity ratio up to a certain value (103), better heat transfer is gained. Finally, a correlation among Nusselt number and the parameters investigated in this research proposed as Nu=0.02197ε0.00932sin(θ)0.00373Kr0.0273(h2/LF)2.814Ra0.13((h2−h1)/LF)1.373(h1/LF)1.615Kn0.37.

Scale effects on the performance of sawtooth spoilers in transonic rectangular cavity flow

An experimental study was conducted on the effectiveness of sawtooth spoilers at suppressing acoustic tones within a rectangular cavity with a length-to-depth ratio of five and a width-to-depth ratio of two, operating at a freestream Mach number of 0.71. Whereas previous research has focussed on the ratio of spoiler height to boundary-layer thickness (h/δ), this study also considers the effect of the ratio of cavity length to boundary-layer thickness (L/δ). Using a combination of unsteady pressure measurements and particle image velocimetry, it was established that consideration of the magnitude of both parameters is important when designing passive control methods for transonic cavities. A correlation was developed which suggests that in order to suppress fully the cavity tones, a critical spoiler height, hcr, is defined such that hcr/δ = 0.065 ≤ L/δ ≤ 0.082.

Analytical and experimental investigations of the pulsed air–water jet

This paper describes a new way of generating pulsed air–water jet by entraining and mixing air into the cavity of a pulsed water jet nozzle. Based on the theory of hydro-acoustics and fluid dynamics, a theoretical model which describes the frequency characteristic of the pulsed air–water jet is outlined aimed at gaining a better understanding of this nozzle for generating pulses. The calculated result indicates that as the air hold-up increases, the jet oscillation frequency has an abrupt decrease firstly, and then reaches a minimum gradually at α (air hold-up)=0.5, finally it gets increased slightly. Furthermore, a vibration test was conducted to validate the present theoretical result. By this way, the jet oscillation frequency can be obtained by analyzing the vibration acceleration of the equal strength beam affected by the jet impinging. Thereby, it is found that the experimental result shows similar trend with the prediction of the present model. Also, the relationship between vibration acceleration and cavity length for the pulsed water jet follows a similar tendency in accord with the pulsed air–water jet, i.e. there exists a maximum for each curve and the maximum occurs at the ratio of L/d1 (the ratio of cavity length and upstream nozzle diameter) =2.5 and 2.2, respectively. In addition, experimental results on specimens impinged by the pulsed water jet and pulsed air–water jet show that the erosion depth increases slightly with air addition within a certain range of cavity length. Further, this behavior is very close to the vibration test results. As for erosion volume, the air entrained into the cavity significantly affects the material removal rate.

Experimental Study of Supersonic Entrainment Using a Cavity

The effect of wall-mounted three-dimensional cavities on the entrainment of gaseous injectant into a supersonic stream of Mach number 1.7 is studied. Entrainment induced by flow unsteadiness, turbulence, and exchange of fluid between the cavity and mainstream flow has been investigated. To clarify the influence of the ratio of cavity length to width on the fluid dynamic behavior, cavities of ratios between two and four were applied at a constant length-to-depth ratio . Acoustic oscillations generated from the cavity were observed to have profound impact on mass exchange between the cavity and the freestream flow. These acoustic oscillations were in turn found to be dependent on the ratio of the cavity. Shift in dominant acoustic mode was observed as the ratio was changed from three to four. Spillage of the shear layer over the cavity walls and turbulence induced in the cavity were probed by measuring velocity using laser Doppler velocimetry. Entrainment of secondary gaseous injection into the main flow from the cavity was also observed to depend on the cavity ratio.

Refractive index sensing characteristic of a hybrid-Fabry-Pérot interferometer based on an in-fiber ellipsoidal cavity

A hybrid-Fabry-Perot (F-P) interferometer based on an in-fiber ellipsoidal cavity is presented, and the refractive index sensing properties are studied. The ellipsoidal air-microcavity is formed by splicing together a single-mode fiber and a photonic crystal fiber with special arc-discharge technique. The cavity loss is analyzed by using a Gaussian beam model and the ABCD law, and the physical model of electromagnetic transmission is established. According to the cavity length ratio, there are two kinds of the influences of environment refractive index on interference fringe: contrast modulation and wavelength modulation. A fiber refractive index sensor with an enclosed air cavity based on wavelength demodulation is proposed in this paper. The result of simulation shows that the sensors has no turning point in a range of 1-1.6. A wavelength interrogation technique is used to demodulate refractive-index with high sensitivity (～ 37.088 nm·RIU-1) and high resolution (～ 2.69× 10-5) and with low temperature crosstalk. Experimental results are in good agreement with the theoretical ones. The F-P fiber sensor also holds advantages such as compactness, low cost, easy fabrication, high contrast, high resolution, no turning point, and low temperature crosstalk.

Three-dimensional flow within shallow, narrow cavities

AbstractThe three-dimensional structure of incompressible flow in a narrow, open rectangular cavity in a flat plate was investigated with a focus on the flow topology of the time-averaged flow. The ratio of cavity length (in the direction of the flow) to width to depth was $l{: }w{: }d= 6{: }2{: }1$. Experimental surface pressure data (in air) and particle image velocimetry data (in water) were obtained at low speed with free-stream Reynolds numbers of ${\mathit{Re}}_{l} = 3. 4\times 1{0}^{5} $ in air and ${\mathit{Re}}_{l} = 4. 3\times 1{0}^{4} $ in water. The experimental results show that the three-dimensional cavity flow is of the ‘open’ type, with an overall flow structure that bears some similarity to the structure observed in nominally two-dimensional cavities, but with a high degree of three-dimensionality both in the flow near the walls and in the unsteady behaviour. The defining features of an open-type cavity flow include a shear layer that traverses the entire cavity opening ultimately impinging on the back surface of the cavity, and a large recirculation zone within the cavity itself. Other flow features that have been identified in the current study include two vortices at the back of the cavity, of which one is barely visible, a weak vortex at the front of the cavity, and a pair of counter-rotating streamwise vortices along the sides of the cavity near the cavity opening. These vortices are generally symmetric about the cavity centre-plane. However, the discovery of a single tornado vortex, located near the cavity centreline at the front of the cavity, indicated that the flow within the cavity is asymmetric. It is postulated that the observed asymmetry in the time-averaged flow field is due to the asymmetry in the instantaneous flow field, which switches between two extremes at large time scales.

The modeling of end pumping Yb3+:YVO4 quasi-three-level laser

In a Yb3+ laser, the two-energy level structure is close to the quasi-three-level model, but different from that for the Nd and Tm lasers, so it is necessary to investigate the quasi-three-level modeling that will be applied to the Yb3+ laser. Based on the energy level structure, cavity gain and loss as well as population distribution, we present the modeling. Introducing an effective cavity length factor, the laser intensity is calculated and the threshold is obtained. Comparison with the experiments, indicates that the effective cavity length ratio changes the fractional population function and loss, which would influence the threshold and output in turn. Applied to investigate the laser property in the process of end pumping Yb3+:YVO4 laser, we get the threshold being 1.1 W, corresponding to the L=1 mm and T=1%; whereas the threshold is 3.9 W, corresponding to the L=2 mm and T=10%.

Extracting the external-cavity key of a chaotic semiconductor laser with double optical feedback by spectrum analyzer

Optical-feedback laser diodes have been widely applied in chaotic optical communication, because it can simply generate wideband and high-dimension chaos and its external-cavity length is often regarded as an additional key. In this paper, it is experimentally demonstrated that the time delay signature of a chaotic laser diode with optical feedback can be identificated. Through locally enlarging the power spectral of chaotic light and observing its fine structure, the external-cavity key can be directly extracted by the spectrum analyzer, regardless of the laser diode with single or dual optical feedback of different external cavity length ratio.

Cavity length resonances in a nanosecond singly resonant optical parametric oscillator

Resonant output energy enhancement in a singly resonant nondegenerate type-I optical parametric oscillator with a volume Bragg grating output coupler is demonstrated. The resonances occur when the pump laser and parametric oscillator cavity length ratio is an integer or a fraction of small integers. Although the length resonances are similar to those observed in doubly resonant optical parametric oscillators, the physical mechanism is distinctly different. The resonances in the singly resonant oscillator are caused by correlation of the instantaneous power between the quasi-periodic multimode pump laser beam and the OPO signal.

Large-scale structures of turbulent flows over an open cavity

Abstract Low Mach number turbulent flows over an open cavity were studied to investigate the quantitative characteristics of large-scale vortical structures responsible for self-sustained oscillations. Wind tunnel experiments with particle image velocimetry (PIV) were conducted in the range of the ratio of cavity length (L) to depth (D), 1

Estimation of Cavity Length in EHL Rolling Point Contact

Reciprocating lubricated contacts sometimes suffer from oil starvation due to cavitation at the reversal of motion. However, the behavior of cavities is not well understood such that starvation can be theoretically predicted. In this study, the length of cavity in a steady state elastohydrodynamic lubricated point contact was calculated. For numerical simulation, a modified Elrod algorithm was used. An equation was obtained for the cavity enclosed in the oil meniscus. The equation was constructed with Moes dimensionless parameters M and L, assumed pressure of cavity, and viscosity pressure index of the lubricant. The dimensionless cavity length (or the ratio of cavity length by Hertzian contact radius) is proportional to the product of M−a and Lb. Careful examination of the equation elucidated that the cavity length is dominated by the viscosity, sum velocity, cavity pressure, and geometry of the contact. Experimental measurements with a ball-on-disk apparatus have shown good agreement. The validity of the equation suggests that the algorithm is applicable for complete transient simulations. In practice, the estimated cavity length can be a parameter for starvation.