Effect Of Inlet Flow Distortion Research Articles

Effects of Inlet S-duct on Inducer Performance and Cavitation Instability

To investigate the effect of inlet flow distortion on two-bladed inducer performance and cavitation instability, the s-shaped duct was installed at the inlet of the inducer to induce secondary flow. Inducer cavitation performance with and without s-duct were compared while varying the cavitation number. Also, the effect of s-duct on the occurrence of alternate blade cavitation was investigated using unsteady casing pressure measurement and high-speed camera visualization. It was shown that the s-duct decreases the strength of alternate blade cavitation and lowers the head breakdown cavitation number without considerable head loss by reducing the tip leakage vortex cavitation.

Investigation of inlet distortion effects on axial compressor performance based on streamline curvature method

In this paper, the effects of inlet flow distortion on performance maps and details of the flow field are investigated using the Streamline Curvature Method. The results are presented for both design and off-design conditions and compared with experimental data, which shows good agreement. The effects of inlet flow distortion are investigated by inlet total pressure variation in three different cases in the way that the average total pressure remains constant and equal to the design value. The results show that a relative increase in the total pressure at tip causes an increase in the pressure ratio and efficiency as well as a better performance in the choking region. Alternatively, a relative increase in the total pressure in hub causes opposite behavior and a better performance at the surging region.

Stability assessment of an airflow distorted military engine’s FAN

Military aircraft are often subjected to severe flight maneuvers with high angles of attack and angles of sideslip. These flight attitudes induce non-uniformity in flow conditions to their gas turbine engines, which may include distortion of inlet total pressure and total temperature at the aerodynamic interface plane. Operation of the downstream engine’s compression system may suffer reduced aerodynamic performance and stall margin, and increased blade stress levels. The present study presents a methodology of evaluating the effect of inlet flow distortion on the engine’s fan stability. The flow distortion examined was induced to the aerodynamic interface plane by means of changing the aircraft’s flight attitude. The study is based on the steady-state flow results from 27 different flight scenarios that have been simulated in computational fluid dynamics. As a baseline model geometry, an airframe inspired by the General Dynamics/LMAERO F-16 aircraft was chosen, which has been exposed to subsonic incoming airflow with varying direction resembling thus different aircraft flight attitudes. The results are focused on the total pressure distribution on the engine’s (aerodynamic interface plane) face and how this is manifested at the operation of the fan. Based on the results, it was concluded that the distorted conditions cause a shift of the surge line on the fan map, with the amount of shift to be directly related to the severity of these distorted conditions. The most severe flight attitude in terms of total pressure distortion, among the tested ones, caused about 7% surge margin depletion comparing to the undistorted value.

Study for the Effect of Combined Pressure and Temperature Distortion on a Turbojet Engine

This paper describes how the effect of inlet flow distortion to a turbojet can be evaluated by a distortion model of whole engine, which is based on mass, momentum and energy conservation, and has been proved to be a valid tool for evaluating the effects of inlet flow distortion on turbofan.In this model, pressure (or temperature) distortion is quantified with coefficient which associates the pressure (or temperature) in the spoiled sector with the value in the clean sector. Detailed computation and analysis under different overlap phase and distortion intensity are conducted on the stability of turbojet after the representation of combined distortion index. It can be concluded that there is a maximal loss of stall margin when total pressure distortion sector laps over total temperature distortion sector completely. The reduction of stall margin arising due to combined inlet distortions can be minimized through the optimization of a disturbance overlap phase.

Effects of Inlet Flow Distortion on the Performance of Aircraft Gas Turbines

This paper describes how the fundamental effects of inlet flow distortion on the performance of gas turbines can be evaluated with any engine performance program that employs an integrated parallel compressor model. In this simulation method, both pressure and temperature distortions are quantified with coefficients, which relate the pressure (respectively temperature) in the spoiled sector to the value in the clean sector. In single spool compressor engines, the static pressure at the exit of the clean sector equals that of the distorted sector. This hypothesis does not hold true with multispool compressor engines because the short intercompressor ducts, which often contain struts or vanes, do not allow the mass flow transfer over the sector borders, which would be required for balancing the static pressures. The degree of aerodynamic coupling of compressors in series can be described in the performance simulation program by the simple coupling factor introduced in this paper. There are two fundamentally different reasons for the change in engine performance: First, there is the impact of the flow distortion on the component efficiencies and thus the thermodynamic cycle and second there are performance changes due to the actions of the control system. From the engine system simulation results, it becomes clear why inlet flow distortion has only a minor impact on the thermodynamic cycle if the comparison of the two operating conditions (with clean and distorted inlet flow) is made at the properly averaged engine inlet conditions. For each compressor, the parallel compressor theory yields two operating points in the map, one for the clean sector and one for the spoiled sector. The performance loss due to the distortion is small since the efficiency values in the two sectors are only a bit lower than the efficiency at a comparable operating point with clean inlet flow. However, the control system of the engine can react to the inlet flow distortion in such a way that the thrust delivered changes significantly. This is particularly true if a compressor bleed valve or a variable area nozzle is opened to counteract compressor stability problems. Especially, using recirculating bleed air for increasing the surge margin of a compressor affects the performance of the engine negatively. Two examples show clearly that the pros and cons of recirculating bleed can only be judged with a full system simulation; looking at the surge line improvement alone can be misleading.

Effects of Inflow Distortion due to Hub Cap's Shape on the Performance of Axial Flow Fan

Performance characteristics of an axial flow fan having distorted inlet flow have been investigated using numerical analysis. Two kinds of hub-cap, rounded and right-angled front shape, are tested to investigate the effect of inlet flow distortion on the fan performance. In case of right-angled front shape, axisymmetric distorted inflow is induced by flow separation at the sharp edge of hub-cap, and the characteristics of the inflow depend on the distance between hub-cap and blade leading edge. Three-dimensional Reynolds-averaged Navier-Stokes equations are introduced to analyze the flow characteristics inside the blade passage. Numerical solutions are validated in comparison with experimental data measured by a five-hole probe downstream of the fan rotor. It is found from the numerical results that non-uniform axial inlet velocity profile near the hub results in the change of inlet flow angle. Large recirculation flow upstream the fan rotor for the right-angled hub-cap induces separated flow on the blade surfaces near the hub region, and thus deteriorates the performance of fan rotor. The effect of the distance between hub-cap and blade leading edge on the efficiency is also discussed.

허브 캡 형상에 따른 축류송풍기 성능특성

Performance characteristics of an axial flow fan having distorted inlet flow have been investigated using numerical analysis as well as experiment. Two kinds of hub-cap, rounded and right-angled front shape, are tested to investigate the effect of inlet flow distortion on the fan performance. Numerical solutions are validated in comparison with experimental data measured by a five-hole probe downstream of the fan rotor. It is found from the numerical results thatnon-uniform axial inlet velocity profile near the hub results in the change of inlet flow angle. Large recirculation flow upstream the fan rotor for the right-angled hub-cap induces a negative incidence, thus invokes separated flow on the blade surfaces and deteriorates the performance of fan rotor.

Effects of Inlet Flow Distortion on Cavitation Instability and Blade Stress Fluctuation in an Inducer

To investigate the effect of inlet flow distortion on cavitation instability, unsteady pressure and blade stress fluctuation were observed in a 3-bladed inducer. The inlet flow distortions were generated by using screens installed upstream of the inducer. In addition, the effect of the frequency of the fluctuation of the angle of attack caused by the inlet flow distortion was examined with three screens. The following results were obtained : (1) The present inlet flow distortions have almost no effect both on the pressure and cavitation performances. (2) The conventional and higher order rotating cavitations were suppressed by the present inlet flow distortion. However, the occurrence of the conventional cavitation surge was enhanced at lower cavitation number. (3) Amplitude of the blade stress fluctuation caused by the inlet flow distortion decreased with increasing of the frequency of the fluctuation of the angle of attack. (4) The phase difference between the blade stress fluctuation due to the inlet flow distortion and the fluctuation of the angle of attack increased as decreasing of the cavitation number.

Unsteady Stress of 4-Bladed Inducer Blades and the Effect of Inlet Flow Distortion.

Unsteady stress of 4-bladed inducer blades was measured with and without inlet flow distortion at the blade root near the leading edge. The following results were obtained : (1) Without the inlet flow distortion, and with the alternate blade cavitation at intermediate cavitation number, the mean stress of the blade with shorter cavity is lower than that with longer cavity. At lower cavitation number, the stress fluctuation occurs caused by the cavitation instabilities such as rotating cavitation and cavitation surge, which is one of the major causes of stress fluctuation of inducers. (2) The magnitude of stress fluctuation due to the interaction with the inlet flow distortion basically decreases as we decrease the cavitation number. With inlet flow distortion, the occurrence ranges of alternate blade cavitation and cavitation instability shift toward the lower cavitation number. Under the alternate blade cavitation, the fluctuation of longer cavity causes the stress fluctuation of the adjacent blade with shorter cavity. The stress fluctuations caused by the rotating cavitation and cavitation surge are neary the same level as those in case without inlet flow distortion.

Unsteady Stress of 4-Bladed Inducer Blades and the Effect of Inlet Flow Distortion

Unsteady stress of 4-bladed inducer blades was measured at the blade root near the leading edge with and without inlet flow distortion. The following results were obtained: (1) Without the inlet flow distortion, the mean stress of the blade with shorter cavity is smaller than that with longer cavity under the alternate blade cavitation at intermediate cavitation number. At lower cavitation number, the stress fluctuation occurs caused by the cavitation instability such as rotating cavitation/cavitation surge, which is one of the major causes of stress fluctuations in inducers. (2) The magnitude of the blade stress fluctuation due to the interaction with the inlet flow distortion basically decreases as we decrease cavitation number. With inlet flow distortion, the occurrence ranges of alternate blade cavitation and cavitation instabilities shift toward lower cavitation number. Under the alternate blade cavitation, the fluctuation of longer cavity causes the stress fluctuation of the adjacent blade with shorter cavity. The stress fluctuations caused by the rotating cavitation and cavitation surge are nearly the same level as those in case without inlet flow distortion

619 インデューサの入口偏流が非定常キャビテーションに与える影響(GS-5 流体機械(2))

To investigate the effect of inlet flow distortion on unsteady cavitation, experiments were carried out using a 4-bladed inducer was examined. The flow distortion was generated by the "screen A" with holes of uneven sizes. To examine the effect of existence of the screen, experiments were also made by using the "screen B" with uniform apertures. It was found that cavitation surge occurs more easily instead of rotating cavitation in the distortion flow. Cavity length oscillates with a phase difference to the variation of angle of attack due to the distortion

Education Committee Best Paper of 1996 Award: Response of a Turbofan Engine Compression System to Disturbed Inlet Conditions

A generic code DYNTECC has been adapted to perform a parametric study of the effect of inlet flow distortion on the stability of the Pratt and Whitney TF30 engine. This code was developed at Arnold Engineering Development Center, USA, for single and dual spool systems. It was modified at AMRL to accommodate the particular geometry of the TF30 engine. The stage characteristics needed to operate DYNTECC were derived from experimental data for the fan and low-pressure compressor. For the high-pressure compressor they were derived using the STGSTK code developed at NASA Lewis Research Center. This program was modified at AMRL to include real flow effects that were in turn derived using yet another adapted code, CASCAD. The code was primarily used at AMRL to predict the onset of system instability due to simulated full-face rapid inlet temperature ramps typical of those caused during armament firings. It was also run with sinusoidal total pressure oscillations of varying amplitudes and frequencies at the inlet. The code predictions were compared with available data whenever possible, and were found to be consistent with the observed experimental trends.

Effect of Inlet Flow Distortion on Performance of Vortex Controlled Diffusers

The present experimental investigations are concerned with diffusers employing the concept of vortex control to achieve high pressure recovery in a short length. Two types of two-dimensional diffusers have been studied, namely, vortex controlled and hybrid diffusers. Investigations have been carried out on such short diffusers with symmetrically and asymmetrically distorted inlet velocity profiles for area ratios 2.0 and 2.5 and divergence angle of 30 and 45 deg at a Reynolds number of 105. For each of the above configurations, experiments have been carried out for a range of fence subtended angles and bleed rates. The results indicate improvement in diffuser effectiveness up to a particular bleed off for both types of diffusers. It was observed that the nature of exit velocity profiles could be controlled by differential bleed.