Rotor Design to Attenuate Flow Distortion—Part II: An Unsteady Thin Airfoil Cascade Analysis

1975 ◽  
Vol 97 (1) ◽  
pp. 37-46
Author(s):  
C. T. Savell ◽  
W. R. Wells
Keyword(s):  
Physical Interpretation ◽  
Wave Length ◽  
Design Parameters ◽  
Flow Distortion ◽  
Inlet Distortion ◽  
Actuator Disk ◽  
Rotor Design ◽  
Thin Airfoil ◽  
Cascade Analysis ◽  
Airfoil Cascade

The transfer of stationary circumferential inlet distortion through a rotor is analyzed using unsteady thin airfoil cascade theory which can account for the distortion wave length, rotor chord and cascade solidity. The model consists of representing each blade by a moving doublet filament of finite length immersed in a compressible stream containing a velocity distortion. The study is limited to an unloaded, flat plate rotor. This model provides a new physical interpretation for the flow adjustments observed ahead of the rotor and for the generation of sound when an inlet distortion is imposed. The analytical results show the influence of solidity and other rotor design parameters on the distortion transfer. They are found to approach the semi-actuator disk results as the solidity tends to infinity.

Rotor Design to Attenuate Flow Distortion—Part I: A Semiactuator Disk Analysis

1975 ◽  
Vol 97 (1) ◽  
pp. 11-20 ◽  
Author(s):  
C. T. Savell ◽  
W. R. Wells
Keyword(s):  
Wave Length ◽  
Design Parameters ◽  
Transmission Characteristics ◽  
Flow Distortion ◽  
One Dimensional ◽  
Inlet Distortion ◽  
Rotor Design ◽  
Blade Cascade ◽  
Wave Guides ◽  
Parametric Studies

The transfer of stationary circumferential inlet distortion through a rotor is analyzed using unsteady semiactuator disk cascade theory. This method models the blade cascade as one-dimensional wave guides and describes the transmission characteristics of a rotor to be a function of the distortion wave length and the length of the rotor chord, as well as the normal design parameters. Two parametric studies on the response of a loaded rotor to inlet distortions are done for a single rotor operating at off design conditions and a number of rotors operating at their design points. Fourier series representations of arbitrary distortion wave shapes are used for comparison with experimental data.

Blade Forcing Function and Aerodynamic Work Measurements in a High Speed Centrifugal Compressor With Inlet Distortion

2009 ◽  
Author(s):  
Albert Kammerer ◽  
Reza S. Abhari
Keyword(s):  
Failure Modes ◽  
Pressure Sensors ◽  
Forced Response ◽  
Blade Surface ◽  
Centrifugal Compressors ◽  
Flow Distortion ◽  
Unsteady Pressure ◽  
Inlet Distortion ◽  
Forcing Function ◽  
Work Distribution

Centrifugal compressors operating at varying rotational speeds, such as in helicopters or turbochargers, can experience forced response failure modes. The response of the compressors can be triggered by aerodynamic flow non-uniformities, such as with diffuser-impeller interaction or with inlet distortions. The work presented here addresses experimental investigations of forced response in centrifugal compressors with inlet distortions. This research is part of an ongoing effort to develop related experimental techniques and to provide data for validation of computational tools. In this work measurements of blade surface pressure and aerodynamic work distribution were addressed. A series of pressure sensors were designed and installed on rotating impeller blades and simultaneous measurements with blade-mounted strain gauges were performed under engine representative conditions. To the best knowledge of the authors, this is the first publication which presents comprehensive experimental unsteady pressure measurements during forced response for highspeed radial compressors. Experimental data were obtained for both resonance and off-resonance conditions with uniquely tailored inlet distortion. This paper covers aspects relating to the design of fast response pressure sensors and their installation on thin impeller blades. Additionally, sensor properties are outlined with a focus on calibration and measurement uncertainty estimations. The second part of this paper presents unsteady pressure results taken for a number of inlet distortion cases. It will be shown that the intended excitation order due to inlet flow distortion is of comparable magnitude to the second and third harmonics which are consistently observed in all measurements. Finally, an experimental method will be outlined that enables the measurement aerodynamic work on the blade surface during resonant crossing. This approach quantifies the energy exchange between the blade and the flow in terms of cyclic work along the blade surface. The phase angle between the unsteady pressure and the blade movement will be shown to determine the direction of energy transfer between the blade and the fluid.

scholarly journals Investigation of Flows in Rectangular Diffusers With Inlet Flow Distortion

1982 ◽  
Author(s):  
M. M. Al-Mudhafar ◽  
M. Ilyas ◽  
F. S. Bhinder
Keyword(s):  
Experimental Study ◽  
Velocity Profiles ◽  
Pressure Recovery ◽  
Two Dimensional ◽  
Flow Distortion ◽  
Inlet Flow ◽  
Inlet Velocity ◽  
Inlet Distortion ◽  
Mach Numbers ◽  
Inlet Flow Distortion

The results of an experimental study on the influence of severely distorted velocity profiles on the performance of a straight two-dimensional diffuser are reported. The data cover entry Mach numbers ranging from 0.1 to 0.6 and several inlet distortion levels. The pressure recovery progressively deteriorates as the inlet velocity is distorted.

Numerical Investigation of the Effect of Diffuser and Volute Design Parameters on the Performance of a Centrifugal Compressor Stage

2016 ◽  
Author(s):  
Lei Yu ◽  
William T. Cousins ◽  
Feng Shen ◽  
Georgi Kalitzin ◽  
Vishnu Sishtla ◽  
...  
Keyword(s):  
Centrifugal Compressor ◽  
Gas Flow ◽  
Pressure Rise ◽  
Design Parameters ◽  
Compressor Stage ◽  
Flow Distortion ◽  
Cross Sectional ◽  
Centrifugal Stage ◽  
And Performance ◽  
The Impact

In this effort, 3D CFD simulations are carried out for real gas flow in a refrigeration centrifugal compressor. Both commercial and the in-house CFD codes are used for steady and unsteady simulations, respectively. The impact on the compressor performance with various volute designs and diffuser modifications are investigated with steady simulations and the analysis is focused on both the diffuser and the volute loss, in addition to the flow distortion at impeller exit. The influence of the tongue, scroll diffusion ratio, diffuser length, and cross sectional area distribution is examined to determine the impact on size and performance. The comparisons of total pressure loss, static pressure recovery, through flow velocity, and the secondary flow patterns for different volute designs show that the performance of the centrifugal compressor depends upon how well the scroll portion of the volute collects the flow from the impeller and achieves the required pressure rise with minimum flow losses in the overall diffusion process. Finally, the best design is selected based on compressor stage pressure rise and peak efficiency improvement. An unsteady simulation of the full wheel compressor stage was carried out to further examine the interaction of impeller, diffuser and the volute. The unsteady flow interactions are shown to have a major impact on the performance of the centrifugal stage.

Fan Aerodynamics With a Short Intake at High Angle of Attack

2020 ◽  
Author(s):  
Ben Mohankumar ◽  
Cesare A. Hall ◽  
Mark J. Wilson
Keyword(s):  
Pressure Ratio ◽  
Angle Of Attack ◽  
Radial Pressure ◽  
Separation Mechanism ◽  
Flow Distortion ◽  
Ratio Distribution ◽  
Rotor Design ◽  
Velocity Triangle ◽  
Tip Velocity ◽  
High Work

Abstract Future turbofan engines seek shorter intakes to reduce the cruise fuel burn of a low pressure ratio, large diameter fan. However, shorter intakes increase the level of flow distortion entering the rotor when the aircraft angle of attack (AOA) is high, reducing thrust when critically needed. This paper considers how the fan rotor radial pressure ratio distribution and tip velocity triangle can be designed to improve thrust at high AOA. Full annulus, unsteady CFD is performed on three rotor designs coupled to a short intake. We show that rotor design for high AOA should be guided by three flow mechanisms. Mechanism i) is caused by high Mach number flow over the bottom intake lip, which chokes the rotor leading to high loss. Mechanism ii) is the loss generation in the rotor tip as it passes through an intake separation. Mechanism iii) shows radial flows through the rotor change both the amount and the way work is imparted on the flow. Two comparable rotor design philosophies for high thrust are proposed; high work or low loss. Rotors designed to a mid-high radial pressure ratio distribution impart high work on streamlines that migrate radially towards the hub and exit the rotor at highly cambered sections. Meanwhile, tip-high designs reduce choking losses in the midspan when operating with a separated intake, particularly when the tip velocity triangle is designed to high axial velocity diffusion over high camber. However, such designs suffer with higher tip losses after exiting an intake separation.

A Scalability Study of the Multirotor Biplane Tailsitter Using Conceptual Sizing

2020 ◽  
Vol 65 (1) ◽  
pp. 1-18
Author(s):  
Ananth Sridharan ◽  
Bharath Govindarajan ◽  
Inderjit Chopra
Keyword(s):  
Power Plants ◽  
Transmission Efficiency ◽  
Rotor Blades ◽  
Transmission Model ◽  
Design Parameters ◽  
Skin Thickness ◽  
Weight Class ◽  
Rotor Design ◽  
Load Carrying ◽  
Beam Lattice

This paper presents a methodology for preliminary sizing of unconventional rotorcraft using a physics-based approach to estimate the weight of primary load-carrying members and rotor efficiencies. The methodology is demonstrated for a quadrotor biplane tailsitter, a tilt-body configuration that can operate in both helicopter and airplane mode. A beam lattice framework for the airframe structure is iteratively adjusted in the sizing loop to accommodate the limit loads. A similar semianalytical approach is followed to size and estimate weight of the rotor blades. Using this analysis, a consistent combination of vehicle macrodimensions (rotor radius, wing span) and tip speed as well as detailed design parameters (spar height, skin thickness, and cross-section weight) are obtained simultaneously. To compare the effectiveness of various power plants within a weight class, the sizing methodology was modified to identify the payload for three different vehicle takeoff weights: 20, 50, and 1000 lb. To enable operation within constrained urban canyons, the effect of restricting maximum vehicle dimensions to 10 ftfor the 1000-lb designs is also examined. An electric transmission model is used in these designs owing to its relative insensitivity of transmission efficiency to the operating RPM. A variable-pitch and variable-RPM rotor design allows for control redundancy within each rotor.

Forward Swept Rotor Studies in Multistage Fans With Inlet Distortion

2002 ◽  
Author(s):  
A. R. Wadia ◽  
P. N. Szucs ◽  
D. W. Crall ◽  
D. C. Rabe
Keyword(s):  
Pressure Ratio ◽  
Flow Distortion ◽  
Two Stage ◽  
Good Efficiency ◽  
Guide Vanes ◽  
Stall Margin ◽  
High Pressure Ratio ◽  
Inlet Distortion ◽  
Inlet Guide Vanes ◽  
Current Production

Previous experimental and analytical studies conducted to compare the performance of transonic swept rotors in single stage fans have demonstrated the potential of significant improvements in both efficiency and stall margin with forward swept blading. This paper extends the assessment of the payoff derived from forward sweep with respect to aerodynamic performance and stability to multistage configurations. The experimental investigation compares, on a back-to-back test basis, two builds of an advanced good efficiency, high pressure ratio, two-stage fan configuration tested alternately with a radial and a forward swept stage 1 blade. In the two-stage evaluations, the testing was extended to include the effect on inlet flow distortion. While the common second stage among the two builds prevented the overall fan from showing clean inlet performance and stability benefits with the forward swept rotor 1, this configuration did demonstrate superior front stage efficiency and tolerance to inlet distortion. Having obtained an already low distortion sensitivity with the radial rotor 1 configuration relative to current production military fan standards, the sensitivity to inlet distortion was halved with the forward swept rotor 1 configuration. In the case of the 180-degree one-per-rev distortion pattern, the two-stage configuration was evaluated both with and without inlet guide vanes (IGVs). The presence of the inlet guide vanes had a profound impact in lowering the two stage fan’s sensitivity with inlet distortion.

Effects of Flow Distortions as They Occur in S-Duct Inlets on the Performance and Stability of a Jet Engine

2015 ◽  
Author(s):  
Rudolf. P. M. Rademakers ◽  
Stefan Bindl ◽  
Reinhard Niehuis
Keyword(s):  
Mesh Size ◽  
Experimental Investigations ◽  
Test Bed ◽  
Flow Distortion ◽  
Jet Engine ◽  
Jet Propulsion ◽  
Inlet Distortion ◽  
Flow Phenomena ◽  
The Impact ◽  
Duct Design

One of the research areas at the Institute of Jet Propulsion focuses on the design and optimization of s-shaped engine inlet configurations. The distortion being evoked within such inlet ducts should be limited to ensure an optimal performance, stability, and durability of the engine’s compression system. Computational Fluid Dynamics (CFD) play a major role in the design process of bent engine inlet ducts. The flow within such ducts can be computed, distortion patterns can be visualized, and related distortion coefficients are easily calculated. The impact of a distortion on flow phenomena within the compressor system can, however, only be computed with major computational efforts and thus the quality of an s-duct design in development is usually assessed by analyzing the evoked distortion with suitable distortion coefficients without a true knowledge of the duct’s influence on the downstream propulsion system. The influence of inlet distortion on both the performance and stability of the Larzac 04 jet engine was parameterized during experimental investigations at the engine test bed of the Institute of Jet Propulsion. Both pressure and swirl distortion patterns as they typically occur in s-duct inlet configurations were reproduced with distortion generators. Pressure distortion patterns were generated using seven types of distortion screens. The intensity of the distortion varies with the mesh size of the screen whereas the extension of the distortion is defined by the dimensions of the screen in radial and circumferential direction. A typical counter rotating twin-swirl was generated with a deltawing installed upstream of the compressor system. First, the development of flow distortion was analyzed for several engine operating points (EOPs). A linear relation between the total pressure loss in the engine inlet and the EOPs was found. Secondly, the flow within the compressor system with an inlet distortion was analyzed and unsteady flow phenomena were detected for severe inlet distortions. Finally, the effect of both pressure and swirl distortion on the performance and stability of the test vehicle was parameterized. A loss in engine performance with increasing inlet distortion is observable. The limiting inlet distortion with respect to engine stability was found and moreover it was shown that pressure distortion has a stronger influence on the stability of the compressor system compared to a counter rotating twin-swirl distortion. The presented parameterization is essential for the s-duct design, which is under development for an experimental set-up with the Larzac 04 jet engine.

Unsteady Computational Fluid Dynamics Investigation on Inlet Distortion in a Centrifugal Compressor

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Armin Zemp ◽  
Albert Kammerer ◽  
Reza S. Abhari
Keyword(s):  
Centrifugal Compressor ◽  
Temporal Evolution ◽  
Flow Distribution ◽  
Forced Response ◽  
Inlet Section ◽  
Flow Distortion ◽  
Inlet Flow ◽  
Inlet Distortion ◽  
Forcing Function ◽  
Unsteady Fluid

Blade failure in turbomachinery is frequently caused by an excessive resonant response. Forced response of the blades originates from unsteady fluid structure interactions as conditioned in the inlet section by duct bends, struts, or inlet guide vanes. This paper presents the computational part of a research effort that focuses on the blade forced response in a centrifugal compressor. Unsteady fluid flow simulations are used to quantify the forcing function acting on the compressor blades due to inlet flow distortion. The measured inlet flow distribution is applied as inlet boundary conditions in the computation. The unsteady investigation provided the temporal evolution of the distorted flow through the compressor. The time-resolved blade pressure distribution showed the temporal evolution of the dynamic load on the blade surface caused by the inlet distortion. The results suggest that the forcing function is most sensitive in the leading edge region due to inlet angle variations. Toward the impeller stability line the increase in incidence caused separation on the suction side of the main blade and therefore considerably altered the amplitude and the phase angle of the unsteadiness. The investigation of the effect of idealizing the inlet flow distribution on the forcing function showed an increase in the peak amplitude of approximately 30% compared with the actual inlet flow distribution.

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