scholarly journals Two-dimensional simulation of frost formation on the NACA0012 airfoil under strong convection by using the p-VOF method

2021 ◽  
Vol 3 (1) ◽  
Author(s):  
Bin Xia ◽  
Xianghua Xu ◽  
Xingang Liang
Keyword(s):  
Flow Separation ◽  
Volume Fraction ◽  
Early Stage ◽  
Vof Method ◽  
Two Dimensional ◽  
Airfoil Surface ◽  
Frost Formation ◽  
Naca0012 Airfoil ◽  
Strong Convection ◽  
Frost Layer

AbstractA newly developed frosting simulation method, p-VOF method, is applied to simulate the dynamic frost formation on the NACA0012 airfoil under strong convection. The p-VOF method is a pseudo VOF method of the multiphase flow simulation with phase change. By solving a simplified mass conservation equation explicitly instead of the original volume fraction equations in CFD software, the efficiency and robustness of calculation are greatly improved. This progress makes it possible to predict a long-time frost formation. The p-VOF method was successfully applied to the simulation of dynamic frosting on the two-dimensional NACA0012 airfoil under strong convection conditions with constant frost physical properties. The simulation result shows that the average thickness of the frost layer increases, and the frost bulges and flow separation appear earlier, when the airfoil surface temperature decreases or the air humidity increases. The frost bulges and flow separation appear earlier, when the air velocity is faster, the growth rate of the frost layer at the early stage is greater, but the final frost layer is thinner.

Two-Dimensional Simulation of Frost Formation on the NACA0012 Airfoil under Strong Convection by Using the P-VOF Method

2021 ◽  
Author(s):  
Bin Xia ◽  
Xianghua Xu ◽  
Xingang Liang
Keyword(s):  
Flow Separation ◽  
Volume Fraction ◽  
Early Stage ◽  
Simulation Method ◽  
Vof Method ◽  
Two Dimensional ◽  
Frost Formation ◽  
Naca0012 Airfoil ◽  
Strong Convection ◽  
Frost Layer

Abstract A newly developed frosting simulation method, pseudo-VOF (p-VOF) method, has applied to simulate the dynamic frost formation on the NACA0012 airfoil under strong convection. The p-VOF method is a pseudo volume of fraction simulation method of the multiphase flow with phase change. By solving a simplified mass conservation equation explicitly instead of the original volume fraction equations in CFD software, the efficiency and robustness of calculation are greatly improved. This progress makes it possible to predict a long-time frost formation. The p-VOF method was successfully applied to the simulation of dynamic frosting on the two-dimensional NACA0012 airfoil under strong convection conditions with constant frost physical properties. The simulation result shows that the average thickness of the frost layer increases, and the frost bulges and flow separation appear earlier, when the airfoil surface temperature decreases or the air humidity increases. The frost bulges and flow separation appear earlier, when the air velocity is faster, the growth rate of the frost layer at the early stage is greater, but the final frost layer is thinner.

Observations of Early-Stage Frost Formation on a Cold Plate in Atmospheric Air Flow

2003 ◽  
Vol 125 (1) ◽  
pp. 95-102 ◽  
Author(s):  
Chin-Hsiang Cheng ◽  
Keng-Hsien Wu
Keyword(s):  
Growth Rate ◽  
Early Stage ◽  
Air Flow ◽  
Growth Period ◽  
Layer Growth ◽  
Cold Plate ◽  
Frost Formation ◽  
Atmospheric Air ◽  
Frost Layer ◽  
Frost Growth

The present study is conducted to investigate the frost formation on a cold plate in atmospheric air flow by means of experimental and theoretical methods. In order to provide observations for the early stage of the frost growth process, a microscopic image system is used to record the pattern and the thickness of the frost layer per five seconds after the onset of frost formation. In this study, a multiple-step ascending frost growth pattern caused by melting of frost crystals at the frost surface has been observed. Effects of velocity, temperature and relative humidity of air (V,Ta, and ϕ) are studied, and the surface temperature of the cold plate Tw is also varied. The considered ranges of these dominant variables are: 2⩽V⩽13 m/s, 20⩽Ta⩽35°C, 40 percent ⩽ϕ⩽80 percent, and −13⩽Tw⩽−2°C. The theoretical model presented by Cheng and Cheng [22] for predicting the frost growth rate during the frost layer growth period is verified. Results show that the predictions of frost growth rate by the model agree with the experiment data, especially for the frost layer growth period.

Instrumentation For Quantitative Microscopy

1977 ◽  
Vol 35 ◽  
pp. 206-209
Author(s):  
B. Ralph ◽  
A.R. Jones
Keyword(s):  
Volume Fraction ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Automatic Data ◽  
Phase Volume Fraction ◽  
Statistical Confidence ◽  
Resultant Data ◽  
Automatic Data Collection ◽  
Third Dimension ◽  
Evolution Of Microstructure

In all fields of microscopy there is an increasing interest in the quantification of microstructure. This interest may stem from a desire to establish quality control parameters or may have a more fundamental requirement involving the derivation of parameters which partially or completely define the three dimensional nature of the microstructure. This latter categorey of study may arise from an interest in the evolution of microstructure or from a desire to generate detailed property/microstructure relationships. In the more fundamental studies some convolution of two-dimensional data into the third dimension (stereological analysis) will be necessary.In some cases the two-dimensional data may be acquired relatively easily without recourse to automatic data collection and further, it may prove possible to perform the data reduction and analysis relatively easily. In such cases the only recourse to machines may well be in establishing the statistical confidence of the resultant data. Such relatively straightforward studies tend to result from acquiring data on the whole assemblage of features making up the microstructure. In this field data mode, when parameters such as phase volume fraction, mean size etc. are sought, the main case for resorting to automation is in order to perform repetitive analyses since each analysis is relatively easily performed.

Visual and Theoretical Analyses of the Early Stage of Frost Formation on Cold Surfaces

2007 ◽  
Vol 14 (3) ◽  
pp. 257-268 ◽  
Author(s):  
Xiaomin Wu ◽  
WanTian Dai ◽  
XiaoFeng Shan ◽  
Weicheng Wang ◽  
LiMing Tang
Keyword(s):  
Early Stage ◽  
Frost Formation ◽  
Theoretical Analyses

scholarly journals A Sequential Approach for Aerodynamic Shape Optimization with Topology Optimization of Airfoils

2021 ◽  
Vol 26 (2) ◽  
pp. 34
Author(s):  
Isaac Gibert Martínez ◽  
Frederico Afonso ◽  
Simão Rodrigues ◽  
Fernando Lau
Keyword(s):  
Topology Optimization ◽  
Shape Optimization ◽  
Volume Fraction ◽  
Optimization Techniques ◽  
Free Form ◽  
Aerodynamic Shape Optimization ◽  
Sequential Approach ◽  
Airfoil Surface ◽  
Aerodynamic Shape ◽  
Design Variables

The objective of this work is to study the coupling of two efficient optimization techniques, Aerodynamic Shape Optimization (ASO) and Topology Optimization (TO), in 2D airfoils. To achieve such goal two open-source codes, SU2 and Calculix, are employed for ASO and TO, respectively, using the Sequential Least SQuares Programming (SLSQP) and the Bi-directional Evolutionary Structural Optimization (BESO) algorithms; the latter is well-known for allowing the addition of material in the TO which constitutes, as far as our knowledge, a novelty for this kind of application. These codes are linked by means of a script capable of reading the geometry and pressure distribution obtained from the ASO and defining the boundary conditions to be applied in the TO. The Free-Form Deformation technique is chosen for the definition of the design variables to be used in the ASO, while the densities of the inner elements are defined as design variables of the TO. As a test case, a widely used benchmark transonic airfoil, the RAE2822, is chosen here with an internal geometric constraint to simulate the wing-box of a transonic wing. First, the two optimization procedures are tested separately to gain insight and then are run in a sequential way for two test cases with available experimental data: (i) Mach 0.729 at α=2.31°; and (ii) Mach 0.730 at α=2.79°. In the ASO problem, the lift is fixed and the drag is minimized; while in the TO problem, compliance minimization is set as the objective for a prescribed volume fraction. Improvements in both aerodynamic and structural performance are found, as expected: the ASO reduced the total pressure on the airfoil surface in order to minimize drag, which resulted in lower stress values experienced by the structure.

Dynamic Stall Simulation of Flow Over NACA0012 Airfoil at 1 Million Reynolds Number

2015 ◽  
Author(s):  
Venkata Ravishankar Kasibhotla ◽  
Danesh Tafti
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
Dynamic Stall ◽  
Sharp Drop ◽  
Airfoil Surface ◽  
Naca0012 Airfoil ◽  
Reduced Frequency ◽  
Edge Vortex

The paper is concerned with the prediction and analysis of dynamic stall of flow past a pitching NACA0012 airfoil at 1 million Reynolds number based on the chord length of the airfoil and at reduced frequency of 0.25 in a three dimensional flow field. The turbulence in the flow field is resolved using large eddy simulations with the dynamic Smagorinsky model at the sub grid scale. The development of dynamic stall vortex, shedding and reattachment as predicted by the present study are discussed in detail. This study has shown that the downstroke phase of the pitching motion is strongly three dimensional and is highly complex, whereas the flow is practically two dimensional during the upstroke. The lift coefficient agrees well with the measurements during the upstroke. However, there are differences during the downstroke. The computed lift coefficient undergoes a sharp drop during the start of the downstroke as the convected leading edge vortex moves away from the airfoil surface. This is followed by a recovery of the lift coefficient with the formation of a secondary trailing edge vortex. While these dynamics are clearly reflected in the predicted lift coefficient, the experimental evolution of lift during the downstroke maintains a fairly smooth and monotonic decrease in the lift coefficient with no lift recovery. The simulations also show that the reattachment process of the stalled airfoil is completed before the start of the upstroke in the subsequent cycle due to the high reduced frequency of the pitching cycle.

Free vibration analysis of three-layer thin cylindrical shell with variable thickness two-dimensional FGM middle layer under arbitrary boundary conditions

2021 ◽  
pp. 109963622110204
Author(s):  
Xue-Yang Miao ◽  
Chao-Feng Li ◽  
Yu-Lin Jiang ◽  
Zi-Xuan Zhang
Keyword(s):  
Cylindrical Shell ◽  
Boundary Conditions ◽  
Volume Fraction ◽  
Ritz Method ◽  
Admissible Function ◽  
Free Vibration Analysis ◽  
Middle Layer ◽  
Two Dimensional ◽  
Arbitrary Boundary ◽  
Arbitrary Boundary Conditions

In this paper, a unified method is developed to analyze free vibrations of the three-layer functionally graded cylindrical shell with non-uniform thickness. The middle layer is composed of two-dimensional functionally gradient materials (2D-FGMs), whose thickness is set as a function of smooth continuity. Four sets of artificial springs are assigned at the ends of the shells to satisfy the arbitrary boundary conditions. The Sanders’ shell theory is used to obtain the strain and curvature-displacement relations. Furthermore, the Chebyshev polynomials are selected as the admissible function to improve computational efficiency, and the equation of motion is derived by the Rayleigh–Ritz method. The effects of spring stiffness, volume fraction indexes, configuration on of shell, and the change in thickness of the middle layer on the modal characteristics of the new structural shell are also analyzed.

Frost Formation and its Density Behavior on Various Surfaces

2001 ◽  
Author(s):  
Cheolhwan Kim ◽  
Jongmin Shin ◽  
Alexei V. Tikhonov ◽  
Samchul Ha ◽  
Bongjun Choi
Keyword(s):  
Surface Energy ◽  
Dynamic Contact ◽  
Contact Angles ◽  
Test Time ◽  
Test Results ◽  
Plate Temperature ◽  
Specific Test ◽  
Frost Formation ◽  
Frost Layer ◽  
Density Behavior

Abstract An experimental study has been conducted to investigate the effects of surface energy on frost formation. Test samples with three different surfaces of which Dynamic Contact Angles (DCA) are 23, 55 and 88 degrees are installed in a wind tunnel and exposed to a humid airflow. The thickness and the mass of frost layer are measured and used to calculate frost density while frost formation is visualized simultaneously with their measurements. Results show that frost density increases as time increases at specific test conditions. The air Reynolds number, the airflow humidity and the cold plate temperature are maintained at 12,000, 0.0042 kg/kg and −20 degrees Celsius, respectively. The surface with a lower DCA shows a higher frost density for a two-hour test, but no differences in frost density have been found after two hours of frost generation. Empirical correlations for thickness, mass and density are proposed as the functions of test time and surface energy. Visualization of frost generation was in good agreements with test results.

Effect of Fullerene Volume Fraction on Two-Dimensional Crystal-Constructed Supramolecular Liquid Crystals

2018 ◽  
Vol 14 (1) ◽  
pp. 125-129 ◽  
Author(s):  
Peng Shen ◽  
Xiaoyan Zhang ◽  
Huanjun Lu ◽  
Zebin Su ◽  
Yi Zhou ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Volume Fraction ◽  
Two Dimensional ◽  
Dimensional Crystal

Comparison of Two Active Flow Control Mechanisms of Pure Blowing and Pure Suction on a Pitching NACA0012 Airfoil at Reynolds Number of 1 × 106

2018 ◽  
Author(s):  
Ehsan Asgari ◽  
Mehran Tadjfar
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Active Flow Control ◽  
Hysteresis Loops ◽  
Leading Edge ◽  
Control Mechanisms ◽  
Airfoil Surface ◽  
Naca0012 Airfoil ◽  
Maximum Angle ◽  
Active Flow

In this study, we have applied and compared two active flow control (AFC) mechanisms on a pitching NACA0012 airfoil at Reynolds number of 1 × 106 using 2-D computational fluid dynamics (CFD). These mechanisms are continuous blowing and suction which are applied separately on the airfoil which pitches around its quarter-chord in a sinusoidal motion. The location for suction and blowing was determined in our previous study based on the formation of a counter clock-wise vortex near the leading-edge. In our current study, we have compared the effectiveness of pure blowing and pure suction in suppressing the dynamic stall vortex (DSV) which is the main contributor to the drag increase, particularly near the maximum angle of attack (AOA) and in early downstroke motion. The blowing/suction slot is considered as a dent on the airfoil surface which enables the AFC to perform in a tangential manner. This configuration would allow blowing jet to penetrate further downstream and was shown to be more effective compared to a cross-flow orientation. We have compared the two aforementioned mechanisms in terms of hysteresis loops of lift and drag coefficients and have demonstrated the dynamics of flow in controlled and uncontrolled situations.

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