Reducing Nacelle Pressure Drag

2017 ◽  
Author(s):  
D. J. Cerantola ◽  
M. S. Zawislak ◽  
A. M. Birk
Keyword(s):  
Reynolds Number ◽  
Fuel Economy ◽  
Suction Side ◽  
Maximum Diameter ◽  
Radius Of Curvature ◽  
Wall Functions ◽  
Pressure Drag ◽  
Baseline Case ◽  
Operational Range ◽  
Corner Vortex

Decreasing drag on aircraft components was beneficial towards improving fuel economy and operational range. A generic axisymmetric nacelle-strut configuration typical of those housing fuselage-mounted engines was evaluated at a Reynolds number of 6 × 105 based on the nacelle maximum diameter d = 26.5 cm and an angle of attack of 20 deg. It was estimated that drag could be reduced by 20%. Three case studies were evaluated that added a fillet to the nacelle-strut corner, vortex generating triangular tabs, and flow-path obstructing vanes to improve flow control by reducing suction-side separation. Experimental results showed that a 0.11 d radius of curvature fillet reduced drag by 8% with respect to the baseline case. Numerical results employing the realizable k-ε turbulence model with wall functions predicted no improvements with the tabs and an 8% reduction with the vanes.

scholarly journals Simulation of Gas Flow Over a Micro Cylinder

2009 ◽  
Author(s):  
Yuan Hu ◽  
Quanhua Sun ◽  
Jing Fan
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Drag Coefficient ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Low Reynolds Number ◽  
Pressure Drag ◽  
Low Reynolds ◽  
Rarefied Gas Effect ◽  
Gas Effect

Gas flow over a micro cylinder is simulated using both a compressible Navier-Stokes solver and a hybrid continuum/particle approach. The micro cylinder flow has low Reynolds number because of the small length scale and the low speed, which also indicates that the rarefied gas effect exists in the flow. A cylinder having a diameter of 20 microns is simulated under several flow conditions where the Reynolds number ranges from 2 to 50 and the Mach number varies from 0.1 to 0.8. It is found that the low Reynolds number flow can be compressible even when the Mach number is less than 0.3, and the drag coefficient of the cylinder increases when the Reynolds number decreases. The compressible effect will increase the pressure drag coefficient although the friction coefficient remains nearly unchanged. The rarefied gas effect will reduce both the friction and pressure drag coefficients, and the vortex in the flow may be shrunk or even disappear.

Automotive Drag Reduction through Distributed Base Roughness Elements

2014 ◽  
Vol 553 ◽  
pp. 267-272
Author(s):  
Iain Robertson ◽  
Adrien Becot ◽  
Adrian Gaylard ◽  
Ben Thornber
Keyword(s):  
Drag Reduction ◽  
Reference Model ◽  
Detailed Examination ◽  
Rear Face ◽  
Cfd Simulations ◽  
Near Wake ◽  
Wake Structure ◽  
Pressure Drag ◽  
Roughness Elements ◽  
Baseline Case

This paper focuses on the effect of base roughness added to the rear of an automotive reference model, the Windsor model. This roughness addition was found to reduce both the drag and the lift of the model. RANS CFD simulations presented here replicate the experimentally observed drag reduction and enable a detailed examination of the mechanisms behind this effect. Investigations into the wake structure of the configurations with base roughness and the baseline case without base roughness showed the main changes to the wake to include a reduction in the overall size of the wake with base roughness present. Furthermore a reduction in the near wall velocities at the rear of the model caused stretching of the upper and lower vortices, a more turbulent near wake and pressure recovery over much of the rear face. This leads to reduce levels of pressure drag on the model.

The Effect of Pulsed Blowing on the Boundary Layer of a Highly Loaded Low Pressure Turbine Blade

2013 ◽  
Author(s):  
Marion Mack ◽  
Roland Brachmanski ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Trailing Edge ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Highly Loaded

The performance of the low pressure turbine (LPT) can vary appreciably, because this component operates under a wide range of Reynolds numbers. At higher Reynolds numbers, mid and aft loaded profiles have the advantage that transition of suction side boundary layer happens further downstream than at front loaded profiles, resulting in lower profile loss. At lower Reynolds numbers, aft loading of the blade can mean that if a suction side separation exists, it may remain open up to the trailing edge. This is especially the case when blade lift is increased via increased pitch to chord ratio. There is a trend in research towards exploring the effect of coupling boundary layer control with highly loaded turbine blades, in order to maximize performance over the full relevant Reynolds number range. In an earlier work, pulsed blowing with fluidic oscillators was shown to be effective in reducing the extent of the separated flow region and to significantly decrease the profile losses caused by separation over a wide range of Reynolds numbers. These experiments were carried out in the High-Speed Cascade Wind Tunnel of the German Federal Armed Forces University Munich, Germany, which allows to capture the effects of pulsed blowing at engine relevant conditions. The assumed control mechanism was the triggering of boundary layer transition by excitation of the Tollmien-Schlichting waves. The current work aims to gain further insight into the effects of pulsed blowing. It investigates the effect of a highly efficient configuration of pulsed blowing at a frequency of 9.5 kHz on the boundary layer at a Reynolds number of 70000 and exit Mach number of 0.6. The boundary layer profiles were measured at five positions between peak Mach number and the trailing edge with hot wire anemometry and pneumatic probes. Experiments were conducted with and without actuation under steady as well as periodically unsteady inflow conditions. The results show the development of the boundary layer and its interaction with incoming wakes. It is shown that pulsed blowing accelerates transition over the separation bubble and drastically reduces the boundary layer thickness.

Numerical Simulation of Flow around a Cylinder under Different Reynolds Number

2014 ◽  
Vol 543-547 ◽  
pp. 434-440
Author(s):  
Qiang Liu ◽  
Wei Xie ◽  
Wen Yang Duan ◽  
Chang Hong Hu
Keyword(s):  
Reynolds Number ◽  
High Reynolds Number ◽  
Three Dimensional ◽  
Three Dimensional Model ◽  
Initial Field ◽  
Fine Grid ◽  
Flow Around A Cylinder ◽  
Wall Functions ◽  
High Reynolds ◽  
Les Model

Based on fully structured grids parallel numerical simulations of flow around a cylinder under different Reynolds number are carried out. Two-dimensional and three-dimensional models are established at the same time under specific Reynolds number, and further analyze of three-dimensional flow characteristics as well as the generated influence to overall physical quantities are presented. In order to explore efficient high Reynolds number turbulence models, a comparative research of the LES model without wall functions and the Spalart-Allmaras turbulence model is carried out. In order to improve the computational efficiency, a domain decomposition parallel computing strategy is used, and a calculation strategy that results of coarse grid was assigned to fine grid as initial field value by 3D linear interpolation is presented. Simulation results show that: Drag coefficient and Strouhal number have very good consistency with the experimental data, which verifies the correctness of the calculation method; Even if at low Reynolds number (200≤Re≤300), using a three-dimensional model is still necessary; While in the high Reynolds number stage, compared to LES model without wall functions, Spalart-Allmaras model is more applicable and more efficient.

High-Fidelity Simulations of a High-Pressure Turbine Stage: Effects of Reynolds Number and Inlet Turbulence

2021 ◽  
Author(s):  
Yaomin Zhao ◽  
Richard D. Sandberg
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Suction Side ◽  
Rotor Blades ◽  
High Fidelity ◽  
Mean Flow ◽  
High Pressure Turbine ◽  
Flow Shear ◽  
Phase Lock ◽  
The Mean

Abstract We present the first wall-resolved high-fidelity simulations of high-pressure turbine (HPT) stages at engine-relevant conditions. A series of cases have been performed to investigate the effects of varying Reynolds numbers and inlet turbulence on the aerothermal behavior of the stage. While all of the cases have similar mean pressure distribution, the cases with higher Reynolds number show larger amplitude wall shear stress and enhanced heat fluxes around the vane and rotor blades. Moreover, higher-amplitude turbulence fluctuations at the inlet enhance heat transfer on the pressure-side and induce early transition on the suction-side of the vane, although the rotor blade boundary layers are not significantly affected. In addition to the time-averaged results, phase-lock averaged statistics are also collected to characterize the evolution of the stator wakes in the rotor passages. It is shown that the stretching and deformation of the stator wakes is dominated by the mean flow shear, and their interactions with the rotor blades can significantly intensify the heat transfer on the suction side. For the first time, the recently proposed entropy analysis has been applied to phase-lock averaged flow fields, which enables a quantitative characterization of the different mechanisms responsible for the unsteady losses of the stages. The results indicate that the losses related to the evolution of the stator wakes is mainly caused by the turbulence production, i.e. the direct interaction between the wake fluctuations and the mean flow shear through the rotor passages.

Convex Curvature Effects on Film Cooling Adiabatic Effectiveness

2013 ◽  
Author(s):  
James R. Winka ◽  
Joshua B. Anderson ◽  
David G. Bogard ◽  
Michael E. Crawford ◽  
Emily J. Boyd
Keyword(s):  
Film Cooling ◽  
Suction Side ◽  
Surface Curvature ◽  
Radius Of Curvature ◽  
Exact Matching ◽  
Curvature Effects ◽  
Cooling Hole ◽  
Cylindrical Holes ◽  
Series Of Experiments ◽  
Convex Curvature

Surface curvature is known to have significant effects on film cooling performance, with convex curvature inducing increased film effectiveness and concave curvature causing decreased film effectiveness. Generally, these curvature effects have been presumed to scale with 2r/d at the film cooling hole location, where r is the radius of curvature and d is coolant hole diameter. In this study, the validity of this scaling of curvature effects are examined by performing experiments in regions of large and low curvature on a model vane. Single rows of cylindrical holes were placed at various locations along the high curvature section of the suction side of the vane. For the first series of experiments, a single row of holes was placed at two locations with different local surface curvature. The coolant hole diameters were then adjusted to match 2r/d values. Results from these experiments showed that there was better correspondence of film performance when using the 2r/d scaling, but there was not an exact matching of performance. A second series of experiments focused on evaluating the effects of curvature downstream of the coolant holes. One row of holes was placed at a position upstream of the highest curvature, while another row was placed at a downstream position such that the radius of curvature was equivalent for the two rows of holes. Results indicated that the local radius of curvature is not sufficient in understanding the performance of film cooling. Instead, the curvature envelope downstream of the coolant holes plays a significant role on the performance of film cooling for cylindrical holes.

Acoustic and phase portrait analysis of leading-edge roughness element on laminar separation bubbles at low Reynolds number flow

2021 ◽  
pp. 095441002110443
Author(s):  
Hossein Jabbari ◽  
Esmaeili Ali ◽  
Mohammad Hasan Djavareshkian
Keyword(s):  
Reynolds Number ◽  
Phase Portrait ◽  
Separation Bubble ◽  
Roughness Element ◽  
Low Reynolds Number ◽  
Leading Edge ◽  
Suction Side ◽  
Laminar Separation ◽  
Roughness Elements ◽  
Edge Roughness

Since laminar separation bubbles are neutrally shaped on the suction side of full-span wings in low Reynolds number flows, a roughness element can be used to improve the performance of micro aerial vehicles. The purpose of this article was to investigate the leading-edge roughness element’s effect and its location on upstream of the laminar separation bubble from phase portrait point of view. Therefore, passive control might have an acoustic side effect, especially when the bubble might burst and increase noise. Consequently, the effect of the leading-edge roughness element features on the bubble’s behavior is considered on the acoustic pressure field and the vortices behind the NASA-LS0417 cross-section. The consequences express that the distribution of roughness in the appropriate dimensions and location could contribute to increasing the performance of the airfoil and the interaction of vortices produced by roughness elements with shear layers on the suction side has increased the sound frequency in the relevant sound pressure level (SPL). The results have demonstrated that vortex shedding frequency was increased in the presence of roughness compared to the smooth airfoil. Also, more complexity of the phase portrait circuits was found, retrieved from velocity gradient limitation. Likewise, the highest SPL is related to the state where the separation bubble phenomenon is on the surface versus placing roughness elements on the leading edge leads to a negative amount of SPL.

Riblet Application in Compressors: Toward Efficient Blade Design

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
Alexander Hergt ◽  
W. Hage ◽  
S. Grund ◽  
W. Steinert ◽  
M. Terhorst ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Objective Function ◽  
Suction Side ◽  
Skin Friction Coefficient ◽  
Blade Design ◽  
Turbulence Level ◽  
Compressor Cascade ◽  
Flow Solver ◽  
Manufacturing Techniques ◽  
High Level

Nowadays, modern axial compressors have already reached a very high level of development. The current study is focused on the question, if the application of riblets on the surfaces of a highly efficient modern compressor blade can be a further step toward more efficient blade design. Therefore, a highly loaded compressor cascade has been designed and optimized specifically for low Reynolds number (LRN) conditions, as encountered at high altitudes and under consideration of the application of riblets. The optimization was performed at a Mach number of 0.6 and a Reynolds number of 1.5 × 105. Two objective functions were used. The aim of the first objective function was to minimize the cascade losses at the design point and at incidence angles of +5 and −5 deg. The intention of the second objective function was to achieve a smooth distribution of the skin friction coefficient on the suction side of the blade by influencing the blade curvature in order to apply riblets. The MISES flow solver as well as the DLR optimizer “AutoOpti” was used for the optimization process. The developed compressor cascade was investigated in the transonic cascade wind tunnel of DLR in Cologne, where the Reynolds number was varied in the range of 1.5 × 105–9.0 × 105. Furthermore, the measurements were carried out at a low turbulence level of 0.8% and at a high turbulence level of 4%, representative for high pressure compressor stages. The measurement program was divided into two parts. The first part consisted of the investigation of the reference cascade. In the second part of the study, riblets were applied on suction and pressure side of the cascade blades; two different manufacturing techniques, a rolling and a coating techniques, were applied. The rolling technique provides riblets with a width of 70 μm and the coated riblets (CRs) have a width of 50 μm. The wake measurements were performed using a three-hole probe at midspan of the cascade in order to determine the resulting losses of the reference blade and the blades with applied riblets. The detailed analysis of the measurements shows that the riblets have only a slight influence on the viscous losses in the case of the compressor application in this study. Finally, these results are discussed and assessed against the background of feasibility and effort of riblet applications within the industrial design and manufacturing process.

Drawing Engine Universal Performance Characteristics Map Method Based on MATLAB

2012 ◽  
Vol 614-615 ◽  
pp. 361-365 ◽  
Author(s):  
Zhi Peng Zhang ◽  
Jian Zhen Zhang
Keyword(s):  
Fuel Economy ◽  
Performance Characteristics ◽  
Efficient Tool ◽  
Operational Range ◽  
Changing Tendency

The changing tendency of engine performances in its operational range can be directly showed in the engine universal performance characteristics map. Taking advantage of MATLAB mathematic operation, data from engine characteristic tests are processed and the method is simple and credible. The universal performance characteristics map is intuitionist and perspicuous, and is in good fit with data got in tests. It provides a reliable and efficient tool to research into engine performances and automotive drive and fuel economy benefits.

Numerical Investigation on Turbulence Statistics and Heat Transfer of a Circular Jet Impinging on a Roughened Flat Plate

2021 ◽  
Vol 13 (4) ◽  
Author(s):  
Abdulrahman Alenezi ◽  
Abdulrahman Almutairi ◽  
Hamad Alhajeri ◽  
Abdulaziz Gamil ◽  
Faisal Alshammari
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Numerical Study ◽  
Roughness Element ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Target Plate ◽  
Cross Sectional ◽  
Flow Physics ◽  
Baseline Case

Abstract A detailed heat transfer numerical study of a three-dimensional impinging jet on a roughened isothermal surface is presented and is investigated from flow physics vantage point under the influence of different parameters. The effects of the Reynolds number, roughness location, and roughness dimension on the flow physics and heat transfer parameters are studied. Additionally, the relations between average heat transfer coefficient (AHTC) and flow physics including pressure, wall shear and flow vortices with thermodynamic nonequilibrium are offered. This paper studies the effect of varying both location and dimension of the roughness element which took the shape of square cross-sectional continuous ribs to deliver a favorable trade-off between total pressure loss and heat transfer rate. The roughness element was tested for three different radial locations (R/D) = 1, 1.5, and 2 and at each location its height (i.e., width) (e) was changed from 0.25 to 1 mm in incremental steps of 0.25. The study used a jet angle (α) of 90 deg, jet-to-target distance (H/D = 6), and Re ranges from 10,000 to 50,000, where H is the vertical distance between the target plate and jet exit. The results show that the AHTC can be significantly affected by changing the geometry and dimensions of the roughness element. This variation can be either an augmentation of, or decrease in, the (HTC) when compared with the baseline case. An enhancement of 12.9% in the AHTC was achieved by using optimal location and dimensions of the roughness element at specific Reynolds number. However, a diminution between 10% and 30% in (AHTC) was attained by the use of rib height e = 1 mm at Re = 50k. The variation of both rib location and height showed better contribution in increasing heat transfer for low-range Reynolds numbers.

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