Time-averaged Pressure Research Articles

Transient Simulation for a Pumped Storage Power Plant Considering Pressure Pulsation Based on Field Test

In this study, fast Fourier transform and inverse transform are adopted for noise reduction filtering the data of load rejection pressure of a single unit in a one-tube, four-unit pumped storage power station. Five-spot triple smoothing method is used to extract the time-average and pulsation value of the water hammer pressure of the spiral case and draft tube inlet. The reasonable correction formula is put forward, and the pulsating pressure rise rate of the spiral case (4.44%) and the draft tube inlet (−1.22%) are obtained. A mathematical model is also established for the transition process of the water conveyance and power generation system of the pumped storage power station, and the field single-unit load rejection condition is simulated. The simulation results are consistent with the measurements, and the accuracy of the calculation model in predicting the time-average pressure of water hammer is verified. Thus, the extreme successive load rejection conditions can be simulated based on the proposed model. Combining with the pulsating pressure rise rate of unit, the actual extreme value of extreme working condition is reasonably calculated. The conclusion shows that the pressure of spiral case and draft tube inlet after considering pressure pulsation can meet the control requirements, avoid the damage caused by extreme working condition test to unit, and ensure the operation safety of unit.

High-order accurate simulation of incompressible turbulent flows on many parallel GPUs of a hybrid-node supercomputer

Turbulent incompressible flows play an important role in a broad range of natural and industrial processes. High-order direct numerical simulations are often used for resolving the spatio-temporal scales of such flows. Such high-fidelity simulations require an extensive computational layout which often results in prohibitive computational costs. Recent advances in modern computing platforms, such as GPU-powered hybrid-node supercomputers, appear to become an enabler for high-fidelity CFD at large scales. In this work, we propose methods for accelerating a distributed-memory high-order incompressible Navier–Stokes solver by using NVIDIA Pascal GPUs of a Cray XC40/50 supercomputer. Arithmetically intensive or chronically invoked routines were ported to the GPUs using CUDA C. Host-side driver routines were developed to invoke CUDA C “external” kernels from the FORTRAN legacy code. Numerical methods, for some of the most intensive operations, namely multigrid preconditioners, were modified to be suited to the SIMD standard for graphics processors. Customized unit testing was performed to ensure double-precision accuracy of GPU computations. The optimization layer maintained the memory structure of the legacy code. Post-profiling confirms that backbone distributed memory communications increase the number of dynamic CPU–GPU memory copies, which offsets a part of the computational performance. Strong scalability of the entire flow solver and of the stand-alone pressure solver has been examined on up to 512 P100 GPUs. Strong scaling efficiency decreased for higher numbers of GPUs, probably due to a less favorable communication-to-computation ratio. Weak scalability of the entire solver was tested on up to 4096 P100 GPUs for two problems of different sizes. The solver maintained nearly ideal weak scalability for the larger problem, illustrating the potential of GPUs in dealing with highly resolved flows. The GPU-enabled solver is finally deployed for the scale-resolving simulation of flow transition in the wake of a solid sphere at Re=3700, by utilizing 192 GPUs. The time-averaged pressure coefficient along the sphere surface was in good agreement with previously reported data acquired from CPU-based direct numerical simulations and experiments.

Excessive sound noise risk assessment in textile mills of an Ethiopian-Kombolcha textile industry share company

In countries like Ethiopia, the textile industries are facing a big problem of sound noise pollution. In these countries, the industrial hearing conservation program is not yet clearly developed. Thus, characterizing excessive noise pollutions in textile industries have been the aim of this research project and Kombolcha Textile Mill (KTM) is chosen as the case study. The study is concerned with the noise exposure and its characteristics at the different section of the Textile Mill. Before the actual excessive noise level measurements were collected in the Textile Mill, main areas where measurements were done had to be identified. This was done by prior physical observation and A-Weighted time-averaged sound pressure levels (L_Aeq) survey. More than one hundred walkthrough measurement points were done inside the textile mill. These data were analyzed using MATLAB software packages. Based on our analysis, the spinning and the weaving sections of the mills with its unit processes were identified as potential noise pollution in the factory. On these sections, the measurements were done for 4 – 5 h/d. The instrument used for measurements was a precision integrated portable professional sound level meter. The findings revealed that the KTM employees are working in hazardous environments of above 90 dB, which is the recommended safe limit of noise in the working environment for 8 h used in international standard. As a result an engineering and administration programs which includes different methods of how to control the problem has been recommended for conserving hearing at the KTM.

RANS and hybrid LES/RANS simulations of flow over a square cylinder

Unsteady RANS (URANS), hybrid LES/RANS and IDDES simulations were conducted to numerically investigate the velocity field around, and pressures distribution and forces over a square cylinder immersed in a uniform, steady oncoming flow with Reynolds number Re = 21,400. The vortex shedding responses in terms of Strouhal number, the pressure distribution, the velocity profile and the velocity fluctuations obtained by numerical simulations are compared with experimental data. Compared with 2D URANS simulation, 3D simulations using hybrid LES/RANS and IDDES models provide more accurate prediction on the responses in the wake, including mean streamwise velocity profile and rms velocity fluctuations. This also results in more accurate prediction of time-averaged surface pressure coefficient on the rear surface obtained by 3D hybrid LES/RANS and IDDES simulations than by URANS simulation. When a hybrid LES/RANS model or IDDES model is used, a more accurate prediction for either pressure coefficient or velocity profile (especially in the far wake region) is not guaranteed by increasing the mesh resolution along the spanwise direction of the square cylinder.

Numerical simulation and experiments on turbulent air flow around the semi-circular profile at zero angle of attack and moderate Reynolds number

Two-dimensional flow around a semi-circular profile at the zero angle of attack and at Re = 50000 on the self-oscillatory period is extensively studied by the URANS method involving the standard semi-empirical SST turbulence models, the SST turbulence model with the correction for streamline curvature modified within the Rodi-Leschziner-Isaev and Smirnov-Menter approaches, as well as involving Hanjalic's four-parameter eddy viscosity elliptic relaxation model and its analog - eddy viscosity elliptic blending model proposed in the present work. This has been done with the use of different-structure grids (multiblock with structured overlapping and unstructured composite). Different numerical approximation methods realized in six codes (VP2/3, SigmaFlow, Fluent, CFX, OpenFOAM, and StarCCM+) are used. An underestimation (up to 30%) of time-averaged integral aerodynamic loads is revealed by means of the standard near-wall SST model. This is explained by the high vortex viscosity production in the profile wake. Wind tunnel tests show that the location of cutoff washers on the semi-circular profile provides a quasi-two-dimensional flow around it and allows applying measurement data to verify two-dimensional turbulent flow. The best agreement of experimental results and numerical predictions when comparing the Strouhal number and time-averaged surface pressure coefficient distributions is achieved using both the modified SST model with the correction for streamline curvature and the modified eddy viscosity elliptic blending model. When the SST model with the correction for streamline curvature, modified within the Rodi-Leschziner-Isaev, Smirnov-Menter and Durbin approaches, is used, all the above codes yield close predictions of a vertical aerodynamic load on the oscillation period.

Investigation of velocity and temperature measurement sensitivities in cross-correlation filtered Rayleigh scattering (CCFRS)

The cross-correlation filtered Rayleigh scattering method is presented for planar measurements of time-averaged velocity, temperature, density, and pressure using laser scanning, Rayleigh scattering, and cross-correlation-based signal processing. Of particular note, the methods and analyses presented show that velocity and temperature measurements are obtainable at acceptable uncertainties for many aerodynamic applications with or without particles present. In the current work, velocity and temperature measurement uncertainties for this method are analysed by Monte Carlo simulations and evaluation of the Cramér–Rao lower bounds for the signals generated in this approach with aerodynamic applications in mind. A key aspect considered is the relative strength of Rayleigh (molecular) scattering and Mie (particle) scattering contributions to the simulated flow signal. Compared to particle-based velocity estimation, the effects due to convolution between the molecular filter and the broadband Rayleigh scattering spectrum are found to increase the estimator variance of the velocity. For given flow conditions, the velocity error associated with the signal processing routine with noise-free signals is found to be less than , and bias error associated with discrete sampling in the laser frequency domain is within . For these same conditions, temperature measurement simulations indicate bias error bounds of 0. 014% with random uncertainty bounds of less than ±1.4% for a signal with no Mie scattering contribution, and bias error bounds of less than ±0.14% with random uncertainty bounds of less than 3.2% for flows contaminated with Mie scattering sources at a signal-to-noise ratio of 25 dB or greater. This technique is also being further developed to measure density and pressure using the principles of laser Rayleigh scattering in flows containing particles of unknown sizes and concentrations.

Numerical study on the flow characteristics in swirl meter

The swirl meter (vortex precession flow meter) popularly used in natural gas industry is a kind of velocity flow meter with high turndown ratio and well performance in low flow measurement and other known advantages. In order to further understand the flow pattern of swirl meter to further improve its performance, computational fluid dynamics simulations are used to simulate the flow and predict the coefficient for swirl meter at different flow rates. Using renormalization group k–ε turbulent model and SIMPLEC algorithm, numerical simulations have been performed through commercial codes Fluent, and meter coefficients are also obtained experimentally to validate the numerical results. The simulated velocity and pressure in swirl meter are analyzed in detail, which are time-averaged distributions during a time period based on the transient numerical simulation. It is found that centerline pressure is lowest at the outlet of the swirler and rises gradually along the axial direction. While near-wall pressure presents an opposite variation tendency, it is significantly low at the end of throat due to strong influence of vortex precession. Centerline velocity increases as the flow approaches throat and reaches its maximum at center region of throat, and then it decreases and keeps relatively stable at downstream of divergent section. Both time-averaged pressure and axial velocity distributions are axisymmetric, and pressure variation is small on the cross section at the end of throat, although vortex precession is strong.

Numerical investigation on turbulent oscillatory flow through a jet pump.

A jet pump with an asymmetrical channel can induce a time-averaged pressure drop in oscillatory flow, which can effectively suppress Gedeon streaming in looped thermoacoustic engines. In this work, the flow characteristics and time-averaged pressure drop caused by a jet pump in turbulent oscillatory flow are investigated through numerical simulation. Through the analysis of the dimensionless governing equations, the emphasis is put on the effects of Womersley number and maximum acoustic Reynolds number on the performance of the jet pump. Meanwhile, the steady flow resistance coefficients are also measured numerically. The results indicate that the oscillatory flow resistance coefficients are relatively insensitive to Womersley number when it is less than 46. Moreover, the oscillatory flow resistance coefficients agree well with the steady state flow results, which validate the quasi-static assumption in turbulent oscillatory flow. However, further increasing Womersley number will lead to a reduction in the time-averaged pressure drop. The simulation method and results, as well as the hydrodynamic mechanism beneath the results, are presented and discussed in detail.

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.

Flat vs. curved rigid-lid LES computations of an open-channel confluence

Abstract This paper describes the application of four Large Eddy Simulations (LES) to an open-channel confluence flow, making use of a frictionless rigid-lid to treat the free-surface. Three simulations are conducted with a flat rigid-lid, at different elevations. A fourth simulation is carried out with a curved rigid-lid which is a closer approximation to the real free-surface of the flow. The curved rigid-lid is obtained from the time-averaged pressure field on the flat rigid-lid from one of the initial three simulations. The aim is to investigate the limitations of the free-surface treatment by means of a rigid-lid in the simulation of an asymmetric confluence, showing the differences that both approaches produce in terms of mean flow, secondary flow and turbulence. After validation with experimental data, the predictions are used to understand the differences between adopting a flat and a curved rigid-lid onto the confluence hydrodynamics. For the present flow case, although it was characterized by a moderately low downstream Froude number (Fr ≈ 0.37), it was found that an oversimplification of the numerical treatment of the free-surface leads to a decreased accuracy of the predictions of the secondary flow and turbulent kinetic energy.

Aerodynamic drag determination of a full-scale cyclist mannequin from large-scale PTV measurements

The aerodynamic drag of a human-scale wind tunnel model is obtained from large-scale particle tracking velocimetry measurements invoking the conservation of momentum in a control volume surrounding the model. Lagrangian particle tracking is employed to obtain the velocity and static pressure statistics in a thin volume in the wake of a cyclist mannequin at freestream velocities between 12.5 and 15 m/s, corresponding to Reynolds numbers from 5 times 105 to 6 times 105 based on the torso length. The spatial distributions of the time-average streamwise velocity and pressure coefficient match well with previous works reported in literature. The streamwise velocity fluctuations in the wake of the cyclist’s model are presented, clearly demonstrating the unsteady nature of the main wake flow structures. Furthermore, the obtained aerodynamic drag follows the expected quadratic increase with increasing freestream velocity. The accuracy of this drag estimation is evaluated by comparison to force balance data and corresponds to 30 drag counts. The three terms composing the overall drag force, ascribed to the mean and fluctuating streamwise velocity and the mean pressure, are also evaluated separately, demonstrating that the resistive force is dominated by the contribution of the mean streamwise momentum deficit, whereas the contribution of the pressure term is negligible.Graphical abstract

Effects of a sweeping jet actuator on aerodynamic performance in a linear turbine cascade with tip clearance

Sweeping jet actuator as a fresh attempt has been applied in controlling flow separations and improving aerodynamic performances in a linear turbine cascade with tip clearance. In the present study, the oscillating jet process of sweeping jet actuator in the tip clearance was illustrated and a potential advantage from a system integration perspective was validated by an unsteady numerical study. The excitation frequencies and excitation modes were also investigated for achieving the further understanding of the mechanism of sweeping jet actuator for controlling flow separations. By using sweeping jet actuator, the flow separation near the upper endwall was delayed and the flow loss at the outlet of the cascade was reduced. For the optimal case, the time-averaged total pressure loss decreased by about 11.7% with the jet flow rate of only 0.35% of the inlet flow rate. In addition, it was found that there exists an optimum frequency to achieve the optimum controlling effects on the flow separations. Because of the blockage of tip leakage flow at the local gap by the high-momentum fluid from sweeping jet actuator, the controlling effects on the tip leakage vortex loss were better than that on the passage vortex loss. Through the use of four excitation modes in this study, the total pressure losses at the outlet were all reduced in different degrees. Under the present boundary conditions and working parameters, the unsteady controlling mode of sweeping jet actuator was found to perform much better than the other steady modes.

Computational study on the effect of orifice-edge-chamfered angle on the synthetic jet characteristics

The effect of chamfered orifice edges on the time-averaged pressure difference and jet velocity of synthetic jet have been numerically investigated. Chamfered orifice edges with exit angle of 15° and 30° are analysed. Moving grid is utilised to define the moving diaphragm of the actuator. The results are validated against experimental data. The time-averaged pressure difference between the location inside the orifice duct and downstream region where the velocity becomes negligible have been numerically predicted for all the cases. The jet velocity is predicted numerically at the downstream location of 1 mm from the orifice exit. The overall results indicated that the changes of chamfered orifice edges give significant impact on the time-averaged pressure difference. The jet velocity is also affected by the variation of the chamfer orifice edges during the expulsion stage. The findings from this study provides a basic design guideline for designing a synthetic jet actuator with lower minor loss and power dissipation.

Influences of Domain Symmetry on Supersonic Combustion Modeling

High-fidelity Improved Delayed Detached Eddy Simulation modeling is applied to examine the influence of the symmetry plane on the supersonic flow and combustion characteristics in a round-to-elliptic–transition scramjet combustor. A quarterly split domain and the full domain are modeled by using up to 0.14 billion cells and a third-order scale-selective discretization scheme. The combustion chemistry is described by the finite-rate partially stirred reactor model based on multicomponent diffusion and a skeletal kerosene mechanism with 19 species/53 reactions. Time-averaged pressure, temperature, Mach number, and heat release rate are compared to examine the influence of the symmetry assumption on the mean flow fields. The exchanges of mass, momentum, and energy across the symmetry planes are analyzed. Considerable increases in the combustion efficiency and total pressure loss occur when applying the full domain, although with the similar mixing efficiency. Turbulence spectrum analysis confirms the power-law for supersonic flows, and the inertial subrange is found to be shorter in the quarter-domain modeling. A comparison of the Borghi’s diagrams shows that the data points shift from the flamelet mode to the thin reaction zone mode when using the full domain, and at least of them cannot be described by fast-chemistry combustion models.

Experimental and Numerical Investigation of Optimized Blade Tip Shapes—Part I: Turbine Rainbow Rotor Testing and Numerical Methods

Blade tip design and tip leakage flows are crucial aspects for the development of modern aero-engines. The inevitable clearance between stationary and rotating parts in turbine stages generates high-enthalpy unsteady leakage flows that strongly reduce the engine efficiency and can cause thermally induced blade failures. An improved understanding of the tip flow physics is essential to refine the current design strategies and achieve increased turbine aerothermal performance. However, while past studies have mainly focused on conventional tip shapes (flat tip or squealer geometries), the open literature suffers from a shortage of experimental and numerical data on advanced blade tip configurations of unshrouded rotors. This work presents a complete numerical and experimental investigation on the unsteady flow field of a high-pressure turbine, adopting three different blade tip profiles. The aerothermal characteristics of two novel high-performance tip geometries, one with a fully contoured shape and the other presenting a multicavity squealer-like tip with partially open external rims, are compared against the baseline performance of a regular squealer geometry. The turbine stage is tested at engine-representative conditions in the high-speed turbine facility of the von Karman Institute. A rainbow rotor is mounted for simultaneous aerothermal testing of multiple blade tip geometries. On the rotor disk, the blades are arranged in sectors operating at two different clearance levels. A numerical campaign of full-stage simulations was also conducted on all the investigated tip designs to model the secondary flows development and identify the tip loss and heat transfer mechanisms. In the first part of this work, we describe the experimental setup, instrumentation, and data processing techniques used to measure the unsteady aerothermal field of multiple blade tip geometries using the rainbow rotor approach. We report the time-average and time-resolved static pressure and heat transfer measured on the shroud of the turbine rotor. The experimental data are compared against numerical predictions. These numerical results are then used in the second part of the paper to analyze the tip flow physics, model the tip loss mechanisms, and quantify the aero-thermal performance of each tip geometry.

Investigation on the Stall Inception Circumferential Position and Stall Process Behavior in a Centrifugal Compressor With Volute

The present paper numerically and experimentally investigates the stall inception mechanisms in a centrifugal compressor with volute. Current studies about stall inception pay more attention on the axial compressors than the centrifugal compressors; especially, the circumferential position of stall inception onset and the stall process in the centrifugal compressor with asymmetric volute structure have not been studied sufficiently yet. In this work, the compressor performance experiment was conducted and the casing wall static pressure distributions were obtained by 72 static pressure sensors first. Then, the full annular unsteady simulations were carried out at different stable operating points, and the time-averaged static pressure distributions were compared with the experimental results. Finally, the stall process of the compressor was investigated by unsteady simulations in detail. Results show that the stall inception onset is determined by the impeller leading edge (LE) spillage flow, and the occurrence time of trailing edge (TE) backflow is prior to the LE spillage. The nonuniform static pressure circumferential distribution at impeller outlet induced by volute tongue causes the two stall inception regions locating at certain circumferential positions, which are 120 deg and 300 deg circumferential positions at impeller LE, corresponding to the circumferential static pressure peak (PP) and bulge regions at impeller outlet, respectively. In detail, at rotor revolution 2.86, a small disturbance that the incoming/tip clearance flow interface is perpendicular to axial direction occurs at 120 deg position, but this disturbance did not cause the compressor stall. Then at revolution 7, the first stall inception zone (spillage region) occurs at 120 deg position, causing the compressor stall with positive pressure ratio performance. At approximately revolution 23, the second stall inception zone occurs at about 300 deg position; however, both the intensity and size of this stall inception zone are smaller than those of the first stall inception zone. These two stall inception zones are not moving along circumferential direction because the stall inception circumferential position is dominated by the impeller outlet static pressure distribution. Even then, the obvious low frequency signals appear after the spillage crossing two blade LEs, because at this moment, the spillage vortex caused by the tip leakage flow begins to shed. However, due to the asymmetric structure limitation, this vortex cannot move across full annular. Furthermore, the spillage vortexes cause the local low static pressure zone ahead of blade LE in the centrifugal compressor with volute, suggesting that the spillage can be predicted by the steady casing wall static pressure measuring. The development of blockage zones at impeller LE is also investigated quantitatively by analyzing the stall blockage effect.

Numerical Simulation of Hydraulic Characteristics in A Vortex Drop Shaft

A new type of vortex drop shaft without ventilation holes is proposed to resolve the problems associated with insufficient aeration, negative pressure (Unless otherwise specified, the pressure in this text is gauge pressure and time-averaged pressure) on the shaft wall and cavitation erosion. The height of the intake tunnel is adjusted to facilitate aeration and convert the water in the intake tunnel to a non-pressurized flow. The hydraulic characteristics, including the velocity (Unless otherwise specified, the velocity in this text is time-averaged velocity), pressure and aeration concentration, are investigated through model experiment and numerical simulation. The results revealed that the RNG k-ε turbulence model can effectively simulate the flow characteristics of the vortex drop shaft. By changing the inflow conditions, water flowed into the vertical shaft through the intake tunnel with a large amount of air to form a stable mixing cavity. Frictional shearing along the vertical shaft wall and the collisions of rotating water molecules caused the turbulence of the flow to increase; the aeration concentration was sufficient, and the energy dissipation effect was excellent. The cavitation number indicated that the possibility of cavitation erosion was small. The results of this study provide a reference for the analysis of similar spillways.

A New Index to Evaluate the Potential Damage of a Surge Event: The Surge Severity Coefficient

Industrial compressors suffer from strong aerodynamic instability that arises when low ranges of flow rate are achieved; this instability is called surge. This phenomenon creates strong vibrations and forces acting on the compressor and system components due to the fact that it produces variable time-averaged mass flow and pressure. Therefore, surge is dangerous not only for aerodynamic structures but also for mechanical parts. Surge is usually prevented in industrial plants by means of anti-surge systems, which act as soon as surge occurs; however, some rapid transients or system upsets can lead the compressor to surge anyway. Despite the fact that surge can be classified as mild, classic, or deep, depending on the amplitudes and frequency of the fluctuations, operators are used to simply referring to surge, without making a distinction between the three main classes. This is one of the reasons why, when surge occurs in industrial plants, it is a common practice to stop the machine to perform inspections and check if any damage occurred. Obviously, this implies maintenance costs and time, during which the machine does not operate. On the other hand, not all surge events are dangerous in terms of damage, and they can be tolerated by the mechanical structures of the compressor; thus, in these cases, inspections would not be required. Unfortunately, a method for establishing the potential damage of a surge event is not available in literature. In order to fill this gap, this paper proposes a final formulation of a surge severity index, which was only preliminarily formulated by the authors in a previous work. The preliminary form of this coefficient demonstrated some limitations, which are overcome in this paper. The surge severity index derives from an energy-force based analysis. The coefficient demonstration is carried out in this paper by means of (i) the application of the Buckingham's Pi-theorem, and (ii) a careful analysis of the causative and restorative factors of surge. Finally, some simple practical evaluations are shown by means of a sensitivity analysis, using simulation results of an existing model, to effectively further highlight the consistency of this coefficient for industry.

Numerical Study of the Axial Gap and Hot Streak Effects on Thermal and Flow Characteristics in Two-Stage High Pressure Gas Turbine

Combined cycle power plants (CCPPs) are becoming more important as the global demand for electrical power increases. The power and efficiency of CCPPs are directly affected by the performance and thermal efficiency of the gas turbines. This study is the first unsteady numerical study that comprehensively considers axial gap (AG) in the first-stage stator and first-stage rotor (R1) and hot streaks in the combustor outlet throughout an entire two-stage turbine, as these factors affect the aerodynamic performance of the turbine. To resolve the three-dimensional unsteady-state compressible flow, an unsteady Reynolds-averaged Navier–Stokes (RANS) equation was used to calculate a k − ω SST γ turbulence model. The AG distance d was set as 80% (case 1) and 120% (case 3) for the design value case 2 (13 mm or d/Cs1 = 0.307) in a GE-E3 gas turbine model. Changes in the AG affect the overall flow field characteristics and efficiency. If AG decreases, the time-averaged maximum temperature and pressure of R1 exhibit differences of approximately 3 K and 400 Pa, respectively. In addition, the low-temperature zone around the hub and tip regions of R1 and second-stage rotor (R2) on the suction side becomes smaller owing to a secondary flow and the area-averaged surface temperature increases. The area-averaged heat flux of the blade surface increases by a maximum of 10.6% at the second-stage stator and 2.8% at R2 as the AG decreases. The total-to-total efficiencies of the overall turbine increase by 0.306% and 0.295% when the AG decreases.

Three-dimensional numerical thrust performance analysis of hydrogen fuel mixture rotating detonation engine with aerospike nozzle

The propulsive performance for an H2/O2 and H2/Air rotating detonation engine (RDE) with conic aerospike nozzle has been estimated using three-dimensional numerical simulation with detailed chemical reaction model. The present paper provides the evaluation of the specific impulse (Isp), pressure gain and the thrust coefficient for different micro-nozzle stagnation pressures and for two configurations of conic aerospike nozzle, open and choked aerospike. The simulations show that regardless of the nozzle, increase the micro-nozzles stagnation pressure increases the mass flow rate, the pre-detonation gases pressure and consequently the post-detonation pressure. This gain of pressure in the combustion chamber leads to a higher pressure thrust through the nozzle, improving the Isp. It was also found that the choked nozzle increases the chamber time-averaged static pressure by 50–60% compared with the open nozzle, inducing higher performance for the same reason explained before.