A CFD-Based Examination of Rotor-Rotor Separation Effects on Interactional Aerodynamics for eVTOL Aircraft

2021 ◽  
Author(s):  
Richard Healy ◽  
Matthew Misiorowski ◽  
Farhan Gandhi
Keyword(s):  
Fluid Flow ◽  
Flight Speed ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Skew Angle ◽  
Model Simulations ◽  
Eddy Simulation ◽  
Vertical Rotor ◽  
Rotor Disk ◽  
Des Model

This study systematically investigates the aerodynamic interactions of a two-rotor system with a front rotor and an aft rotor aligned with the direction of flow. The rotors are 5.5 ft diameter fixed-pitch rotors operating at approximately 12 lb/ft2 disk loading, representative of large eVTOL aircraft. Fluid flow is simulated using the commercial Navier–Stokes solver, AcuSolve, with a detached eddy simulation (DES) model. Simulations were performed nominally at 40 kt edgewise flight for nine cases corresponding to three values of longitudinal hub–hub separation (2.5R, 3R, 3.5R) and three values of vertical offset (0, 0.25R, 0.5R). Aft rotor performance was compared to an isolated rotor operating in the same conditions in order to quantify the effects of rotor–rotor interaction. For the cases where the aft rotor is closest to the front rotor (2.5R longitudinal offset, zero vertical offset), the aft rotor produced 8.4% less thrust and required 13.4% higher torque than a rotor in isolation. When vertical rotor separation was increased, interactional aerodynamic effects decreased. For a 2.5R longitudinal offset, increasing the vertical offset to 0.5R decreased the lift deficit to 4.6% and the torque penalty to 6.8%. Increasing the longitudinal offset to 3.5R (while keeping the vertical offset at zero) also reduced interactional aerodynamic effects, but reductions in lift deficit and torque penalty were smaller than those observed with 0.5R vertical offset. Reducing disk loading was found to strengthen interactional aerodynamic effects, with an 11.5% thrust deficit at 6 lb/ft2 compared to 9.0% at 12 lb/ft2. An increase in flight speed also increased interactional aerodynamic penalties from 5.4% thrust deficit at 20 kt to 12.2% at 60 kt. The increased interactional aerodynamic penalties with the reduction in disk loading and increase in flight speed were both attributed to an increase in wake skew angle and the resulting decrease in separation between the aft rotor disk and front rotor wake.

Numerical study of unsteady cavitating flows with RANS and DES models

2019 ◽  
Vol 33 (20) ◽  
pp. 1950228
Author(s):  
Chunlai Tian ◽  
Tairan Chen ◽  
Tian Zou
Keyword(s):  
Large Scale ◽  
Numerical Study ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Engineering System ◽  
Detached Eddy Simulation ◽  
Cavitating Flows ◽  
Unsteady Cavitating Flows ◽  
Eddy Simulation ◽  
Des Model

Unsteady cavitating flow with high Reynolds number and significant instability commonly exists in fluid machinery and engineering system. The high-resolution approaches, such as direct numerical simulation and large eddy simulation, are not practical for engineering issues due to the significant cost in the computational resource. The objective of this paper is to provide the approach with Detached-Eddy Simulation (DES) model based on the Reynolds-averaged Navier–Stokes (RANS) equations for predicting unsteady cavitating flows. The credibility of the approach is validated by a set of numerical examples of its application: the unsteady cavitating flows around the two-dimensional (2D) Clark-Y hydrofoil and the three-dimensional (3D) blunt body. It is found that the calculated cavity shapes, cavity lengths and unsteady characteristics by DES model agree well with the experimental measurements and observations. Further analysis indicates that the turbulent eddy viscosity around the cavity and wake region is well predicted by the DES model, which results in the development of large-scale vortexes, and further cavitation instability. The DES model, which exhibits a significantly unsteady 3D behavior, is a more comprehensive turbulence model for unsteady cavitating flows.

scholarly journals ANALYSIS OF SUB-GRID MODELING EFFECTS IN THE SIMULATION OF THE SINGLE-PHASE TURBULENT FLOW IN AN INDUSTRIAL CYCLONE SEPARATOR

2012 ◽  
Vol 11 (1-2) ◽  
pp. 44
Author(s):  
R. V. Salvo ◽  
F. J. Souza ◽  
D. A. M. Martins
Keyword(s):  
Turbulence Modeling ◽  
Swirling Flow ◽  
Experimental Results ◽  
Navier Stokes ◽  
Cyclone Separator ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Volume Cell ◽  
Des Model

In the present work two turbulence modeling approaches, namely Large Eddy Simulation and Detached Eddy Simulation, are employed to predict turbulent, swirling flow within an industrial cyclone separator running at Reynolds number 267,000. The results from three LES models, Smagorinsky, dynamic and Yakhot, and the SST-DES model of Strelets have been compared to experimental results for the average axial and tangential velocities. The Navier-Stokes solver is based on an unstructured, finite volume, cell-centered algorithm such that the details of the geometry can be accurately represented. Based on the comparison with the experimental results, it has been found that the Yakhot model provides the most accurate predictions for the tangential velocities, whereas the dynamic LES and the Smagorinsky models overpredict it and the SST-DES model underpredicts it. However, the conclusions are different regarding the axial velocity. Implications of the turbulence modeling for the particle separation are discussed.

Numerical study of the flow over the modified simple frigate shape

2020 ◽  
pp. 095441002097775
Author(s):  
Tong Li ◽  
Yibin Wang ◽  
Ning Zhao
Keyword(s):  
Bluff Body ◽  
Recirculation Zone ◽  
Numerical Study ◽  
Reference Value ◽  
Flow Fields ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Simulation Results

The simple frigate shape (SFS) as defined by The Technical Co-operative Program (TTCP), is a simplified model of the frigate, which helps to investigate the basic flow fields of a frigate. In this paper, the flow fields of the different modified SFS models, consisting of a bluff body superstructure and the deck, were numerically studied. A parametric study was conducted by varying both the superstructure length L and width B to investigate the recirculation zone behind the hangar. The size and the position of the recirculation zones were compared between different models. The numerical simulation results show that the size and the location of the recirculation zone are significantly affected by the superstructure length and width. The results obtained by Reynolds-averaged Navier-Stokes method were also compared well with both the time averaged Improved Delayed Detached-Eddy Simulation results and the experimental data. In addition, by varying the model size and inflow velocity, various flow fields were numerically studied, which indicated that the changing of Reynolds number has tiny effect on the variation of the dimensionless size of the recirculation zone. The results in this study have certain reference value for the design of the frigate superstructure.

Detached Eddy Simulation of Transonic Rotor Stall Flutter Using a Fully Coupled Fluid-Structure Interaction

2011 ◽  
Author(s):  
Hongsik Im ◽  
Xiangying Chen ◽  
Gecheng Zha
Keyword(s):  
Stokes Equations ◽  
Rotating Stall ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Weno Scheme ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Stall Flutter ◽  
Fully Coupled

Detached eddy simulation of an aeroelastic self-excited instability, flutter in NASA Rotor 67 is conducted using a fully coupled fluid/structre interaction. Time accurate compressible 3D Navier-Stokes equations are solved with a system of 5 decoupled modal equations in a fully coupled manner. The 5th order WENO scheme for the inviscid flux and the 4th order central differencing for the viscous flux are used to accurately capture interactions between the flow and vibrating blades with the DES (detached eddy simulation) of turbulence. A moving mesh concept that can improve mesh quality over the rotor tip clearance was implemented. Flutter simulations were first conducted from choke to stall using 4 blade passages. Stall flutter initiated at rotating stall onset, grows dramatically with resonance. The frequency analysis shows that resonance occurs at the first mode of the rotor blade. Before stall, the predicted responses of rotor blades decayed with time, resulting in no flutter. Full annulus simulation at peak point verifies that one can use the multi-passage approach with periodic boundary for the flutter prediction.

Detached-Eddy Simulations Over a Simplified Landing Gear

2002 ◽  
Vol 124 (2) ◽  
pp. 413-423 ◽  
Author(s):  
L. S. Hedges ◽  
A. K. Travin ◽  
P. R. Spalart
Keyword(s):  
Stokes Equations ◽  
Separated Flow ◽  
Flow Fields ◽  
Equation Model ◽  
Landing Gear ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Navier Stokes Equations ◽  
Instantaneous Flow ◽  
Eddy Simulation

The flow around a generic airliner landing-gear truck is calculated using the methods of Detached-Eddy Simulation, and of Unsteady Reynolds-Averaged Navier-Stokes Equations, with the Spalart-Allmaras one-equation model. The two simulations have identical numerics, using a multi-block structured grid with about 2.5 million points. The Reynolds number is 6×105. Comparison to the experiment of Lazos shows that the simulations predict the pressure on the wheels accurately for such a massively separated flow with strong interference. DES performs somewhat better than URANS. Drag and lift are not predicted as well. The time-averaged and instantaneous flow fields are studied, particularly to determine their suitability for the physics-based prediction of noise. The two time-averaged flow fields are similar, though the DES shows more turbulence intensity overall. The instantaneous flow fields are very dissimilar. DES develops a much wider range of unsteady scales of motion and appears promising for noise prediction, up to some frequency limit.

scholarly journals Numerical Investigation on Fluid Flow in a 90-Degree Curved Pipe with Large Curvature Ratio

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Yan Wang ◽  
Quanlin Dong ◽  
Pengfei Wang
Keyword(s):  
Fluid Flow ◽  
Internal Flow ◽  
Fluid Flows ◽  
Detached Eddy Simulation ◽  
Number Range ◽  
Curvature Ratio ◽  
Large Curvature ◽  
Curved Pipe ◽  
Eddy Simulation ◽  
Curved Pipes

In order to understand the mechanism of fluid flows in curved pipes, a large number of theoretical and experimental researches have been performed. As a critical parameter of curved pipe, the curvature ratioδhas received much attention, but most of the values ofδare very small (δ<0.1) or relatively small (δ≤0.5). As a preliminary study and simulation this research studied the fluid flow in a 90-degree curved pipe of large curvature ratio. The Detached Eddy Simulation (DES) turbulence model was employed to investigate the fluid flows at the Reynolds number range from 5000 to 20000. After validation of the numerical strategy, the pressure and velocity distribution, pressure drop, fluid flow, and secondary flow along the curved pipe were illustrated. The results show that the fluid flow in a curved pipe with large curvature ratio seems to be unlike that in a curved pipe with small curvature ratio. Large curvature ratio makes the internal flow more complicated; thus, the flow patterns, the separation region, and the oscillatory flow are different.

Numerical Investigation of Energy Saving Device Effects on Ships With Propeller-Hull Interactions

2018 ◽  
Author(s):  
Ravi Chaithanya Mysa ◽  
Le Quang Tuyen ◽  
Ma Shengwei ◽  
Vinh-Tan Nguyen
Keyword(s):  
Energy Saving ◽  
Full Scale ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Propulsion Efficiency ◽  
Operational Conditions ◽  
Ship Resistance ◽  
The Past ◽  
Eddy Simulation ◽  
Flow Features

Energy saving devices (ESD) such as propeller ducts, pre-swirl stators, pre-nozzles, etc have been explored as a more economic and reliable approach to reduce energy consumption for both in-operation and newly design ships over the past decades. Those energy saving devices work in the principle of reducing ship resistance and improving propulsion efficiency as well as hull-propeller interactions. Potential saving from various types of ESD have been reported in literature from the range of 3–9% [1] for propulsion efficiency dependent on different measures. Deployment of those devices on actual full-scale ships has been limited over the past years. One of the key obstacles in application of ESD is the lack of confidence in measuring its efficiency on full-scale ships in actual operational conditions. Advances in computational fluid dynamics (CFD) has provided an alternative approach from model scale test to better understand uncertainties in prediction of ESD efficiency in full-scale ship operations [Shin et al, 2013]. In this work a high fidelity CFD model is presented for investigation effects of pre-nozzles on propulsion efficiency and ship resistance. The model is based on the Reynolds Average Navier-Stokes (RANS) solver with different turbulent models including a hybrid detached eddy simulation (DES) approach for predictions of complex near body flow features as well as in the wake regions from hull and propeller. The model is validated with model test for both towing and self-propulsion conditions. Finally a study of pre-nozzle effects on propeller efficiency as well as hull-propeller interaction is presented and compared with available experimental data (Tokyo 2015 Workshop). The current work constitutes a fundamental approach towards designing more efficient ESD for a specific hull form and propeller.

Current Capabilities of DES and LES for Submarines at Straight Course

2010 ◽  
Vol 54 (03) ◽  
pp. 184-196 ◽  
Author(s):  
N. Alin ◽  
R.E. Bensow ◽  
C. Fureby ◽  
T. Huuva ◽  
U. Svennberg
Keyword(s):  
Statistical Moments ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Complex Flow ◽  
First Order ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Actuator Disc ◽  
Rans Models ◽  
Coarse Grids

The flow around an axisymmetric hull, with and without appendages, is investigated using large eddy simulation (LES), detached eddy simulation (DES), and Reynolds averaged Navier Stokes (RANS) models. The main objectives of the study is to investigate the effect of the different simulation methods and to demonstrate the feasibility of using DES and LES on relatively coarse grids for submarine flows, but also to discuss some generic features of submarine hydrodynamics. For this purpose the DARPA Suboff configurations AFF1 (bare hull) and AFF8 (fully appended model) are used. The AFF1 case is interesting because it is highly demanding, in particular for LES and DES, due to the long midship section on which the boundary layer is developed. The AFF8 case represents the complex flow around a fully appended submarine with sail and aft rudders. An actuator disc model is used to emulate some of the effects of the propulsor for one of the AFF8 cases studied. Results for the AFF8 model are thus presented for both "towed" and "self-propelled" conditions, where as for the bare hull, only a "towed" condition is considered. For the AFF1 and the "towed" AFF8 cases experimental data are available for comparison, and the results from both configurations show that all methods give good results for first-order statistical moments although LES gives a better representation of structures and second-order statistical moments in the complex flow in the AFF8 case.

Application of Detached Eddy Simulation to a Subsonic Compressor Rotor

2008 ◽  
Author(s):  
Chunwei Gu ◽  
Fan Feng ◽  
Xuesong Li ◽  
Meilan Chen
Keyword(s):  
Wake Flow ◽  
Leakage Flow ◽  
Separation Region ◽  
Detached Eddy Simulation ◽  
Tip Leakage Flow ◽  
Blade Loading ◽  
Tip Leakage ◽  
Eddy Simulation ◽  
Compressor Rotor ◽  
Des Model

An attempt is made in the present paper to apply DES (Detached Eddy Simulation), which is based on S-A model of RANS, for investigating the flow field around a subsonic compressor rotor with a tip clearance of 2% blade height. Comparison of the results by DES and S-A model shows that DES model can capture more intensive vortex flow, such as tip leakage flow, double leakage flow, as well as interaction between the leakage flow and wake flow downstream of the rotor passage. DES model predicts more complicated flow at the separation region near the hub. DES simulation for different operation conditions also reveals interesting details. The shedding angle and strength of the tip leakage flow changes with the blade loading. The starting point of the leakage vortex moves towards the leading edge when the blade loading increases. Double leakage is observed only at the design and higher loading conditions, and is not at a lower loading condition. The tip leakage vortex splits into two branches downstream of the rotor blade due to interaction with the wake flow. Instantaneous results show unsteadiness of the tip leakage vortex. Alternating regions of higher and lower loss is found along the time-averaged leakage vortex trajectory. Obvious is also the unsteadiness in the separation region near the hub.

A Comparative Study of DES and URANS in a Two-Pass Internal Cooling Duct With Normal Ribs

2005 ◽  
Author(s):  
Aroon K. Viswanathan ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Secondary Flows ◽  
Navier Stokes ◽  
Internal Cooling ◽  
Detached Eddy Simulation ◽  
Mean Flow ◽  
Streamline Curvature ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Developing Flow

The capabilities of the Detached Eddy Simulation (DES) and the Unsteady Reynolds Averaged Navier-Stokes (URANS) versions of the 1988 κ-ω model in predicting the turbulent flow field and the heat transfer in a two-pass internal cooling duct with normal ribs is presented. The flow is dominated by the separation and reattachment of shear layers; unsteady vorticity induced secondary flows and strong streamline curvature. The techniques are evaluated in predicting the developing flow at the entrance to the duct and downstream of the 180° bend, fully-developed regime in the first pass, and in the 180° bend. Results of mean flow quantities, secondary flows, friction and heat transfer are compared to experiments and Large-Eddy Simulations (LES). DES predicts a slower flow development than LES, while URANS predicts it much earlier than LES computations and experiments. However it is observed that as fully developed conditions are established, the capability of the base model in predicting the flow and heat transfer is enhanced by switching to the DES formulation. DES accurately predicts the flow and heat transfer both in the fully-developed region as well as the 180° bend of the duct. URANS fails to predict the secondary flows in the fully-developed region of the duct and is clearly inferior to DES in the 180° bend.

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