The Effect of Blade Count on Body Force Model Performance for Axial Fans

2021 ◽  
pp. 1-37
Author(s):  
Palak Saini ◽  
Jeff Defoe
Keyword(s):  
Body Force ◽  
Computational Cost ◽  
Model Performance ◽  
Aircraft Engine ◽  
The Body ◽  
Force Model ◽  
Cooling Flows ◽  
Cooling Fans ◽  
Axial Fans ◽  
Spanwise Flow

Abstract Body force models enable inexpensive numerical simulations of turbomachinery. The approach replaces the blades with sources of momentum/energy. Such models capture a “smeared out” version of the blades' effect on the flow, reducing computational cost. The body force model used in this paper has been widely used in aircraft engine applications. Its implementation for low speed, low solidity (few blades) turbomachines, such as automotive cooling fans, enables predictions of cooling flows and component temperatures without calibrated fan curves. Automotive cooling fans tend to have less than 10 blades, which is approximately 50% of blade counts for modern jet engine fans. The effect this has on the body force model predictions is unknown and the objective of this paper is to quantify how varying blade count affects the accuracy of the predictions for both uniform and non-uniform inflow. The key findings are that reductions in blade metal blockage combined with spanwise flow redistribution drives the body force model to more accurately predict work coefficient as the blade count decreases, and that reducing the number of blades is found to have negligible impacts on upstream influence and distortion transfer in non-uniform inflow until extremely low blade counts (such as 2) are applied.

The Effect of Blade Count on Body Force Model Performance for Axial Fans

2020 ◽  
Author(s):  
Palak Saini ◽  
Jeff Defoe
Keyword(s):  
Body Force ◽  
Computational Cost ◽  
Model Performance ◽  
Aircraft Engine ◽  
The Body ◽  
Force Model ◽  
Cooling Flows ◽  
Cooling Fans ◽  
Axial Fans ◽  
Spanwise Flow

Abstract Body force models enable inexpensive numerical simulations of turbomachinery. The approach replaces the blades with sources of momentum/energy. Such models capture a “smeared out” version of the blades’ effect on the flow, reducing computational cost. The body force model used in this paper has been widely used in aircraft engine applications. Its implementation for low speed, low solidity (few blades) turbomachines, such as automotive cooling fans, enables predictions of cooling flows and component temperatures without calibrated fan curves. Automotive cooling fans tend to have less than 10 blades, which is approximately 50% of blade counts for modern jet engine fans. The effect this has on the body force model predictions is unknown and the objective of this paper is to quantify how varying blade count affects the accuracy of the predictions for both uniform and non-uniform inflow. The key findings are that reductions in blade metal blockage combined with spanwise flow redistribution drives the body force model to more accurately predict work coefficient as the blade count decreases, and that reducing the number of blades is found to have negligible impacts on upstream influence and distortion transfer in non-uniform inflow until extremely low blade counts (such as 2) are applied.

scholarly journals Prediction of Crosswind Separation Velocity for Fan and Nacelle Systems Using Body Force Models: Part 1: Fan Body Force Model Generation without Detailed Stage Geometry

2019 ◽  
Vol 4 (4) ◽  
pp. 43 ◽  
Author(s):  
Quentin J. Minaker ◽  
Jeffrey J. Defoe
Keyword(s):  
Design Process ◽  
Body Force ◽  
Pressure Ratio ◽  
Computational Cost ◽  
The Body ◽  
Force Model ◽  
Limited Access ◽  
Turbofan Engines ◽  
Simplifying Assumptions ◽  
Dynamics Simulations

Modern aircraft engines must accommodate inflow distortions entering the engines as a consequence of modifying the size, shape, and placement of the engines and/or nacelle to increase propulsive efficiency and reduce aircraft weight and drag. It is important to be able to predict the interactions between the external flow and the fan early in the design process. This is challenging due to computational cost and limited access to detailed fan/engine geometry. In this, the first part of a two part paper, we present a design process that produces a fan gas path and body force model with performance representative of modern high bypass ratio turbofan engines. The target users are those with limited experience in turbomachinery design or limited access to fan geometry. We employ quasi-1D analysis and a series of simplifying assumptions to produce a gas path and the body force model inputs. Using a body force model of the fan enables steady computational fluid dynamics simulations to capture fan–distortion interaction. The approach is verified for the NASA Stage 67 transonic fan. An example of the design process is also included; the model generated is shown to meet the desired fan stagnation pressure ratio and thrust to within 1%.

scholarly journals Innovations in Body Force Modeling of Transonic Compressor Blade Rows

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
David J. Hill ◽  
Jeffrey J. Defoe
Keyword(s):  
Total Pressure ◽  
Body Force ◽  
Computational Cost ◽  
Pressure Rise ◽  
The Body ◽  
Force Model ◽  
Axial Fan ◽  
Compressor Blades ◽  
Time Resolved ◽  
Transonic Compressor

Aeroengine fans and compressors increasingly operate subject to inlet distortion in the transonic flow regime. In this paper, innovations to low-order numerical modeling of fans and compressors via volumetric source terms (body forces) are presented. The approach builds upon past work to accommodate any axial fan/compressor geometry and ensures accurate work input and efficiency prediction across a range of flow coefficients. In particular, the efficiency drop-off near choke is captured. The model for a particular blade row is calibrated using data from single-passage bladed computations. Compared to full-wheel unsteady computations which include the fan/compressor blades, the source term model approach can reduce computational cost by at least two orders of magnitude through a combination of reducing grid resolution and, critically, eliminating the need for a time-resolved approach. The approach is applied to NASA stage 67. For uniform flow, at 90% corrected speed and peak-efficiency, the body force model is able to predict the total-to-total pressure rise coefficient of the stage to within 1.43% and the isentropic efficiency to within 0.03%. With a 120∘ sector of reduced inlet total pressure, distortion transfer through the machine is well-captured and the associated efficiency penalty predicted with less than 2.7% error.

scholarly journals Computational Modeling of Vortex Generators for Turbomachinery

2002 ◽  
Author(s):  
R. V. Chima
Keyword(s):  
Computational Models ◽  
Body Force ◽  
Secondary Flows ◽  
The Body ◽  
Vortex Generators ◽  
Force Model ◽  
Suction Surface ◽  
Near Surface ◽  
Compressor Rotor ◽  
Surface Particle

In this work computational models were developed and used to investigate applications of vortex generators (VGs) to turbomachinery. The work was aimed at increasing the efficiency of compressor components designed for the NASA Ultra Efficient Engine Technology (UEET) program. Initial calculations were used to investigate the physical behavior of VGs. A parametric study of the effects of VG height was done using 3-D calculations of isolated VGs. A body force model was developed to simulate the effects of VGs without requiring complicated grids. The model was calibrated using 2-D calculations of the VG vanes and was validated using the 3-D results. Then three applications of VGs to a compressor rotor and stator were investigated: 1. The results of the 3-D calculations were used to simulate the use of small casing VGs used to generate rotor preswirl or counterswirl. Computed performance maps were used to evaluate the effects of VGs. 2. The body force model was used to simulate large partspan splitters on the casing ahead of the stator. Computed loss buckets showed the effects of the VGs. 3. The body force model was also used to investigate the use of tiny VGs on the stator suction surface for controlling secondary flows. Near-surface particle traces and exit loss profiles were used to evaluate the effects of the VGs.

Rack Level Modeling of Air Flow Through Perforated Tile in a Data Center

2012 ◽  
Author(s):  
Vaibhav K. Arghode ◽  
Pramod Kumar ◽  
Yogendra Joshi ◽  
Thomas S. Weiss ◽  
Gary Meyer
Keyword(s):  
Data Center ◽  
Body Force ◽  
Air Flow ◽  
The Body ◽  
Physical Models ◽  
Cfd Modeling ◽  
Computational Time ◽  
Force Model ◽  
Flow Through ◽  
Tile Surface

Effective air flow distribution through perforated tiles is required to efficiently cool servers in a raised floor data center. We present detailed computational fluid dynamics (CFD) modeling of air flow through a perforated tile and its entrance to the adjacent server rack. The realistic geometrical details of the perforated tile, as well as of the rack are included in the model. Generally models for air flow through perforated tiles specify a step pressure loss across the tile surface, or porous jump model based on the tile porosity. An improvement to this includes a momentum source specification above the tile to simulate the acceleration of the air flow through the pores, or body force model. In both of these models geometrical details of tile such as pore locations and shapes are not included. More details increase the grid size as well as the computational time. However, the grid refinement can be controlled to achieve balance between the accuracy and computational time. We compared the results from CFD using geometrical resolution with the porous jump and body force model solution as well as with the measured flow field using Particle Image Velocimetry (PIV) experiments. We observe that including tile geometrical details gives better results as compared to elimination of tile geometrical details and specifying physical models across and above the tile surface. A modification to the body force model is also suggested and improved results were achieved.

scholarly journals Body-force modeling for aerodynamic analysis of air intake – fan interactions

2016 ◽  
Vol 26 (7) ◽  
pp. 2048-2065 ◽  
Author(s):  
William Thollet ◽  
Guillaume Dufour ◽  
Xavier Carbonneau ◽  
Florian Blanc
Keyword(s):  
Body Force ◽  
Stokes Equations ◽  
The Body ◽  
Test Case ◽  
Force Model ◽  
Strong Impact ◽  
Analytic Model ◽  
Source Terms ◽  
Content Type ◽  
Air Intake

Purpose The purpose of this paper is to explore a methodology that allows to represent turbomachinery rotating parts by replacing the blades with a body force field. The objective is to capture interactions between a fan and an air intake at reduced cost, as compared to full annulus unsteady computations. Design/methodology/approach The blade effects on the flow are taken into account by adding source terms to the Navier-Stokes equations. These source terms give the proper amount of flow turning, entropy, and blockage to the flow. Two different approaches are compared: the source terms can be computed using an analytic model, or they can directly be extracted from RANS computations with the blade’s geometry. Findings The methodology is first applied to an isolated rotor test case, which allows to show that blockage effects have a strong impact on the performance of the rotor. It is also found that the analytic body force model underestimates the mass flow in the blade row for choked conditions. Finally, the body force approach is used to capture the coupling between a fan and an air intake at high angle of attacks. A comparison with full annulus unsteady computations shows that the model adequately captures the potential effects of the fan on the air intake. Originality/value To the authors’ knowledge, it is the first time that the analytic model used in this paper is combined with the blockage source terms. Furthermore, the capability of the model to deal with flows in choked conditions was never assessed.

A No-Calibration Approach to Modelling Compressor Blade Rows With Body Forces Employing Artificial Neural Networks

2019 ◽  
Author(s):  
S. Pazireh ◽  
J. J. Defoe
Keyword(s):  
Neural Network ◽  
Body Force ◽  
Incompressible Flows ◽  
The Body ◽  
Analytical Models ◽  
Force Model ◽  
Body Forces ◽  
Viscous Loss ◽  
Artificial Neural ◽  
Modelling Approach

Abstract Body force modelling in numerical simulations of axial compressors and fans has been used extensively in the literature to assess aerodynamic performance in uniform and non-uniform flow at relatively low computational cost. Existing approaches require calibration or, in the case of purely analytical models, are unable to accurately predict losses. It can also be challenging to capture the chordwise loading distribution with existing analytical models. This paper introduces a new body force modelling approach in which blade loading is computed using an isolated-airfoil, analytical model supplemented by a trained artificial-neural-network-based correction factor for finite pitch effects. The loading model is derived from potential flow theory and accounts for both camber and thickness effects; it captures both the overall and local loading. The approach is currently implemented for low-Mach number (incompressible) flows. The body forces causing flow turning derive directly from the corrected loading model. Forces arising from viscous losses are modeled by solving the integral boundary layer equations along streamlines within blade rows based on the fictitious edge velocities computed by the loading model. The viscous loss force is a function of the local dissipation coefficients. The approach is implemented within a traditional finite-volume computational fluid dynamics solver. In this paper, the application is limited to 2D cascades. To assess the approach, results from the body force model are compared to blade-to-blade solutions from MISES. The key findings are (1) that a relatively modest set of training data for the neural network produces a robust finite pitch correction, and (2) that the modelling approach is able to successfully capture the flow turning and losses associated with a variety of low-speed compressor cascades without any calibration specific to the blade row(s) being modeled.

Numerical Design Study of Duct and Stator for a Pump-Jet Propulsor

2020 ◽  
Author(s):  
Xue-Qin Ji ◽  
Chen-Jun Yang ◽  
Xiao-Qian Dong
Keyword(s):  
Optimal Design ◽  
Body Force ◽  
Swirl Flow ◽  
The Body ◽  
Hydrodynamic Performance ◽  
Navier Stokes ◽  
Strong Interactions ◽  
Force Model ◽  
Computational Domain ◽  
Two Parameters

Abstract The pump-jet propulsor consists of a duct, a rotor and stators which are installed upstream of the rotor to provide pre-swirl flow or downstream of rotor to absorb the kinetic energy in the flow. The strong interactions between the three components and the vehicle are closely related to their design and exert great effect on noise and hydrodynamic performance. This paper attempts to develop an effective and efficient method for the optimal design of the duct and the pre-swirl stators under the influence of vehicle and rotor via viscous flow CFD simulations. In this paper, the two key parameters, attack angle of the duct and pitch angle of pre-swirl stators, are investigated. The numerical simulations are based on the solution of the Reynolds-Averaged Navier-Stokes (RANS) equations using a two-layer realizable k-ε model for turbulence closure. The computational domain is discretized into mixed unstructured cells. The software package STAR-CCM+ is used for both grid generations and flow simulations. The rotor is replaced by the body-force model which is proposed according to the load distribution of the rotor in pump-jet propulsor. Total thrust of body force balances the resistance of a fully-appended underwater vehicle and its propulsor in the self-propulsion simulations and torque is determined by assuming that the propulsive efficiency is 80%. To the end of the optimal design, the total resistance, as the main consideration, and detailed flow field, such as pressure distribution, are numerically investigated for varied attack angles of the duct and pitch angles of pre-swirl stator. It is shown that the two parameters have significant impact on the performance of the propulsor and the recommended design is given.

A Method of Stall and Surge Prediction in Axial Compressors Based On Three-Dimensional Body-Force Model

2021 ◽  
Author(s):  
Hanxuan Zeng ◽  
Xinqian Zheng ◽  
Mehdi Vahdati
Keyword(s):  
Body Force ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Rotating Stall ◽  
The Body ◽  
Force Model ◽  
Computational Domain ◽  
Forward Flow ◽  
Axial Compressors

Abstract The occurrence of stall and surge in axial compressors has a great impact on the performance and reliability of aero-engines. Accurate and efficient prediction of the key features during these events has long been the focus of engine design processes. In this paper, a new body-force model that can capture the three-dimensional and unsteady features of stall and surge in compressors at a fraction of time required for URANS computations is proposed. To predict the rotating stall characteristics, the deviation of local airflow angle from the blade surface is calculated locally during the simulation. According to this local deviation, the computational domain is divided into stalled and forward flow regions, and the body-force field is updated accordingly; to predict the surge characteristics, the local airflow direction is used to divide the computational domain into reverse flow regions and forward flow regions. A single-stage axial compressor and a three-stage axial compressor are used to verify the proposed model. The results show that the method is capable of capturing stall and surge characteristics correctly. Compared to the traditional fully three-dimensional URANS method (fRANS), the simulation time for multi-stage axial compressors is reduced by 1 to 2 orders of magnitude.

Sign in / Sign up

Export Citation Format

Share Document