Total Pressure Recovery Coefficient Research Articles

Flow Development Through An S-Shaped Diffusing Duct

Abstract This paper focuses on the internal flow development of an S-shaped diffusing duct. Based on the experimental result of total pressure recovery coefficient, the Reynolds stress model (RSM) was selected as a suitable turbulence model for the present study. The numerical results show that 6.2 times the area ratio of the exit to inlet and the aggressive deflection at the first bend of the lower wall lead to strong adverse pressure gradient and very large flow separation, and create a pair of counter-rotating vortices along streamwise direction. The duct diffuser efficiency is 72.37 %. The area-averaged total pressure recovery coefficient at the exit of the duct is 0.9814, and the synthesis distortion index DC (60) is 0.7081.

Aerodynamic optimization to tandem stators by using sweep and dihedral

In the modern aerodynamic design of turbomachinery blades, the geometries of blades often need to be reshaped to achieve better aerodynamic performance by introducing extra parametric design variables. A higher variable dimension will lead to a larger sampling range as well as a sparser sample distribution, which challenges the effectiveness and stability of optimization schemes based on surrogate model by making the model prediction quality even poorer. In this paper, a multi-objective optimization based on Gaussian process model was carried out for a high dimensional design space. Based on the previous two-dimensional optimization, tandem stators of a modern compressor were optimized by the design of sweep and dihedral. The purpose of the study is to improve the aerodynamic performance of the compressor tandem stators as well as to provide an effective optimization scheme for high dimensional multi-objective optimization problems. The design of sweep and dihedral for reshaping the tandem stators consists of a total of 18 design variables. An improvement in total pressure recovery coefficient of at least 0.7% at positive incidence and at least 0.3% at negative incidence was obtained, much larger than that in the previous two-dimensional optimization. The optimization process shows that, by using Gaussian process as the surrogate model and a special sampling strategy, this optimization scheme is effective and efficient to handle this high dimensional space. The aerodynamic influences of design parameters of tandem blades were analyzed in detail and the superiority of sweep and dihedral in reducing aerodynamic loss was confirmed.

Outlet Surface Area Influence in Spiral Casing Design on Centrifugal Fan Performance

In this paper, the effect of the outlet surface area of the spiral casing on the performance of a centrifugal fan was investigated using open source CFD software OpenFOAM [1]. An automized loop with RANS and data post-processing is set up using Matlab, for allowing a large number of parameter variations. The effect was analyzed as a function of total pressure loss and static pressure recovery coefficient and on total efficiency as well.

Outlet Surface Area Influence in Spiral Casing Design on Centrifugal Fan Performance

In this paper, the effect of the outlet surface area of the spiral casing on the performance of a centrifugal fan was investigated using open source CFD software OpenFOAM [1]. An automized loop with RANS and data post-processing is set up using Matlab, for allowing a large number of parameter variations. The effect was analyzed as a function of total pressure loss and static pressure recovery coefficient and on total efficiency as well.

Study on Inlet and Engine Integrated Model with Normal Shock Position Feedback

In order to consider the inlet and engine integrated model of supersonic airliner, the dynamic identification and control of inlet normal shock are studied. The research is based on the bleed air flow rate under supersonic conditions. With the two-dimensional CFD model of supersonic inlet, the dynamic and static effects of the bleeding flow rate on the normal shock position were investigated. The transfer function was identified, and simultaneously the paper carried out a comprehensive study of inlet and engine integrated model, which is established based on the inlet shock position model and engine component level model. The relationship between normal shock position and total pressure recovery coefficient has been taken into consideration in this model. Based on the inlet and engine integrated model, the closed-loop control simulation of normal shock position is carried out. The results show that the model could resist the disturbance of the inlet flow and keep the inlet and engine matching operation point stable near the optimal value.

Research on the coupled design method for the aerodynamic configuration of a mixed flow exhaust system with a confluent mixer

A confluent mixer-nozzle-shaped central plug coupled design method by using the B-spline, CFD method and revised particle swarm optimization is proposed in this paper. Then, this method is used to re-design a mixed flow exhaust system with a confluent mixer, and the performance of the re-designed model is compared with the exhaust system designed by the separated method. According to the comparison results, the re-designed exhaust system has a better mass flux distribution than the original system. The difference in bypass ratio between the re-designed model and theoretical design is 2.8%. With respect to aerodynamic performance, the thrust of the re-designed exhaust system is 6.1% higher than that of the original system under the design condition, and its total pressure recovery coefficient increases to 0.995 from 0.987 of the original model. At off-design conditions, the thrust and total pressure recovery coefficient of the re-designed model increase by 4.3% and 0.6%, respectively, compared with the original model.

Impacts of jet angle and jet-to-crossflow pressure ratio on the mixing augmentation mechanism in a shcramjet engine

Abstract The mixing process between the fuel and the incoming flow should be taken into consideration for the shock-induced combustion ramjet (shcramjet) engine, and this is pivotal for its successful engineering implementation. In the current study, the impacts of the gaseous fuel jet angle and the jet-to-crossflow pressure ratio are investigated numerically in order to make a foundational study and reveal the mixing augmentation mechanisms of different conditions. Flow fields windward and leeward are studied, and some parameters are provided to evaluate the flow field properties quantitatively, namely the mixing efficiency, the total pressure recovery coefficient, the fuel penetration depth and the mixing length. The obtained results predicted by the three-dimensional Reynolds-Averaged Navier-Stoke (RANS) equations coupled with the two equation shear stress transport (SST) k-ω turbulence model show that both the jet angle and the jet-to-crossflow pressure ratio have a great influence on the flow field, and the hydrogen distribution and streamwise vorticity downstream of the injectant orifice are affected seriously. The small jet angle and low jet-to-crossflow pressure ratio are more beneficial for the air-fuel mixing but with some shortcomings, and there needs an optimum result in the future to capture better achievement.

Numerical Study on Response Characteristics of Solid Rocket Pintle Motor

Pintle technology is currently a versatile technology used in a solid rocket motor (SRM) to control the desired thrust by changing the nozzle throat area, while effectively controlling the chamber pressure at the same time. The sudden movement of the pintle can induce rapid changes in the flow field and the occurrence of pressure oscillations inside the combustion chamber. The analysis of such rapid changes is essential to design an efficient controllable pintle rocket motor for a better thrust regulation. Two-dimensional axisymmetric models with mesh generation and required boundary condition were designed to analyze the effects of three different pintle head shape models in SRM thrust regulation effect. Dynamic mesh method was used with specific velocity for moving plug/pintle in the numerical analysis of SRM thrust regulation. The effects of different pintle head models on the flow field, combustion chamber pressure, mass-flow rate, thrust and Mach number were investigated. According to the analysis of total pressure response time, the simulation data revealed that circular pintle head model responded faster among three different models. According to the thrust effect, parabolic pintle has the maximum value of thrust and the greatest total pressure recovery coefficient among all pintle head models.

Parametric study on mixing augmentation mechanism induced by air injection in a shock-induced combustion ramjet engine

The fuel-air mixing process plays an important role in the shock-induced combustion ramjet (shcramjet) engine. In the current study, the investigation of front fuel jet and rear air jet is provided in order to study the mixing effect induced by the air jet and reveal the mixing augmentation mechanism and formation of several recirculation zones. Some parameters are also provided to evaluate the flow field properties quantitatively, namely the mixing efficiency, the total pressure recovery coefficient, the fuel penetration depth and the mixing length. The obtained results predicted by the three-dimensional Reynolds-average Navier-Stokes (RANS) equations coupled with the two equation shear stress transport (SST) k-ω turbulence model show that the additional air jet is really beneficial for accelerating the mixing process and improving the mixing efficiency. The shear vortex and air injected are the key sources for the mixing enhancement mechanism of the dual injection strategy. The formations of recirculation zones midstream and downstream are provided as well. The midstream recirculation zone “R2” is related to both front fuel jet and rear air jet, and “R3” is related to the air jet only. The downstream recirculation zone1 is composed by flows from the fuel jet and the air jet, and the downstream recirculation zone2 is formed by hydrogen flows.

URANS study of pulsed hydrogen jet characteristics and mixing enhancement in supersonic crossflow

In this paper, three-dimensional pulsed hydrogen jet in supersonic crossflow (PJISC) is investigated by the unsteady Reynolds Averaged Navier-Stokes (URANS) simulations with the k-ω shear stress transport (SST) turbulence model. The numerical validation and mesh resolution have been carried out against experiment firstly. The effects of the pulsed frequency and amplitude on the jet flow field and mixing performance in supersonic cross-flow are all addressed. It significantly changes the distribution of the hydrogen jet flow by comparing with the steady jet in supersonic crossflow. The fuel jet penetration, mixing efficiency, decay rate of the maximum hydrogen mass fraction and total pressure losses are used to quantitatively analyze the mixing performance. The mixing of fuel and incoming air flow is enhanced by the pulsed jet, especially for the case of 50 kHz, which is the optimal pulsed frequency while considering the effects of jet excitation frequency in the present simulations. The decay rate of the maximum mass fraction of hydrogen in the far field downstream is related to the frequency of the pulse jet. Moreover, the pulsed frequency and amplitude have little effects on the total pressure recovery coefficient for the cases studied in the present simulations.

Design method with controllable velocity direction at throat for inward-turning inlets

In the design of a hypersonic inward-turning inlet by applying the traditional basic flow-field, a reflected shock-wave is formed in the isolator due to the continuous reflection of the cowl-reflected shock wave in the basic flow-field, which interacts with the boundary layer to produce a considerable influence on the performance of the inlet. Here, a basic flow-field design method that can control the velocity direction at the throat section is developed, and numerical simulations are conducted to demonstrate the effectiveness of this method. The method presented in this paper can achieve the absorption of the reflected waves at the shoulder of the basic flow-field by adjusting the variation law of the center radius in the basic flow-field, and a smooth transition between the compression surface and the isolator can also be produced. The Mach number and total pressure recovery coefficient of the inlet designed according to this method are 3.00 and 0.657, respectively, at design point (the incoming flow Mach number Ma∞ = 6.0). The results show that with this method, the inlet can efficiently weaken both the reflection of the shock wave and the interaction between the boundary layer and the reflected shock waves, which improves the aerodynamic performance of the inlet.

Parametric Design Method and Performance Analysis of Double S-Shaped Nozzles

A parametric design method, which was based on super-elliptical transition and self-adaption infrared radiation shield for the double S-shaped nozzle, was introduced. The complete shielding of high-temperature components in the S-shaped nozzle was realized. Model experiments and numerical simulations were performed to investigate the effects of offset ratioS/D, the ratio of length to diameterL/D, and the aspect ratioW/Hon the aerodynamics and infrared radiation. The results showed that the total pressure recovery and thrust coefficients were improved initially, but dropped rapidly with the increase in offset ratios with the range of investigated parameters. There existed an optimal offset ratio for the aerodynamic performances. Considering the weight penalty, the length of nozzles should only be increased properly to achieve better aerodynamic performances. Both friction and viscous losses caused by large streamwise vortices dominated the aerodynamic performances of nozzles. The nozzle with the aspect ratio ofW/H=5.0was recommended for achieving optimal aerodynamics. The increase in aspect and offset ratios could effectively suppress plume radiation, which was, however, not sensitive to overall radiation. Compared to circular nozzles, double S-shaped nozzles reduced overall infrared radiation by over 50%, which proves significant stealth ability. A balance between aerodynamic performances and infrared radiation suppression could be reached for double S-shaped nozzles.

Reynolds-average Navier-Stokes study of steady and pulsed gaseous jets with different periods for the shock-induced combustion ramjet engine

The mixing process is very important for the shock-induced combustion ramjet engine. In the current study, the steady jet, as well as pulsed jets with different periods, is investigated in order to achieve adequate fuel/air mixing in the supersonic flow. Flow field properties are studied numerically based on grid independency analysis and code validation. The influence of the hydrogen distribution, as well as the flow field parameters such as mixing efficiency, total pressure recovery coefficient, and fuel penetration depth, is deeply analyzed for different jet-to-crossflow pressure ratios, namely, 10.29 and 25.15. The obtained results predicted by the three-dimensional Reynolds-averaged Navier-Stokes equations coupled with the two equation shear stress transport k-ω turbulence model show that the grid scale makes only a slight difference to wall pressure profiles. The pulsed jets with different periods are beneficial for the mixing process, especially when the jet-to-crossflow pressure ratio is high, and it has special advantages on reducing the total pressure loss and improving the fuel penetration depth. Among the pulsed jets considered in the current study, the T1 pulsed jet with higher frequency has the best performance, and its mixing augmentation mechanism is predicted. Its mixing enhancement mechanism is focusing on merging a mass of air around into the fuel core by the intermittent injection.

RANS study of steady and pulsed gaseous jets into a supersonic crossflow

The mixing process plays an important role in the combustion realization of the scramjet engine. In the current study, the steady jet, as well as pulsed jets with different wave shapes namely sine, square and triangle waves, is investigated in order to achieve adequate fuel/air mixing. Flow field properties are studied numerically based on grid independency analysis and code validation. The vortex structures, as well as the flow field parameters such as mixing efficiency, total pressure recovery coefficient, fuel penetration depth and mixing length, are deeply analyzed for different jet-to-crossflow pressure ratios. The obtained results predicted by the three-dimensional Reynolds-average Navier-Stokes (RANS) equations coupled with the two equation SST κ-ω turbulence model show that the grid scale makes only a slight difference to wall pressure profiles for all cases studied in this article. Compared with the steady jet, the pulsed jets with different wave shapes are beneficial for the mixing efficiency improving of the transverse jet, and the pulsed jets have special advantages on reducing the total pressure loss and mixing length but not for improving the fuel penetration depth. When the jet-to-crossflow pressure ratio is high, the performance of pulsed jets is better, and different wave shapes in the pulsed jet result in different vortex structures. This should be studied and discussed deeply in the near future.

Thermodynamic analysis of a solid oxide fuel cell jet hybrid engine for long-endurance unmanned air vehicles

The turbine-less jet engine is promising due to the compressor driven by a motor and the high combustor exit temperature. It is a key problem that how to provide electric power for the motor. In this paper, a novel solid oxide fuel cell (SOFC) jet hybrid engine with anode and cathode recirculation is proposed and investigated where the SOFC power system is instead of the turbine to provide power for the compressor. For the system, compressed air entering into SOFC cathode channel is preheated by cathode recirculation exhaust. The gases reform in the reformer, which are air, fuel and steam from the anode recirculation exhaust. Reformed gases are provided for the SOFC anode channel. SOFC produces electric power to drive the compressor by a motor. Then, SOFC exhaust enters the combustor. The combustor exhaust expands and produces propulsion power in the nozzle. In order to evaluate and improve the performance of the SOFC jet hybrid engine, the thermodynamic analysis model is built. The energy and exergy analysis are accomplished. The effect of pressure ratio and flight altitude on the performance of the hybrid engine are studied. In addition, sensitivity analysis is accomplished. The preliminary results are as follows: (1) The thermal efficiency, the specific thrust and the specific impulse of the engine could reach to 57.60%, 790.00 N/(kg⋅s−1) and 4132 s under design conditions. (2) The sum of the relative exergy destruction ratio of the SOFC, the combustor, the nozzle and the exhaust is over 85%. (3) The total pressure recovery coefficient of the SOFC has a strong influence on the performance of the SOFC jet hybrid engine.

Numerical Study on Internal flow Field Dynamic Performance of Scramjet

The pressure pulsation caused by the combustion of the combustion chamber of the scramjet engine has a great influence on the flow and performance of the inlet. Although the isolation section prevents the propagation of this pressure pulsation, the pressure pulsation still flows to the inlet flow field. And performance has an adverse effect. In this paper, a method for calculating the dynamic performance parameters of the inlet is discussed. The influence of the pulsating pressure of the combustion chamber on the performance of the inlet is preliminarily studied. The influence law of different forms of back pressure pulsation on the flow coefficient and the total pressure recovery coefficient is obtained. Different back pressure pulsation forms have a great influence on the flow coefficient. The faster the response, the more obvious the change of the flow coefficient. The larger the reduction, the more likely the inlet channel will not start. Different back pressure pulsations have little effect on the total pressure recovery coefficient. In the design of the intake port, the influence of the back pressure pulsation on the performance of the intake port should be fully taken into consideration, and measures should be taken to prevent the performance of the intake port from being affected by the back pressure pulsation.

Study on Three-Dimensional Inner Flow Field Characteristics and Performance of Scramjet

The three-dimensional characteristics and performance of the flow field in the inlet of the scramjet engine were numerically simulated by CFD software. The flow characteristics in the width direction of the inlet and the influence of the aspect ratio on the performance of the inlet were studied. The calculation results show that the inlet flow has obvious three-dimensional characteristics, and the flow field structure is different in the width direction from the middle symmetrical section to the side wall surface, the Mach number is smaller and smaller, the static pressure is lower and lower, and the static temperature is higher, the greater the total pressure. The aspect ratio has little effect on the Mach number and static temperature of the outlet section of the inlet, but it has a great influence on the static pressure and total pressure. Within a reasonable range, the aspect ratio is doubled, the static pressure is increased by about 40%, and the total pressure is increased by about 84%. The inlet flow coefficient and the total pressure recovery coefficient increase as the aspect ratio increases. Within a reasonable range, the aspect ratio is doubled, the inlet flow coefficient is increased by approximately 53%, and the total pressure recovery coefficient is increased by approximately 83%.

Numerical Simulation on Rigid Foreign Object Exclusion in the Turboprop Engine Intake System With a Bypass Duct

By considering the exclusion characteristics of foreign objects in a new intake system with a bypass duct for turboprop engines, two kinds of common rigid foreign objects, the grains, and metal pieces, are modeled based on airworthiness standards and reference reports. On the assumption that only a perfect elastic collision occurs without any structural damage to the objects or intake walls, a numerical method based on single high-fidelity computational fluid dynamics (CFD) and dynamic unstructured mesh techniques to simulate the 6DOF motion and impacts of the rigid foreign objects is presented. A practical used intake system with a bypass duct is employed to validate the method. According to the tolerance size of the intake, two spherical grains with the radius of 0.037 m and 0.0555 m and a regular hexahedron aluminum metal piece with the dimension of 0.20 m×0.11 m×0.01 m are built to test the exclusion ability of the intake and analyze their effects on the intake performance. The simulation results indicate that, in the cases of a symmetrical flow field, geometry, and initial states, all the rigid foreign objects will move in the intake without lateral motions. The spherical grains without an initial angular velocity only translate in the intake, and the small one finally enters into the bypass duct after four impacts, while the larger one flies into the inner part of the engine after six impacts. The larger grain can lead to a more apparent loss on the intake performance due to the greater shielding effect on the flow field, and the maximum decrements of the total pressure recovery coefficient and mass flow can reach to 2% and 4.1%, respectively; the total pressure distortion rate increases 116%. A coupled motion of translation and rotation occurs for the regular hexahedron aluminum piece, and after four impacts on the intake, it finally excludes to the outer space of the nacelles from the bypass duct. Compared to the spherical grains, the aluminum piece has more significant actions on the intake performance. The maximum losses of the total pressure recovery coefficient and mass flow can be 2.3% and 1.54%, respectively, while the distortion rate increases 518%. Although the numerical method in this study is simple and ideal, it can help researchers to obtain quick and effective evaluation results in the initial design stage of the new intake system with a bypass duct for the turboprop engine to improve the design efficiency and level.

Effects of the aerothermoelastic deformation on the performance of the three-dimensional hypersonic inlet

The hypersonic inlet is more prone to deform when simultaneously subjected to aerodynamic load and harsh aerothermodynamic load. Moreover, the flow field of the hypersonic inlet is sensitive to configuration. Therefore, it is necessary to investigate the effects of the aerothermoelastic deformation on the flow structure and the performance of the hypersonic inlet. This study develops a loose coupling static aerothermoelastic analysis framework based on the CFD/CSD coupling method, and the one-way and the two-way aerothermal-aeroelastic coupling are both used in the analysis. Furthermore, the effects of the aerothermoelastic deformation on the flow structure and the performance of a three-dimensional hypersonic inlet are studied in detail. The reliabilities of the CFD method and the CFD/CSD coupling method are verified by the validation cases of DLR hypersonic inlet experimental model and the HIRENASD experimental model. The results obtained by the coupling methods are similar. However, the aerothermoelastic deformation obtained through the two-way coupling method is relatively larger, and the effects of the deformation on the inlet performance are more obvious. The maximum of the aerothermoelastic deformation exists at the leading edge of the inlet lip. The deformation changes the shock wave structure near the lip, strengthens the shock wave intensity inside the inlet, increases the length of the separated region and the temperature of the external wall, and changes the flow field of the exit. The aerothermoelastic deformation will lead to the increasing of the mass flow coefficient and the pressure rise ratio; however, it will decrease the total pressure recovery coefficient.

Preliminary experimental study on solid rocket fuel gas scramjet

In this paper, a new scramjet configuration using solid fuel as propellant is proposed, namely, the solid rocket fuel gas scramjet. The ignition and combustion characteristics and performance of the engine were evaluated by the experimental and numerical methods. The experiment simulated a flight environment of Mach 5.3 at a 21 km altitude. Solid oxygen-poor propellant containing boron was used in this study. The experiment results show that primary rich fuel gas can be reliably ignited in the supersonic combustor and can maintain stable combustion, which demonstrates the feasibility of the solid rocket fuel gas scramjet configuration. The numerical simulation results show that the combustion efficiency of the combustor is 0.56 and the total pressure recovery coefficient is 0.44, which further demonstrates the feasibility of the solid rocket fuel gas scramjet configuration proposed in this paper.