Front Cavity Research Articles

Computer-aided design and calculation of the blade front cavity cooling system of the gas turbine engine

Computer-aided design and calculation of the blade front cavity cooling system of the gas turbine engine

A computational investigation of airfoil aeroacoustics for structural health monitoring of wind turbine blades

AbstractA generalized computational methodology for reduced order acoustic‐structural coupled modeling of the aeroacoustics of a wind turbine blade is presented. This methodology is used to investigate the acoustic pressure distribution in and around airfoils to guide the development of a passive damage detection approach for structural health monitoring of wind turbine blades for the first time. The output of a k − ε turbulence model computational fluid dynamics simulation is used to calculate simple acoustic sources on the basis of model tuning with published experimental data. The methodology is then applied to a computational case study of a 0.3048‐m chord NACA 0012 airfoil with two internal cavities, each with a microphone placed along the shear web. Five damage locations and four damage sizes are studied and compared with the healthy baseline case for three strategically selected acoustic frequencies: 1, 5, and 10 kHz. In 22 of the 36 cases in which the front cavity is damaged, the front cavity microphone measures an increase in sound pressure level (SPL) above 3 dB, while rear cavity damage only results in six out of 24 cases with a 3‐dB increase in the rear cavity. The 1‐ and 5‐kHz cases show a more consistent increase in SPL than the 10‐kHz case, illustrating the spectral dependency of the model. The case study shows how passive acoustic detection could be used to identify blade damage, while providing a template for application of the methodology to investigate the feasibility of passive detection for any specific turbine blade.

Conjugate Heat Transfer Investigation on Swirl-Film Cooling at the Leading Edge of a Gas Turbine Vane

Numerical calculation of conjugate heat transfer was carried out to study the effect of combined film and swirl cooling at the leading edge of a gas turbine vane with a cooling chamber inside. Two cooling chambers (C1 and C2 cases) were specially designed to generate swirl in the chamber, which could enhance overall cooling effectiveness at the leading edge. A simple cooling chamber (C0 case) was designed as a baseline. The effects of different cooling chambers were studied. Compared with the C0 case, the cooling chamber in the C1 case consists of a front cavity and a back cavity and two cavities are connected by a passage on the pressure side to improve the overall cooling effectiveness of the vane. The area-averaged overall cooling effectiveness of the leading edge () was improved by approximately 57%. Based on the C1 case, the passage along the vane was divided into nine segments in the C2 case to enhance the cooling effectiveness at the leading edge, and was enhanced by 75% compared with that in the C0 case. Additionally, the cooling efficiency on the pressure side was improved significantly by using swirl-cooling chambers. Pressure loss in the C2 and C1 cases was larger than that in the C0 case.

Numerical study of effect of front cavity on hydrogen/air premixed combustion in a micro-combustion chamber

The micro-combustion chamber is the key component for micro-TPV systems. To improve the combustor wall temperature level and its uniformity and efficiency an improved flat micro-combustor with a front cavity is built, and the combustion performance of the original and improved combustors of premixed H2/air flames under various inlet velocities and equivalence ratios is numerically investigated. The effects of the front cavity height and length on the outer wall temperature and efficiency are also discussed. The front cavity significantly improves the average outer wall temperature, outer wall temperature uniformity, and combustion efficiency of the micro-combustor, increases the area of the high temperature zone, and enhances the heat transfer between the burned blends and inner walls. The micro-combustor with the front cavity length of 2.0 mm and height of 0.5 mm is suitable for micro-TPV system application due to the relatively high outer wall temperature, combustion efficiency, and the most uniform outer wall temperature.

MICROPHONE FRONT CAVITY DEPTH MEASUREMENT USING NON-CONTACT METHOD AT NATIONAL MEASUREMENT STANDARDS – NATIONAL STANDARDIZATION AGENCY OF INDONESIA

<p>Front cavity depth of microphone has influence in the determination of laboratory standard microphone sensitivity. Therefore this parameter is included in the measurement uncertainty budget. To determine microphone sensitivity accurately, it is necessary to measure the actual front cavity depth instead of using nominal value. This paper explains the measurement of LS1P and LS2P standard microphone front cavity depth using optical depth measurement facilities at SNSU-BSN and its effect on determining microphone sensitivity. The measurement was obtained from 4 positions distributed over the diaphragm for each microphone. The front cavity depth measurement result for LS1P is 1,94 mm ± 0,01 mm and for LS2P is 0,48 mm ± 0,01 mm These results comply with IEC 61094 Measurement Microphones-Part 2: Primary Method for Pressure Calibration of Laboratory Standard Microphones by Reciprocity Technique as the results are within the permissible range.</p>

Investigations on the Sealing Effectiveness and Unsteady Flow Field of 1.5-Stage Turbine Rim Seal

This paper presents a numerical investigation on the sealing effectiveness and unsteady flow field of a 1.5-stage turbine with the front and aft wheel-space cavities. The sealing effectiveness and flow structure are studied by solving three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) equations and shear stress transfer (SST) turbulence model. The numerical pressure and swirl ratio distributions in cavities with two computational models are compared with experimental data to determine the position of stationary/rotating domain interface. The time-averaged mainstream pressure distribution and sealing effectiveness of the rim seal at the front and aft cavities are studied by the steady and unsteady calculations. The unsteady results agree well with experimental data by comparison of the steady calculations. The effects of coolant flow rates on the sealing effectiveness and the flow field of the rim seal at the front and aft cavities are investigated. The obtained results show that the sealing effectiveness of the rim seal at the aft cavity is much larger than that of the rim seal at the front cavity at the same coolant flow rate. The less mainstream pressure fluctuation near the aft rim seal clearance and the clockwise vortex due to the pumping effect in the aft rim seal leads to this result. The mainstream pressure fluctuation downstream of the blade and the sealing effectiveness of the rim seal at the aft cavity under five operating conditions are computed. It shows that the square root of the mainstream pressure fluctuation amplitude downstream of the blade is proportional to the mainstream flow rate. The increase of the mainstream flow results in gradual decrease of the sealing effectiveness of the rim seal at the aft cavity.

High-output-power and high-temperature operation of blue GaN-based vertical-cavity surface-emitting laser

High output power values of 15.7 mW at 20 °C and 2.7 mW at 110 °C were obtained from a blue GaN-based vertical-cavity surface-emitting laser (VCSEL) under continuous-wave operation as a result of introducing a long-cavity (10λ) structure. The threshold current and voltage at 20 °C were 4.5 mA and 5.1 V, respectively. Owing to the reduced thermal resistance provided by the long-cavity structure and the adjusted reflectivity of the front cavity mirror, this VCSEL also exhibited a high slope efficiency of 0.87 W/A, a differential quantum efficiency of 31%, and a wall-plug efficiency of 8.9%.

Tongue position during speech as a function of palatal anatomy: Controls and glossectomy patients

This study examined the effect of palatal anatomy on tongue position during the complex speech movement seen in the motion from /ʃ/ to /l/ in “shell.” The study was interested in whether subjects with flatter/narrower palates would use more tongue anteriority than those with higher/wider palates. Anteriority is the percent of the tongue anterior to the first molar. Low palate speakers may use more anteriority due to less space in the palatal vault. The speech task “a shell” requires complicated deformation between the /ʃ/, which elevates the sides of the tongue, and the /l/, which lowers the sides, elevates the tongue tip, and retracts the root. In the past, palate effects have been shown to explain idiosyncratic subject differences. Palate height explained the use of apical vs laminal /s/. Palate width affected the anteriority of tongue position in cancer patients after glossectomy surgery. Therefore, this study examined 16 controls and 8 glossectomy patients. Initial measurements show more anteriority for patients than controls. In addition, patients with a large overbite (vertical overlap between upper and lower incisor) had more anteriority due to a smaller front cavity.

Experimental and numerical investigation on the pressure pulsation and instantaneous flow structure in a nuclear reactor coolant pump

Abstract The instantaneous vortical flow structure is one of the typical flow structures inside the nuclear reactor coolant pump (RCP), which would cause the unsteady pressure pulsations, vibrations of the unit and fatigue of components. Due to high safety requirement of the RCP during the actual operation of the nuclear power plants (NPPs), revealing instantaneous nature of vortical flow structure and its pressure pulsation becomes a crucial issue for studying the internal flow mechanism of the RCP. The purpose of this study is to shed comprehensive light on the pressure pulsation and instantaneous vortical flow structure in the RCP by using the experimental method and the numerical simulation method. Based on the result of comparison with the experiment and numerical simulation, it can be considered that the LES method can better identify instantaneous nature of vortical flow structures in the low frequency band. The instantaneous vortical flow structure is attached to the impeller RBPS (rotor blade pressure surface) and transient jet wake vortex flow structures between the impeller and diffuser under the rotor-stator interaction effect are fairly obvious by Q-criterion. On the other hand, in the axial-vorticity component distribution, the rotor-stator interaction effect between the impeller and diffuser cannot be clearly revealed. From the three-dimensional structures, the main vortex structures are in the front and back cavity of the right-hand side near the discharge nozzle and the right-hand side below the discharge nozzle in the spherical casing. Meanwhile, combined with pressure spectrum, it is convinced that their unsteady characteristic is the main reason that causes complex excitation frequencies in the low frequency band of the right-hand side near the discharge nozzle.

Numerical and theoretical investigation of the high-speed compressible supercavitating flows

The objective of this paper is to investigate the high-speed compressible supercavitating flows with numerical and theoretical methods. In the numerical simulation, calculations are performed by solving the Unsteady Reynolds-averaged Navier-Stokes (URANS) Equations using a cell-centered finite-volume method, and the k-ω SST turbulence model is applied as the closure model. Compressibility effects in liquid phase are modified by the equation of state (EOS), and vapor phase is treated as ideal gas. Firstly, the numerical results are validated with experiments conducted by Hrubes (2001). Results are shown for high-subsonic and transonic projectiles, there is a general agreement between the predicted cavity profiles and the experimental data. Secondly, the influence of the Mach number on the flow structure and cavitation dynamics from subsonic to supersonic flows is investigated. The results show that with the increase of Mach number, the radial dimension of the front cavity is reduced, which is caused by the dramatic increase of pressure around the projectile. An expression is proposed to analyze the flow parameters before and behind the shock wave based on the isentropic and potential assumption at the Mach number on the interval 1 ≤ Ma≤2.2. The relationship between pressure and density across the shock wave is also investigated. Overall, these findings are great interest in engineering applications.

Enhancement of slope efficiency and output power in GaN-based vertical-cavity surface-emitting lasers with a SiO2-buried lateral index guide

We have achieved a high output power of 6 mW from a 441 nm GaN-based vertical-cavity surface-emitting laser (VCSEL) under continuous wave (CW) operation, by reducing both the internal loss and the reflectivity of the front cavity mirror. A preliminary analysis of the internal loss revealed an enormously high transverse radiation loss in a conventional GaN-based VCSEL without lateral optical confinement (LOC). Introducing an LOC structure enhanced the slope efficiency by a factor of 4.7, with a further improvement to a factor of 6.7 upon reducing the front mirror reflectivity. The result was a slope efficiency of 0.87 W/A and an external differential quantum efficiency of 32% under pulsed operation. A flip-chip-bonded VCSEL also exhibited a high slope efficiency of 0.64 W/A and an external differential quantum efficiency of 23% for the front-side output under CW operation. The reflectivity of the cavity mirror was adjusted by varying the number of AlInN/GaN distributed Bragg reflector pairs from 46 to 42, corresponding to reflectivity values from 99.8% to 99.5%. These results demonstrate that a combination of internal loss reduction and cavity mirror control is a very effective way of obtaining a high output GaN-based VCSEL.

Frequency response simulation of the hybrid dual driver earphone using equivalent circuit model

By combining the multiple drivers into an insert earphone, the special filtering of hybrid dual drivers by earphone structure design can be applied to increase efficiency and the overall output level. In general, the back of the earphone structure lays a balanced armature driver for the mid to high frequency reproduction and a dynamic driver in front cavity creates deeper bass. For this distinctive structure of the earphone, this study proposed a frequency response simulation model using the equivalent circuit model. For the sound transmission between the two ports' structure, the correction factors for obtaining the transmitted impedance of special filter are proposed. The simulated responses shows that a good comparison between the measured result and the equivalent circuit simulation. As a result, the study has significant capacity to estimate the desired frequency response of a hybrid dual driver earphone.By combining the multiple drivers into an insert earphone, the special filtering of hybrid dual drivers by earphone structure design can be applied to increase efficiency and the overall output level. In general, the back of the earphone structure lays a balanced armature driver for the mid to high frequency reproduction and a dynamic driver in front cavity creates deeper bass. For this distinctive structure of the earphone, this study proposed a frequency response simulation model using the equivalent circuit model. For the sound transmission between the two ports' structure, the correction factors for obtaining the transmitted impedance of special filter are proposed. The simulated responses shows that a good comparison between the measured result and the equivalent circuit simulation. As a result, the study has significant capacity to estimate the desired frequency response of a hybrid dual driver earphone.

Numerical investigation of pressure distribution in a low specific speed centrifugal pump

To study the pressure distribution of the volute casing, front casing and back casing in a prototype centrifugal pump, the pressure experiments and numerical simulations are carried out at six working conditions in this paper. The experimental results shows that the asymmetry of static pressure distribution on volute casing and front cavity is caused by the tongue of the volute and it may result in high radial and axial resultant force which can cause vibration and noise in the centrifugal pump. With the increasing of flow rate, the asymmetry of static pressure distribution and the magnitude of static pressure values reduce. The numerical results indicate that the pressure fluctuation near the tongue is strongest and it becomes slighter at point away from the tongue. With the increasing of flow rate, the local high-pressure region in impeller passage reduces and the flow becomes smoother accordingly, whereas the fluid speed becomes much higher which may cause further flow losses. The results predicted by numerical simulation are in coincident with the experimental ones. It shows that the turbulence model for simulating the flow field in centrifugal pumps is feasible.

High-Temperature Cavity Receiver Integrated with a Short-Term Storage System for Solar MGTs: Heat Transfer Enhancement

Dish-Micro Gas Turbines (MGTs) can be promising systems for power production at small-scale by concentrated solar radiation. Several high-temperature solar receivers have been already designed for such plants, however, nowadays, none of them can assure the proper thermal inertia to level the effects of solar radiation fluctuations on engine performance and safety. In this paper, a solar receiver integrated with a short-term storage system based on high-temperature Phase-Change Materials (PCMs), is proposed. On the basis of a previous preliminary component design and analysis, the receiver geometry has been modified to improve storage capability and heat transfer to the working fluid, reducing temperatures on the irradiated surface making them compatible with material properties and reducing also temperature gradients inside the PCM.Six different geometries, varying length, opening and shape of a front cavity have been analyzed by means of CFD methods. All the configurations have shown a satisfactory behavior in terms of working fluid outlet temperature, storage capabilities and maximum temperatures reached on the surface and inside the receiver. In particular, among them, three geometries can be considered the most promising ones.

Investigation of Combined Transpiration and Opposing Jet Cooling of Sintered Metal Porous Struts

ABSTRACTStruts are used to inject fuel into the supersonic mainstream of scramjet combustion chambers. The leading edge of the strut experiences the maximum temperature due to tremendous aerodynamic heating. This study describes a combined transpiration and opposing jet cooling system for sintered metal porous struts with a jet flowing out of a micro-slit along the stagnation point line against the incoming flow with methane as the coolant. The combined cooling method for the struts is then compared to cooling by the standard transpiration method. The influences of different slit widths and coolant injection conditions on the strut cooling are numerically investigated. The results show that the combined cooling method significantly reduces the maximum strut temperature. The maximum strut temperature decreases but the coolant consumption increases with increasing micro-slit width. Increasing the micro-slit width more effectively balances the increased cooling effectiveness with the increased coolant flow than just increasing the coolant injection pressure. Coolant injection with non-uniform pressures with higher pressure in the front cavity and lower pressure in the back cavity more effectively enhances the cooling effectiveness and reduces the thermal gradient.

Experimental investigation of combined transpiration and film cooling for sintered metal porous struts

A combined transpiration and film cooling method was evaluated experimentally for protecting struts made of sintered stainless steel porous media with film holes on the leading edge in a supersonic wind tunnel. The combined cooling results were compared to standard transpiration cooling of the strut. Schlieren figures show that the film cooling and transpiration cooling had little effect on the flow field stability and the shock wave profiles around the struts for the present conditions. Standard transpiration cooling can protect most of the strut but cannot effectively cool the leading edge even with increased coolant injection pressures. The combined film and transpiration cooling effectively cools both the leading edge and other parts of the strut. Non-uniform coolant injection with higher injection pressures in the front cavity and lower injection pressures in the back cavity more effectively utilized the limited coolant flow. The average cooling efficiency of the front part of the strut increased from 25.7% for standard transpiration cooling to 37.9% for combined transpiration and film cooling with the same coolant consumption using the optimal non-uniform coolant flow distribution.

F3 variability in allophones of /l/: Acoustic-articulatory relations

F3 is know to exhibit higher values in darker varieties of /l/. This contrast has been attributed to differences in closure fronting and front cavity configuration. In this paper we propose a possible alternative explanation for higher F3 in dark /l/, based on sensitivity functions. Both allophones have an apical gesture, but differ in their tongue dorsum gestures: clear /l/ has a raising and fronting gesture, while dark /l/ has postdorsum retraction towards the uvular region. We propose that the gestural composition of dark /l/ creates two constriction sites in the vocal tract that correspond to the two maxima of the F3 sensitivity function, thus resulting in higher values for dark /l/. To address these predictions we analyzed both acoustic and articulatory data from 6 speakers of the Wisconsin XRMB database. Articulatory strategies vary both inter and intra-speakers. High F3 values are obtained with both elevated tongue tip and retracted postdorsum, while low F3 values, have small values of postdorsum retraction. Overall results show that, despite inter-speaker variability in vocal tract shape and articulatory strategies, F3 is positively correlated with tongue dorsum retraction.

Study on the influence of back blade shape on the wear characteristics of centrifugal slurry pump

CFX particle inhomogeneous model was introduced for the mechanism analysis of a centrifugal slurry pump which is equipped with back blades on impeller shrouds. Combining with the total efficiency correction, the simulation showed good prediction accuracy of external characteristics results compared with the experimental values. Vorticity and Q-Criterion were chosen as the variables to illustrate the abrasion morphology and wear mechanism by contrasting simulation result with worn impeller in engineering. The analysis showed that the large vorticity intensity areas are distributed at the edge of impeller shroud and intensively behind the back blades. Moreover, the vorticity scattered on suction surface of back blade shows the largest intensity. The contour of Q-Criterion demonstrated that the swirl scale in front cavity is obviously larger than that in back cavity. The distribution of vorticity on both front and back shrouds can reasonably explain the impeller wear characteristics. Finally, the forward curved back blade proved to be excellence performance in vorticity distribution.

Influence of clearance model on numerical simulation of centrifugal pump

Computing models are always simplified to save the computing resources and time. Particularly, the clearance that between impeller and pump casing is always ignored. But the completer model is, the more precise result of numerical simulation is in theory. This paper study the influence of clearance model on numerical simulation of centrifugal pump. We present such influence via comparing performance, flow characteristic and pressure pulsation of two cases that the one of two cases is the model pump with clearance and the other is not. And the results show that the head decreases and power increases so that efficiency decreases after computing with front and back cavities. Then no-leakage model would improve absolute velocity magnitude in order to reach the rated flow rate. Finally, more disturbance induced by front cavity flow and wear-ring flow would change the pressure pulsation of impeller and volute. The performance of clearance flow is important for the whole pump in performance, flow characteristic, pressure pulsation and other respects.

Prediction of the niche effect for single flat panels with or without attached sound absorbing materials.

The sound transmission loss (STL) of a test sample measured in sound transmission facilities is affected by the opening in which it is located. This is called the niche effect. This paper uses a modal approach to study the STL of a rectangular plate with or without an attached porous material located inside a box-shaped niche. The porous material is modeled as a limp equivalent fluid. The proposed model is validated by comparison with finite element/boundary element computations. Using a condensation of the pressure fields in the niche, the niche effect is interpreted in terms of a modification of the modal blocked pressure fields acting on the panel induced by the front cavity and by a modification of the radiation efficiency of the panel modes due to the presence of the back cavity. The modal approach is then used to investigate the impact of (1) the presence of a porous material attached to the panel on the niche effect and (2) the niche effect on the assessment of the porous material insertion loss. A simplified model for the porous material based on a transfer matrix approach is also proposed to predict the STL of the system and its validity is discussed.