Average Total Pressure Research Articles

Aerodynamic optimization method of intake grille of active clearance control system for turbines based on modified social spider algorithm (MSSA)

During the operation of an active clearance control (ACC) system of a turbine, the aerodynamic performance of the intake grille indirectly influences its control. To improve the performance, an aerodynamic optimization method is proposed, consisting of parameterization, an optimization algorithm, and a fitness evaluation. During parameterization, its geometry is represented by seven geometric variables. A modified social spider algorithm is used as the optimization algorithm. To evaluate the aerodynamic performance of the grille, a special fitness function is adopted, obtained using an adaptive topological multi-layer feedforward artificial neural network. To verify the feasibility of this method, experiments and numerical calculations are carried out on the original and optimized intake grilles. The results show that the average intake flow rate and average total pressure recovery coefficient of the optimized grille have increased by 17.3% and 4.9%, respectively.

Analysis of Tangential Leakage Flow Characteristics in a Variable Diameter Dual Circular Arc Vortex Compressor

(1) To address issues such as a low compression ratio and severe leakage in uniform wall thickness vortex compressors, this paper adopts a new scroll compressor model with a variable diameter double arc combined profile, which has a larger pressure ratio and smaller leakage than the scroll compressor with equal wall thickness that can bring new ideas and methods to the research in the field of scroll compressors. (2) This paper determines the theoretical equation of the variable diameter dual circular arc vortex profile and the combined profile, and infers mathematical models for the leakage line length, working chamber volume, and gas leakage per unit rotation angle of the vortex compressor, followed by simulation. (3) The results show that compared to the uniform wall thickness involute profile, the variable diameter dual circular arc combined profile model reduces the leakage line length by 25%, increases the average total pressure at the working chamber outlet by 2.38%, and decreases the leakage amount by 3.2%, consistent with theoretical analysis. (4) The tangential leakage caused by the radial gap in the variable diameter dual circular arc combined profile model has a significant impact on the uneven distribution of temperature and velocity fields in the working chamber of the vortex compressor, but a smaller impact on the pressure field.

Numerical Investigation of a Vortex Diverter Designed for Improving the Performance of the Submerged Inlet

The submerged inlet exhibits good stealth characteristics and lower drag, but it has a low total pressure recovery coefficient and high distortion rate, which limits its widespread application. This paper proposes a vortex diverter aimed at enhancing the performance of the submerged inlet and investigates the aerodynamic coupling mechanism between the vortex diverter and the submerged inlet in detail. Firstly, based on the flow field characteristics of the submerged inlet, the design principles of the vortex diverter are proposed. Then, the impact of the vortex diverter on the flow field of the submerged inlet is analyzed using the numerical method. Finally, the matching design between the vortex diverter and the submerged inlet is explored. The results show that the vortex diverter improves the average total pressure of the airflow inside the inlet by exhausting the low-energy flow from the larger radius side of the inlet, thereby suppressing flow separation and enhancing flow field uniformity. The vortex diverter improves the intake performance of the submerged inlet under different incoming flow Mach numbers, inlet exit Mach numbers, angles of attack, and small sideslip angles. The maximum increase in the total pressure recovery coefficient is 3.1099%, and the maximum reduction in the circumferential total pressure distortion is 49.5207%. Among the design parameters, the horizontal distance between the leading edge of the vortex diverter and the inlet lip has the greatest influence on the intake performance, and the best control effect is achieved when the vortex diverter is installed at the throat position. Furthermore, after installing the vortex diverter, reducing the side-edge angle of the entrance appropriately can effectively reduce the intensity of the secondary flow, thereby improving the total pressure recovery at the exit and reducing the distortion rate.

Optimization of a centrifugal pump with high efficiency and low noise based on fast prediction method and vortex control

This study aims to develop a rapid optimization design method for the centrifugal pump with high efficiency and low noise. The improved delayed detached eddy simulation and Powell's vortex sound method were employed to calculate the flow and sound field. The prediction models of hydraulic loss and noise based on vortex characteristic quantities were built using linear regression (LR) and artificial neural network (ANN) methods respectively. The Kriging surrogate model and the NSGA-II genetic algorithm were utilized for minimizing the entropy production rate and average total sound pressure in the pump, where the objectives of the training dataset for Kriging model were calculated by prediction model (scheme I) and conventional unsteady numerical simulation (scheme II). Results show that the structure and performance of optimized pumps under both schemes are nearly identical, but the computational cost of scheme Iis much lower than that of scheme II. The shear of the optimized pump is significantly reduced and the rigid rotational strength is enhanced, leading to head and efficiency improved by 3.2 % and 3.7 % respectively, under the design flow condition. The average total sound pressure level is reduced by 1.07 % due to the fluctuation suppression of shear and rigid vorticity.

Simple pseudo-steady state productivity index correlations for infinite-conductivity horizontal wells based on a rigorous, semi-analytical model

Simple pseudo-steady state (PSS) productivity index (PI) correlations are developed for horizontal wells producing at a constant rate from a closed, rectangular reservoir based on a rigorous infinite-conductivity model (ICM). The main three correlations are functions of the half-length wellbore segments number (mt) only and mt can be determined by the general correlation, which is a function of dimensionless well length (LD). The correlations are developed by using a nonlinear regression technique (with zero error) based on over thousand semi-analytical runs for a rigorous ICM covering 90 cases of different well and reservoir configurations. The 90 cases are averaged with less than 5% error in the total pressure drop calculation for the most of them to reduce the number of correlations and to remove the slight effect of well penetration ratio (PR). The PSS PI correlations are simply used to calculate mt, average pressure drop at transient-state, average starting time of PSS, and average total pressure drop at the beginning of PSS. At PSS, the reservoir outer boundaries are dominant, and the pressure drop will depend on the temporal and the spatial time-independent functions. The simple PSS PI correlations have been verified, and can be easily implemented in a standard spreadsheet code.The results show that LD is directly proportional to PSS PI and more significant than reservoir thickness (h) on horizontal-well productivity evaluation, which confirms the principle of the economic feasibility for drilling horizontal well in the oil industry. The results also show that the horizontal-well productivity by this study is several times higher than its counterparts by the methods reported in the literature because the method used by this study is based on a rigorous infinite-conductivity solution where no significant pressure drop occurs, while the previous methods are based on approximate infinite-conductivity solutions (AICSs). Therefore, there is a big underestimation in productivity calculation by using the previous methods which crucially reflect on reservoir evaluation. The new correlations give accurate PSS PI for over 3000 cases of diverse well and reservoir configurations, besides giving a rough PSS PI for the other cases.

Design of sinusoidal-shaped inlet duct for acoustic mode modulation noise reduction of cooling fan

The noise reduction method of installing a sinusoidal-shaped inlet duct on a cooling fan is analyzed theoretically and experimentally in terms of the acoustic mode modulation. Based on Lowson's point force model, the correlation between the free field noise and acoustic mode of the fan rotor and the unsteady forces on the rotor blade surface is established. The azimuthal acoustic mode is demonstrated to partially reflect the composition and intensity of the acoustic source. The theoretical variation in azimuthal acoustic mode indicates that it is possible to completely cancel each mode simultaneously when the phase differences of forces of each order in the secondary source are controlled. A sinusoidal-shaped inlet duct noise reduction structure controlled by a parameter equation is proposed, and the preferred parameter selection is given by the far-field noise measurements. The results of azimuthal mode decomposition exhibit a similar trend to the theoretical analysis. Compared with the straight duct, the chosen sinusoidal-shaped inlet duct achieved greater noise reduction at the blade passing frequency and its first harmonic. The average total sound pressure level in the far field was 6.0 dBA lower than that of the prototype fan, and 1.4 dBA lower than that of the straight duct model.

CFD based modeling of OWC device positioned over stepped bottom

This research deals with various parameters associated with the hydrodynamics of an OWC device positioned over the stepped bottom. The problem is solved using the multiphase based CFD technique in “ANSYS Fluent software”. A “piston type wavemaker” and dynamic meshing technique are employed to produce the incident wave inside the numerical wave tank (NWT). Further, “volume of fluid” procedure is implemented to produce the free surface in the NWT. The “free surface elevation” is analyzed in various instant of time. Contour plots of the dynamic pressure, turbulent kinetic energy and turbulent intensity associated with the fluid motion are provided. Further, the variation of the vertex average total pressure and vertex average y− velocity at the orifice on the OWC device’s top wall are analyzed with respect to flowtime.

A characterization of unsteady effects for transonic turbine airfoil limit loading

To better understand the effect of vortex shedding on the nature of the trailing edge shock system during airfoil limit loading a computational fluid dynamic investigation was performed for a transonic turbine airfoil at sublimit, limit and supercritical conditions. Four modeling strategies were employed: steady state RANS, unsteady RANS, DDES, and turbulence model free. The influence of transient modeling approaches on the predicted mass-flow averaged total pressure loss coefficient, mass-flow averaged flow angles, and on the limit loading pressure ratio were found to be insignificant with the exception of the URANS model during critical loading. It was found that the URANS modeling approach failed to predict the transition from near trailing edge dominated vortex formation to base pressure vortex formation resulting in a drastic rise in predicted total pressure loss. Surface isentropic Mach distributions were predicted similarly for all modeling strategies, with the exception of the trailing edge base pressure region and points of shock impingement along the suction surface. A detailed review of the boundary layer states at the trailing edge was performed. It was found that all of the modeling approaches predicted laminar boundary layer profiles along the pressure surface trailing edge and turbulent profiles along the suction surface. The predicted base pressure distributions were also reviewed, showing the base pressure to decrease with increasing pressure ratio. The unsteady simulation approaches consistently predicted lower average surface pressures than the steady state RANS simulations. Qualitative images of the numerical Schlieren contours were presented and reviewed showing large differences in the prediction of vortex shape, size, and subsequent shock influence.

Study on the aerodynamic performance of nacelle inlet under crosswind

Flow separation will occur in the nacelle inlet under crosswind operation, which will result in engine intake distortion and even engine surge. To study the reference characteristics of the flow field of the short tank inlet separation under the influence of crosswind, this paper observed the cloud map of the total price loss coefficient by changing the flow deflection Angle and flow velocity, made a qualitative analysis of the total pressure distortion degree, then calculated the average total pressure loss coefficient and distortion index, and conducted a quantitative analysis to explore the improvement of the total pressure distortion under different flow field factors. The results show that the degree of total pressure distortion is improved with the increase of incoming flow velocity at a small inlet deflection Angle, but with the increase of incoming flow deflection Angle, the ability of incoming flow velocity to improve the total pressure distortion gradually weakens until it disappears. The inlet deflection Angle plays a decisive role in the improvement effect of incoming flow velocity on the total pressure distortion.

Numerical study on the integration of supersonic turbine guide vanes and three-dimensional hydrogen/air rotating detonation combustor

Hydrogen/air rotating detonation turbine engine is expected to become a new generation of aerospace power plant because of its compact structure, high cycle thermal efficiency, and superior thrust performance. It can also reduce fuel consumption, save energy, and reduce carbon emissions. However, the highly unsteady oscillation characteristics of the outlet flow of the rotating detonation combustor make it difficult to integrate the supersonic turbine with the rotating detonation combustor. In this paper, the supersonic turbine guide vanes are designed by the method of characteristics and Bessel parameterization and are integrated with three-dimensional hydrogen/air rotating detonation combustors for numerical studies. The effects of aligned mode and misaligned mode on the coupling of supersonic turbine guide vanes and rotating detonation combustor are discussed carefully. The results show that the supersonic turbine guide vanes can make the rotating detonation wave change from a single-wave mode to a double-wave alternating strength and weak propagation mode. It can effectively suppress the oscillation of the combustion chamber outlet airflow. In the aligned mode, the peak pressure at the outlet of the supersonic turbine is about 70% lower than that at the cascade inlet, the pressure oscillation amplitude is reduced by 93.33%, and the temperature amplitude is reduced by 23.81%; the average total pressure loss coefficient of the cascade is 11.63%. In the misaligned mode, compared with the cascade inlet, the peak value of the pressure signal at the cascade outlet decreases by about 50%, while the pressure oscillation amplitude decreases by about 33.33%, and the temperature oscillation amplitude decreases by 11.11%; the average total pressure loss coefficient of the cascade is 4.83%. The supersonic turbine guide vanes have a better suppression effect on the oscillation signal in the aligned mode, but the relative total pressure loss is relatively large. This is because that the oblique shock wave, channel shock wave, and supersonic turbine guide vanes interact to generate more complex wave system and secondary flow in the aligned mode. These features provide important reference information for the coupling of supersonic turbines and rotating detonation combustors.

Flow Separation Control of Nacelle Inlets in Crosswinds by Dielectric Barrier Discharge Plasma Actuation

Crosswinds will lead to large-scale flow separation in the nacelle inlets, which seriously affects the flight safety of the aircraft; there is an urgent need to develop flow control measures. As a plasma flow control method, the application of surface dielectric barrier discharge in the field of nacelle inlet separation control is of great significance for improving the intake quality. Based on the characteristic law of the baseline flow field, the flow control effect of the nacelle inlet separation flow field experiments with NS-DBD, and the influence of the actuation frequency on the flow control is discussed. A comparative experimental study of NS-DBD and AC-DBD is carried out. Finally, the flow control mechanisms for both are discussed. The results show that under the condition that the flow velocity of the wind tunnel is 35 m/s and the crosswind angle is 10°, the average total pressure loss coefficient and distortion index decrease by 29.62% and 44.14% by NS-DBD actuation. At the same time, exists an inherent optimal coupling frequency in NS-DBD, and the control effect of NS-DBD is better than that of AC-DBD. NS-DBD mainly through shock waves and induced vortices, while AC-DBD mainly through the induced generation of near-wall jets to reduce the inverse pressure gradient and improve nacelle flow separation.

Three-dimensional numerical study on the interaction between RDC and NGV

In this paper, the three-dimensional numerical method is used to study the change of the internal flow field distribution characteristics of a RDC with a deflector installed at the outlet, using the premixed gas of kerosene and air as reactants. It is found that the total pressure in the front section of the combustor has been improved. Different configurations of deflectors were designed. It was found that the flow field in the combustion chamber could not be significantly changed by changing the number of blades, but the maximum average total pressure and the total pressure loss in the mixing section could be effectively improved by adjusting the angle of incidence. Because the propagation direction of rotating detonation wave and the deflector blade have directionality, the study found that when the two directions are opposite, the reflected shock wave formed at the inlet of the deflector changes greatly, the working environment of the fixed blade is worse, the uniformity of gas after passing the deflector decreases, the flow field along the axial average total pressure loss increases significantly, and the peak value of the total pressure shifts significantly downstream. The study of the interaction between NGV and RDC provides a basis for the design of the rotaing detonation turbine engine.

Abstract 522: Computational Fluid Dynamics Analyses Of Geometric Incompatibility And Seal Zone Stability In Endovascular Aneurysm Repair

Introduction: Long-term durability of endovascular aneurysm repair (EVAR) is often compromised due to inadequate sealing of the endograft to the aorta. We hypothesize that geometric mismatch between the aorta and endograft can lead to the development of bird-beak regions, type Ia endoleaks, and endograft migration. Our novel computational model shows how geometric incompatibility at the seal zone contributes to endoleak formation and propagation. Methods: Using finite-element modeling, we simulated endograft crimping and deployment in pressurized aortic models with different degrees of curvature (0°, 30°, 60°) and oversizing (0%, 20%, 25%). We then performed computational fluid dynamics (CFD) modeling with a detailed pressure analysis of various regions along the length of each model. Results: Across our models, pressure gradients developed between the bulk flow and endoleak regions. For all degrees of curvature, the average total pressure in the endoleak region was higher than that of the bulk flow in the 20% and 25% oversized models. While oversizing decreased the aorta-endograft geometric mismatch in the 60° model and mitigated the volume of endoleak, too much oversizing in the 0° models worsened endoleak. Conclusions: We present one of the first computational models to study the sensitivity of seal zone mechanics to the degree of aorta-endograft mismatch. Our finding of pressure gradients that exist between the endoleak and bulk flow may represent regions of high mechanical instability that may further propagate the endoleak. Our results highlight the importance of shape and oversizing considerations when selecting the appropriate endovascular therapy for EVAR patients. Figure 1: CFD simulations of aorta-endograft models with different degrees of curvature and oversizing show endoleak formation as a function of geometric incompatibility.

An analytical solution for consolidation of soils with stone columns and vertical drains by considering the deformation of stone columns

The composite foundation reinforced by stone columns and vertical drains is widely used in various projects. However, available calculation methods for such consolidation are rarely reported in the literature. Firstly, a set of basic equations are proposed to describe the seepage relations among stone columns, vertical drains, and soft soils in this study. Then, the governing consolidation equation, in which the average total excess pore water pressure (EPWP) serves as a variable, is derived by considering the deformation of stone columns during consolidation under the assumption of equal strain conditions. Moreover, the analytical solution for the consolidation equation is obtained by the method of separation of variables, and its reliability is verified by degenerating into the solution for the consolidation of composite foundations reinforced by stone columns and comparing it with the field measurements. Finally, a parametric study is performed to investigate the consolidation behavior. The results show that the consolidation rate can be significantly increased by installing vertical drains between the stone columns compared to reducing the column spacing; for some composite foundations reinforced by stone columns with a high ratio of replacement, the deformation of columns during consolidation cannot be ignored; the smear effect caused by vertical drains can be ignored in such composite foundations.

An Experimental Facility with the High-Speed Moving Endwall for Axial Compressor Leakage Flow Research

The moving endwall has a great influence on the development and stability of axial compressor leakage flow. This paper presents a novel experimental facility with a high-speed moving endwall for studying axial compressor leakage flow. The uniqueness of the design concept is that using a large disk simulates the high-speed moving endwall. When R/Cx = 16, theoretical analysis shows that the maximum linear velocity difference is about 2.5% while the maximum axial velocity difference of the mid-three passages is less than 5%. Single-passage simulations show that the disk radius of R/Cx = 16 can achieve an acceptable accuracy in terms of static pressure, total pressure, and density flow. Seven-passage simulations confirm that the mid-three passages have small errors from the axial velocity difference. Subsequently, preliminary experimental results obtained from the experimental facility are presented. The results reveal that the moving endwall significantly changes the distributions of the total pressure loss and static pressure coefficient. The relative difference in the averaged total pressure loss between the experiment and CFD is 11.33% and 7.69% for the static and moving endwall, respectively. It is expected that the experimental facility will make more useful contributions to the understanding of axial compressor leakage flow in the future.

Cooling fan aerodynamic noise reduction with short inlet duct and its applicability

This paper presents experimental and numerical analyses of the noise-reduction method of applying short inlet ducts to axial-flow cooling fans. Far-field noise tests of three different-sized cooling fans with tip Mach numbers of 0.143, 0.156, and 0.174 demonstrated that tonal noise was the primary source of aerodynamic noise. Through the installation of short inlet ducts on these fans, the upstream propagation of tonal noise was reduced. The average total sound pressure levels were decreased by up to 3.5, 4.8, and 7.1 dBA, respectively. At the blade passing frequency, the dominant upstream-propagating azimuthal acoustic modes were suppressed. Full-passage unsteady computational fluid dynamics calculations revealed that the duct transforms multiple suction vortices into a single annular vortex structure and weakens the interaction with the rotor blades. In addition, the acoustic analogy was used to compute the reduction of far-field noise and the variations in the major acoustic modes. This revealed a noise-reduction trend similar to that seen in the experiments. Essentially, the duct restrains the non-uniform inlet flow to influence the various inlet–rotor–stator interaction modes. The application of this approach to various fan configurations confirmed that a duct with a parameter of L/D (duct length/duct inner diameter) equal to 0.08 can be recommended as a compact and efficient way to reduce noise.

Flow characteristics and stability of induced shock waves in the isolator of rotating detonation ramjet under flight Mach number 2.5 conditions

A 3D numerical simulation of a rotating detonation ramjet engine (RDRE) with isolator and combustor was performed under flight Mach number 2.5 conditions. Factors that influence the stable operation of isolator, such as equivalence ratio, length and expansion ratio of the isolator, were systematically investigated. The structure and stability mechanism of shock wave in the isolator wave were also investigated. Results show that the shock waves in the isolator are mainly composed of the spiral shock wave band (SSWB) and the leading shock wave (LSW), which are induced by the detonation wave and the strong disturbance of SSWB in the supersonic incoming flow, respectively. The airflow behind the LSW obtains the total pressure gain caused by the work of SSWB, when SSWB moves toward the isolator inlet. The speed of LSW is mainly affected by the pressure of detonation wave. The greater the pressure of the detonation wave, the faster the speed of LSW. When the total pressure at the leading edge of SSWB is lower than that of the incoming flow, LSW will stabilize in the isolator. A concept of critical pressure ratio was proposed in the present study, which is the ratio of the average total pressure of the rotating detonation wave to the total pressure at the isolator inlet. In the research configuration and working conditions of this paper, the critical pressure ratio is slightly smaller than 6 when the equivalence ratio of H2/Air premixed mixture is 0.7, below which the isolator can work continuously and stably.

Experimental study on the aerodynamic performance of variable geometry low-pressure turbine adjustable guide vanes

An annular cascade testing rig of a variable-geometry low-pressure turbine with a large expansion angle was designed and built, combining a five-hole probe, a surface static pressure test system, and a PIV(Particle Image Velocimetry) measurement system. The effects of exit Mach numbers (0.2, 0.3, 0.4), turning angles (−1.5°, 0°, 3°), and adjustable device diameters (30 mm, 40 mm) on turbine cascade aerodynamic performance were experimentally investigated. Numerical simulations were also carried out to gain more insight into the flow fundamentals. Results show that the endwall clearance and the adjustable device significantly influence the flow field, with leakage flows before, after, and around the disc. The leakage vortex and passage vortex formation resulted in two high-loss regions in the shroud and hub endwall regions. The aerodynamic loss structures at the exit section were similar at different Mach numbers and varied considerably at different turning angles. Besides, a larger area of the adjustable device (d = 40 mm) was found to reduce the leakage loss caused by upper and lower clearance leakage flows and inhibit the development of secondary flows, resulting in a more straightforward secondary flow structure and a smaller influence range. Quantitatively, the adjustable device with a diameter of 40 mm could decrease the average total pressure loss coefficients by 11.5%, 16.6%, and 6.3% at three turning angles (−1.5°, 0°, 3°), respectively, compare to the adjustable device with a diameter of 30 mm.

Vibration and noise reduction of phononic crystal structure laid on the noise transmission path of axial piston pump

The radiated noise of an axial piston pump has been reduced previously by modifying shell structure. However, the effects of these methods of reducing vibration and noise are not clear. In this study, a noise reduction method that uses a phononic crystal structure on the vibration noise transmission path of a piston pump was developed. First, It was determined that the radiated noise frequency of the piston pump was the maximum peak frequency of the excavator field sound pressure level. A phononic crystal cell structure was designed based on the main noise peak frequency range of the axial piston pump. Comparing the vibration characteristics of the piston pump with and without the phononic crystal revealed that the vibration frequency of the piston pump can be significantly attenuated in the range of 409–1181.7 Hz. Finally, The average total sound pressure level of the external-field radiated noise of the axial piston pump was calculated based on the laid and non-laid phononic crystal structures. The results show that the average total sound pressure level amplitude decreases by 8.3 dB(A) in the frequency range of 0–1500 Hz. This study provides theoretical guidance for the design of an axial piston pump with low vibration and noise.

Numerical study of unsteady shock/mixing interaction in confined space

Unsteady shock wave enhancement is an effective technical approach to achieve air/fuel mixing under high speed and compressible conditions. However, unsteady shock/mixing interactions are always accompanied by complex wave structures, so the height of the combustion chamber will inevitably have a significant impact on shock waves and engine performance. In this regard, shock/mixing interactions in confined space are studied in this article by direct numerical simulation to investigate the effect of wall constraint on shock wave enhancement. Shock wave structure, total pressure loss, thickness of mixing layer, and turbulence intensity of flow field with different confinement degrees are calculated and compared. The results show that the unsteady shock wave can dramatically enhance the thickness of the mixing layer and the turbulence intensity, thus improving the mixing efficiency. In addition, as the wall constraint increases, the intensity of the shock wave and the total pressure loss increase; the flow field is more prone to Mach reflection. The average total pressure loss caused by steady shock wave and unsteady shock wave is essentially the same for an identical wall height, but the total pressure distortion caused by the unsteady shock wave is more substantial. Furthermore, the enhancements of mixing efficiency by the shock wave are also affected significantly by the degree of wall constraint; therefore, a suitable wall height needs to be determined in order to achieve the highest mixing efficiency.