Inlet Flow Field Research Articles

Discretized Miller approach to assess effects on boundary layer ingestion induced distortion

The performance of propulsion configurations with boundary layer ingestion (BLI) is affected to a large extent by the level of distortion in the inlet flow field. Through flow methods and parallel compressor have been used in the past to calculate the effects of this aerodynamic integration issue on the fan performance; however high-fidelity through flow methods are computationally expensive, which limits their use at preliminary design stage. On the other hand, parallel compressor has been developed to assess only circumferential distortion. This paper introduces a discretized semi-empirical performance method, which uses empirical correlations for blade and performance calculations. This tool discretizes the inlet region in radial and circumferential directions enabling the assessment of deterioration in fan performance caused by the combined effect of both distortion patterns. This paper initially studies the accuracy and suitability of the semi-empirical discretized method by comparing its predictions with CFD and experimental data for a baseline case working under distorted and undistorted conditions. Then a test case is examined, which corresponds to the propulsor fan of a distributed propulsion system with BLI. The results obtained from the validation study show a good agreement with the experimental and CFD results under design point conditions.

Strip distortion generator for simulating inlet flow distortion in gas turbine engine ground test facilities

A methodology has been developed to generate a non-uniform/distorted inlet flow field to test a gas turbine engine in ground test facilities. The distorted flow field is generated by positioning radial and circumferential strips of varying widths upstream of the Aerodynamic Interface Plane. The interacting wakes from these strips are used to generate a given target flow field. The approximate superposition of these wakes is investigated and used to construct the strip arrangement which is subsequently validated by computing the flow field by solving the Navier–Stokes equations. The strip geometry designed using the present methodology is able to produce the target Mach number distribution with a root-mean-square error of 5.06%.

Experimental Investigation of Sidewall Compression and Internal Contraction in a Scramjet Inlet

In this paper, we present the results of an extensive measurement campaign to investigate the effects of external and internal sidewall compression and the variation of internal contraction on the performance and flowfield of a scramjet inlet. Experiments were conducted in the H2K wind tunnel of DLR, German Aerospace Center, in Cologne, Germany, at Mach 7. The performance was evaluated by static and total pressure ratios, kinetic energy efficiency, and mass capture ratios. The flowfield was analyzed using wall pressure distributions, pitot pressure, and Mach number profiles at the isolator interface to the combustion chamber and infrared thermography on the external ramps. The results show that the combination of a two-ramp inlet with external sidewall compression is not suitable for increasing the inlet’s compression capability as it induces strong separation and vortex structures in the external part, which strongly increase spillage and impair the starting behavior. Thus, no significant increases in internal contraction are possible, which inhibits any gains in the performance of the inlet. With internal sidewall compression, strong increases of the pressure ratio can be achieved at the cost of total pressure losses. With internal sidewall compression as well as without sidewall compression, the inlet is still self-starting at internal contraction ratios well above the Kantrowitz limit.

Investigation on the influence of jetting equipment on the characteristics of centrifugal pump

To reduce radial noises from the motor of centrifugal pumps, this study designed a water cooling system called jetting equipment to replace traditional fan cooling systems in pump motors. By measuring radiated noises, head, efficiency, and cavitation performance, the research compared the differences among experimental results of the original pump unit, the one with a normal design jetting pipe and another one with a larger jetting pipe. Results show that the radiated sound pressure level of the model pump was significantly reduced by 8.3 dB after integrating the jetting pipe. With a normal jetting pipe, no significant changes were observed in the head, efficiency, and shaft power curves, and cavitation performance improved under small flow rate. However, the performance with the larger jetting pipe worsened, except the hump phenomenon of the model pump under a small flow rate was enhanced. Computational fluid dynamics method was used to calculate the internal flow of three model pumps in order to investigate the jetting flow effect. A comparison among the flow fields at the inlet of the three types of pumps indicated that high-pressure water injection can effectively control inlet recirculation and improve velocity distribution in the inlet flow field with decreased recirculation vortex strength and recirculation onset critical flow rate.

Scaling Three-Dimensional Low-Pressure Turbine Blades for Low-Speed Testing

The present activity was carried out in the framework of the Clean Sky European Research Project ITURB (optimal high-lift turbine blade aeromechanical design), aimed at designing and validating a turbine blade for a geared open-rotor engine. A cold-flow, large-scale, low-speed (LS) rig was built in order to investigate and validate new design criteria, providing reliable and detailed results while containing costs. This paper presents the design of an LS stage and describes a general procedure that allows to scale three-dimensional (3D) blades for LS testing. The design of the stator row was aimed at matching the test-rig inlet conditions and at providing the proper inlet flow field to the blade row. The rotor row was redesigned in order to match the performance of the high-speed (HS) configuration, compensating for both the compressibility effects and different turbine flow paths. The proposed scaling procedure is based on the matching of the 3D blade loading distribution between the real engine environment and the LS facility one, which leads to a comparable behavior of the boundary layer and hence to comparable profile losses. To this end, the datum blade is parameterized, and a neural-network-based methodology is exploited to guide an optimization process based on 3D Reynolds-averaged Navier–Stokes (RANS) computations. The LS stage performance was investigated over a range of Reynolds numbers characteristic of modern low-pressure turbines (LPTs) by using a multi-equation, transition-sensitive, turbulence model. Some comparisons with experimental data available within the project finally proved the effectiveness of the proposed scaling procedure.

Vane Clocking Effects on Stator Suction Side Boundary Layers in a Multistage Compressor

The stator inlet flow field in a multistage compressor varies in the pitchwise direction due to upstream vane wakes and how those wakes interact with the upstream rotor tip leakage flows. If successive vane rows have the same count, then vane clocking can be used to position the downstream vane in the optimum circumferential position for minimum vane loss. This paper explores vane clocking effects on the suction side vane boundary layer development by measuring the quasi-wall shear stress on the downstream vane at three spanwise locations. Comparisons between the boundary layer transition on Stator 1 and Stator 2 are made to emphasize the impact of rotor-rotor interactions which are not present for Stator 1 and yet contribute significantly to transition on Stator 2. Vane clocking can move the boundary layer transition in the path between the wakes by up to 24% of the suction side length at midspan by altering the influence of the Rotor 1 wakes in the 3/rev modulation from rotor-rotor interactions. The boundary layer near the vane hub and tip experiences earlier transition and separation due to interactions with the secondary flows along the shrouded endwalls. Flow visualization and Stator 2 wakes support the shear stress results.

A computational study on the influence of a bleed slot on the flowfield of a bump-type inlet

The characteristics of a supersonic bump-type inlet with a bleeding system were numerically studied to examine the influence of boundary-layer bleeding in controlling shock wave/boundary layer interactions. The bump-type inlet, which is based on a conventional ramp-type inlet, was designed for two oblique shock waves and a terminal normal shock wave followed by a subsonic diffuser. A bleed slot connected to a plenum chamber was installed under the root of the normal shock wave. As a consequence, the bleeding mass flow extracted from the main inlet stream to the plenum chamber was controlled. The numerical simulations conducted in this study showed that the bleed slot could enhance the performance of the bump-type inlet.

Design methodology for shape transition inlets based on constant contraction of discrete streamtubes

In this paper we propose a design concept, i.e. constant contraction of discrete streamtubes, to develop a new design method for hypersonic inlets with shape transition, which enables the shape transition inlet to have high compression efficiency while keeping flow uniformity as much as possible. The method first divides the 3D flow field of the inlet into several groups of discrete streamtubes with constant contraction ratio. The axisymmetric flow within each stream tube is then optimized via computational fluid dynamics to have high compression efficiency, and these discrete streamtube groups are finally assembled together by matching their shock wave reflection positions to form a 3D inlet flow field with weak crossflow. This method can be used for the design of shape transition inlets with specified entrance/exit sections. To validate the present methodology, we design a rectangular-to-circular inlet with a design point of Ma 6 and a takeover point of Ma 4, and examine numerically the flow structure and the inlet performances.

Numerical validation and back-pressure effect on internal compression flows of typical supersonic inlet

AbstractA numerical study was conducted to analyse the performance of different turbulence models and different turbulence intensities and turbulence length scales specified for the boundary condition of the inflow to the internal compression flow field of a typical supersonic inlet. The effect of the back-pressure ratio on the properties of the flow field was also investigated. Computational results obtained by the commercial software FLUENT, which is used to solve the full two-dimensional Reynolds-averaged Navier-Stokes equations, were validated through both graphical and quantitative comparisons with previously published experimental data. The two-equation models that were considered in this study are the RNGk-ε, realisablek-ε, standardk-ε, and SSTk-ω turbulence models. The RNGk-ε model had the best performance among the four models and predicted good wall pressure distributions. The best agreement between the predicted results and experimental data was obtained when either the default values of the freestream turbulence intensity and length scale in the FLUENT solver were used, or the empirical formula was used to calculate the two parameters of the freestream turbulence properties. The shock wave pattern varied between the oblique mode and the fully developed normal mode with increasing back-pressure ratio, and the unstart phenomenon occurred when the back-pressure ratio was sufficiently high.

Simulation of axisymmetric scramjet inlet flow fields using anti-diffusive WENO Navier-Stokes solver

This study is based on the theory of gas dynamics and uses the Navier-Stokes equations as the governing equations to solve the hypersonic flow problems of the scramjet. For the turbulent flow, we use the Spalart-Allmaras one equation turbulence model, which produces better results for near wall and boundary layer flow field problems. The lower-upper symmetric Gauss-Seidel implicit scheme, which enables results to converge efficiently under steady state conditions, is combined with the anti-diffusive weighted essentially nonoscillatory (WENO) scheme to yield an accurate and efficient simulation tool for an axisymmetric scramjet flow field analysis. Using the WENO scheme’s high-order accuracy and its non-oscillatory solution at discontinuous regions, we can solve the hypersonic flow problems involving complex shock-shock/shock-boundary layer interactions inside the flow path. This simulation procedure is first verified against two existing partial examples to ensure its accuracy, and is then applied to a complete scramjet model with different initial conditions for a full flow field analysis. The aerodynamic data of Mach number, density, static temperature and pressure are obtained and the results discussed. The anti-diffusive WENO scheme produces more accurate resolution of shock and slip lines and their complex multiple interactions than other numerical approaches. This is of crucial importance for the scramjet complete flow field analysis as multiple shock-boundary layer and discontinuities interactions often occur within the long flow path.

Pressure Drop of Annular Flow Channel Electromagnetic Pump Examined Using Divided Flow Channel Model

It has been reported that operating an annular flow channel electromagnetic pump (EMP) near the peak of the head pressure and flow rate curve sometimes suffers a drop of head pressure. This phenomenon was attributed to nonuniform distribution of inlet flow or magnetic field, but its mechanism has not been clarified. For fear of this undesired head pressure drop, current EMP design is sometimes too conservative in that the rated efficiency is set low compared with experimentally achieved values. Understanding this phenomenon clearly, therefore, will prospectively make possible more proper design. We modeled the annular channel with parallel divided channels to examine the response of the EMP for distributed inlet flow. For each of the divided channels, the equation of fluid motion is numerically solved including the pressure from the external flow loop. Since the time constant of the pressure from the external loop is slow compared with that of the divided channels, decreased flow in some divided channels can undergo reversed pressure and become unstable in certain cases. Transient behaviors, such as the total head pressure and the flow rate of the EMP, were examined, and conditions of this pressure drop occurrence were clarified, making possible more proper EMP design.

Numerical Analysis of Effect of Boundary Layer Characteristics on the Flow Field in S-shaped Inlet

In order to explore the effect of boundary layer thickness and pressure gradient on the perfor- mance of the flow field in the inlet, we design a high offset rate S-shaped inlet based on a certain unmanned aeri- al vehicle (UAV), and its author has analyzed the effect of boundary layer characteristics on the inlet with nu- merical simulation method. The suction of boundary layer which leads to separation zone not only becomes longer in the inlet, but also moves to the center plane of symmetry, the separation point of boundary layer ap- pears in advance as pressure gradient increases. Considering the influence of the boundary layer, various perfor- mance parameters all exceeds that of the uniform entrance inlet conditions, especially the circumferential total pressure distortion of outlet increased by 58.2% at most, obviously can't meet the engine to work properly, so we must consider and pay attention to the effect of the boundary layer characteristics on the flow field in the S-shaped inlet.

Effect of blade sweep on inlet flow in axial compressor cascades

This paper presents comparative numerical studies to investigate the effects of blade sweep on inlet flow in axial compressor cascades. A series of swept and straight cascades was modeled in order to obtain a general understanding of the inlet flow field that is induced by sweep. A computational fluid dynamics (CFD) package was used to simulate the cascades and obtain the required three-dimensional (3D) flow parameters. A circumferentially averaged method was introduced which provided the circumferential fluctuation (CF) terms in the momentum equation. A program for data reduction was conducted to obtain a circumferentially averaged flow field. The influences of the inlet flow fields of the cascades were studied and spanwise distributions of each term in the momentum equation were analyzed. The results indicate that blade sweep does affect inlet radial equilibrium. The characteristic of radial fluid transfer is changed and thus influencing the axial velocity distributions. The inlet flow field varies mainly due to the combined effect of the radial pressure gradient and the CF component. The axial velocity varies consistently with the incidence variation induced by the sweep, as observed in the previous literature. In addition, factors that might influence the radial equilibrium such as blade camber angles, solidity and the effect of the distance from the leading edge are also taken into consideration and comparatively analyzed.

Effect of Inlet Geometry on Fan Performance and Inlet Flow Fields in a Semi-opened Axial Fan

Abstract In order to clarify the effect of inlet bellmouth size of semi-opened type axial fan on its performance and flow fields around rotor, fan test and flow field measurements using hotwire anemometer were carried out for 6 kinds of bellmouth size. As results of fan test, the shaft power curve hardly changed, even if the bellmouth size changed. On the other hand, the pressure-rise near best efficiency point became small with the bellmouth size decreasing. Therefore, the value of maximum efficiency became small as the bellmouth size decreased. As results of flow field measurements at fan inlet, the main flow region with large meridional velocity existed near blade tip when the bellmouth size was large. As bellmouth size became smaller, the meridional velocity at fan inlet became smaller and the one at outside of blade tip became larger. As results of flow field measurements at fan outlet, the main flow region existed near rotor hub side.

A Numerical Study on the Effect of Bleed System on Starting Ability and Flow Performance of Rampressor Inlet

A unique supersonic compressor rotor with high pressure ratio, termed the Rampressor, is presented by Ramgen Power Systems, Inc., (RPS). Based on the models of Rampressor inlet, the inlet flow field with bleed system is numerically studied. Validation of the employed computational fluid dynamics (CFD) scheme is provided through test cases. The effects of boundary layer bleed location and bleed amount on Rampressor rotor inlet start and flow performance are analyzed. The results indicate that the boundary layer bleed has a significant effect for start and flow performance of Rampressor inlet. Boundary layer bleed technique has been applied to eliminate the emerging flow separation zone for enhancing Rampressor rotor inlet performance and enlarging its stable working range. The starting ability and flow performance of Rampressor inlet are efficiently improved by bleeding system, but the improvement effect is different for Rampressor inlet with different bleed location. Along the position of bleeding system moves forward, the range of Rampressor inlet normal work rotation speed is enlarged. The flow performance of Rampressor inlet improves obviously with the increment of bleed flow rate, and exit stability of Rampressor inlet enhances. And in the same back pressure work condition of Rampressor inlet, bleed system has been shown to be effective that exit stability of Rampressor inlet ameliorates, but the loss of compressed air from the bleed system has a negative effect on overall Rampressor inlet efficiency.

Erratum: “Low-Speed Model Testing Studies for an Exit Stage of High Pressure Compressor” [ASME Journal of Engineering for Gas Turbines and Power, 2014, 136(11), p. 112603, DOI: 10.1115/1.4027637

In the Inlet Flow Field subsection of the Results and Discussion section, the blockage factor values of “0.12” and “0.115” should be replaced by “0.93” and “0.9315” respectively, in consideration of the general definition of blockage factor. The text is revised as:…of blockage factor for HPC exit stage is 0.93. By various numerical attempts, the length of the inlet duct between cowling end and compressor inlet is determined, which is equal to 0.8 m, and the measured result show that the blockage factor for design operating point is 0.9315, which agrees very well with the design value. It…Due to the same reason, the boundary layer parameter values of “3.23,” “3.28,” “3.96” and “3.16” are to be replaced by “3.05,” “3.11,” “2.25” and “1.86” respectively, in Table 2 on page 5. The revised table is below:Figures 12 and 13 on page 6 of the original manuscript contain some errors. The correct figures are as follows:

Conformal s-Shaped Inlet Design and Flow Field Characteristics of Flying Wing Unmanned Aerial Vehicle

According to the stealth and conformal requirement of flying wing UAV(Unmanned Aerial Vehicle),an dorsal subsonic S-shaped inlet with long diffuser and large offset is designed. In the light of the characteristics of the inlet, new area distribution is created. In the study, the model with power system and the other model whose pipeline connected are established. The coupled numerical simulation is also carried out on the inflow/outflow integrated for flying wing UAV, and it is applied to study the longitudinal aerodynamic performance of UAV and the flow characteristics of inlet under different flight conditions. Results indicate: The longitudinal aerodynamic performance of the model with power system is close to the model with pipeline connected, but the moment characteristic of the former is better; The inlet characteristics are similar when Ma=0.5 and Ma=0.6; As the mach number increasing, the inlet performance decreases rapidly, Especially at the Ma = 0.7, there is a large low-pressure dominated region at the small angle of attack α = 2°, which leads to the total pressure recovery coefficient decreasing rapidly and the flow distortion increasing obviously.

Flow over a heated block in a vertical channel

Purpose – The heat transfer rates from the body to the working fluid can be improved through altering geometric configurations of the body and its arrangement in the flow system. One of the arrangements for this purpose is to locate the body at the channel inlet while the convection current opposes it. Since the flow field in the channel inlet influences the heat transfer rates, changing the aspect ratio and inclination of the body is expected to modify the flow field while enhancing the heat transfer rates. Consequently, investigation into the influence of the aspect ratios and tilting angles of the body on the heat transfer rates in the channel flow becomes essential. The paper aims to discuss these issues. Design/methodology/approach – Numerical simulation of flow in a channel with the presence of solid block is carried out. The block aspect ratio is changed while keeping the area of the block constant for all aspect ratios. The tilting angle is also incorporated analysis to examine its effect on the Nusselt number. Findings – The throttling effect of the block at channel inlet accelerates the flow between the channel wall and the block faces. This, in turn modifies the thermal boundary layer around the block. In this case, heat transfer rates increase considerably at the block faces where the flow acceleration suppresses the thermal boundary layer thickness. This is more pronounced for large block tilting angles. The Nusselt number attains low values for the block face opposing to the flow at the channel inlet and the back face of the block. This is attributed to the mixing of the thermal current emanating from the side faces of the block in the region close to the back surface. In this case, thermal boundary layer thickens and the heat transfer rates from the block reduce significantly. The Nusselt number improves with reducing the block aspect ratio, which is particularly true along the side faces of the block. In addition, the influence of the block tilting angle on the Nusselt number is considerable for the low block aspect ratios. Research limitations/implications – The model study is validated with the previous studies for the drag coefficient. The study covers all the aspects of the flow situations and discusses the resulting fluid field and the heat transfer rates from the block. Practical implications – It is an interesting work for cooling applications. The block aspect ratio and its tilting angle in the channel influence considerably the flow field and the Nusselt number variation around the block faces. Social implications – The cooling technology may be improved through implementing the findings of the current work. Originality/value – It is an original work and it has never been submitted to other journals.

Numerical Analysis of the Turbine 99 Draft Tube Flow Field Provoked by Redesigned Inlet Velocity Profiles.

In recent years, several investigations on hydraulic turbine draft tube performance have shown that the hydrodynamic flow field at the runner outlet determines the diffuser efficiency affecting the overall performance of the turbine. This flow field, for which the principal characteristics are the flow rate and the inlet swirling flow intensity, is mostly developed on turbines designed for low head (high specific velocity) and operated away from their best efficiency point. To identify factors of the flow field responsible for loosing draft- tube efficiency, the correlations between the flow pattern along the diffuser and both swirl intensity and flow rate have been examined. An analytical representation of inlet flow field has been manipulated by a Multi Island Genetic Algorithm through the automatic coupling of multidisciplinary commercial software systems in order to obtain redesigned inlet velocity profiles. This loop allowed determining the profile for which the minimum energy loss factor was reached. With different flow field patterns obtained during the optimization process it was possible to undertake a qualitative and quantitative analysis which has helped to understand how to suppress or at least mitigate undesirable draft tube flow characteristics. The direct correlation between the runner blade design and the kinematics of the swirl at the draft tube inlet should suppose the perfect coupling at the runner-draft tube interface without compromising the overall flow stability of the machine.

A Numerical Study for Flow Excitation and Performance of Rampressor Inlet considering Rotor Motion

A unique supersonic compressor rotor with high pressure ratio, termed the Rampressor, is presented by Ramgen Power Systems, Inc. (RPS). In order to obtain the excitation characteristic and performance of Rampressor inlet flow field under external excitation, compression inlet flow of Rampressor is studied with considering Rampressor rotor whirling. Flow excitation characteristics and performance of Rampressor inlet are analyzed under different frequency and amplitude of Rampressor rotor whirling. The results indicate that the rotor whirling has a significant effect for flow excitation characteristics and performance of Rampressor inlet. The effect of rotor whirling on the different inlet location excitation has a definite phase difference. Inlet excitation becomes more complex along with the inlet flow path. More frequency components appear in the excitation spectrum of Rampressor inlet with considering Rampressor rotor whirling. The main frequency component is the fundamental frequency, which is caused by the rotor whirling. Besides the fundamental frequency, the double frequency components are generated due to the coupling between inlet compression flow of Rampressor rotor and rotor whirling, especially in the subsonic diffuser of Rampressor rotor inlet. With the increment of rotor whirling frequency and whirling amplitude, the complexity of Rampressor inlet excitation increases, and the stability of Rampressor inlet performance deteriorates.