- By LiuXing, Senior Flow Measurement Engineer with 15+ years experience in ultrasonic flowmeter R&D,
certified in CFD analysis (ANSYS Fluent Professional)
Engineering Value of Insertion Ultrasonic Flow Meter Pipeline Structure Simulation
Why is Simulation Technology Needed?
In practical engineering, the performance of insertion ultrasonic flow meters is significantly affected by pipeline conditions. Traditional methods rely on repeated on-site debugging, which is not only costly but may also reveal design defects only after commissioning. The introduction of simulation technology has changed this situation, enabling engineers to identify and solve potential problems at the design stage.
Its core value lies in: transferring "trial-and-error costs" from the field to computers, replacing expensive physical experiments with numerical calculations.
Six Major Engineering Problems Solved by Simulation
How to Determine Probe Position
Flow velocity in pipelines is not uniformly distributed. Elbows and valves create local vortices, and installing probes in these areas will lead to distorted readings. Engineers use fluid mechanics calculations to visualize velocity vectors at every point in the pipeline, thereby selecting relatively stable flow field cross-sections for sensor installation, which is essential for accurate flow profile correction factor (FPCF) determination.
Practice shows: minor differences in probe inclination angle (at the 5-degree level) will change the flow state in the measurement area. Systematically testing multiple angle configurations to find the solution with minimum error is almost impractical in physical experiments, but computational analysis can be completed within days while accounting for transducer protrusion and recess effects.
Where is the Accuracy Bottleneck
Ultrasonic measurement relies on the "time difference" principle, and changes in fluid parameters (temperature, pressure, composition) all affect sound velocity. Simple empirical formulas are difficult to cover all operating conditions, especially when meeting custody transfer accuracy requirements.
Simulation establishes the mapping relationship between input parameters and measurement deviation through Reynolds number dependency analysis. For example, when fluid temperature fluctuates ±10℃, how much does sound velocity change? How does this change translate into flow error? With this quantitative data, effective temperature compensation algorithms can be designed.
How to Handle Complex Flow States
The laminar flow model in textbooks rarely appears in actual pipelines. Turbulence, secondary flow, and even gas-liquid two-phase flow cause velocity profiles to severely deviate from ideal states. Computational Fluid Dynamics (CFD) can reproduce these complex phenomena. Engineering cases show: significant velocity skewness still exists 15 pipe diameters downstream of a certain 90-degree bend. Without understanding this, flow calculated according to standard flow field assumptions may deviate by several percentage points, particularly affecting multipath ultrasonic flow meter integration accuracy.
Acoustic Wave Propagation Path Optimization
Ultrasonic waves encounter interference such as pipe wall reflections, weld scattering, and medium non-uniformity during propagation. The cumulative effect of these factors may weaken signal strength or introduce noise.
Acoustic simulation using acoustic ray tracing simulation techniques reveals the actual trajectory of beams inside pipelines. Some geometric configurations produce "acoustic shadow zones," resulting in extremely weak received signals; other configurations, although having strong signals, have multipath effects causing waveform distortion. Through comparative analysis, engineers can select the arrangement scheme with optimal signal-to-noise ratio.
Performance Assurance Under Installation Constraints
Standard specifications typically require 20 pipe diameters of upstream straight pipe section, but field conditions often cannot meet this requirement. Pipeline modification costs may reach hundreds of thousands of dollars.
Simulation provides feasibility assessment for "non-standard installation." By calculating the degree of flow field recovery under different straight pipe section lengths, combined with multi-path configuration compensation technology using Gauss-Jacobi integration method, qualified accuracy may be achieved in spaces with only 6-8 pipe diameters. This requires customized analysis for specific projects, rather than simply applying specifications, while ensuring ISO 17089 compliance validation.
Applicability to Special Media
Operating conditions such as high-viscosity liquids, slurries containing solid particles, and high-temperature high-pressure gases have flow characteristics that differ significantly from conventional fluids. Rash installation may lead to equipment damage or measurement failure.
Simulation allows testing extreme conditions in virtual environments. For example, calculating whether the impact force of high-velocity gas flow on the probe will cause structural resonance through vortex shedding frequency prediction; or analyzing whether particle impact frequency will accelerate sensor wear. This information guides material selection and structural reinforcement design.
Boundaries of Technical Application
Simulation is not omnipotent. Its accuracy depends on:
- Whether the mathematical model covers real physical processes
- Whether boundary condition settings conform to actual situations
- Whether computational resources are sufficient for refined solution
For completely new flow phenomena or extreme operating conditions, simulation results need experimental data validation. Nevertheless, simulation can still greatly narrow the experimental scope, focus on key parameters, and significantly improve research and development efficiency.
Figure 3.1: Insertion-type Ultrasonic Flowmeter
Figure 3.1 shows a commonly used insertion-type ultrasonic flowmeter. Its working principle is to install a pair of ultrasonic sensors on both sides of the pipeline, and achieve accurate flow measurement by detecting and calculating the difference between the ultrasonic pulse velocities in downstream and upstream flow. During the measurement process, the sensors alternately transmit and receive ultrasonic signals in opposite directions. The ultrasonic signals propagate faster in downstream flow than in upstream flow; when the fluid is stationary, the time difference is zero. Therefore, by measuring the propagation time of ultrasonic waves in downstream and upstream flow, the time difference t can be obtained. According to the relationship between t and flow velocity V, the average flow velocity of the fluid can be indirectly measured, and the volumetric flow rate Q can be calculated based on the pipeline cross-sectional area.
The fluid channel design should consider the fluid flow velocity and flow range, where the pipeline design needs to focus more on the fluid flow velocity range to ensure the accuracy of flow measurement. Excessively high or low fluid flow velocity will ultimately affect the propagation characteristics of ultrasonic signals.
The pipeline dimensions, namely the inner diameter of the pipeline, need to match the inner diameter of the measured pipeline to reduce disturbance to fluid flow and thus avoid affecting the final measurement results. The support structure in the pipeline structure should select corrosion-resistant and wear-resistant materials to extend service life; at the same time, reasonable design is needed to ensure its stability under high flow velocity or high pressure. The ultrasonic transducer needs to select an appropriate ultrasonic transducer type (such as guided wave type or reflection type) according to application requirements, and then select an appropriate position to install the ultrasonic transducer to ensure that the ultrasonic signal can effectively pass through the entire pipeline.
In addition to the above factors, research conducted by Tang Xiaoyu[103] and other scholars from Zhejiang University also includes: under 90° bend and 180° bend conditions, the influence of non-ideal flow velocity distribution on each acoustic path of the ultrasonic flowmeter, especially the impact on flow velocity measurement and flowmeter accuracy. Zhang Zhijun and Zhu Yingsheng[102] and other scholars, based on previous research, used CFD simulation technology to conduct simulation analysis on 7 angles (at 5° intervals) between 30° and 60° for ultrasonic transducer installation angles. The results show that: different installation angles affect the flow velocity distribution in the groove portion of the acoustic path. At the same time, the relative error between the simulated flow velocity and the ideal flow velocity was analyzed, and it was determined that the optimal transducer installation angle for the designed DN80 diameter gas ultrasonic flowmeter is 50°.
Insertion-type Ultrasonic Flow Measurement Pipeline Simulation Research
Simulation research considers three aspects:
Fluid dynamics simulation, ultrasonic propagation simulation, and structural mechanics simulation. Using CFD (Computational Fluid Dynamics) models, the fluid flow inside the pipeline can be simulated, and then the effects of factors such as flow velocity distribution and vortex flow on ultrasonic signal propagation can be analyzed. During the simulation process, possible vortices, bubbles, etc. in the fluid should be checked to avoid interference with ultrasonic measurement as much as possible.
Taking the influence of different transducer installation angles on flow velocity distribution as an example, if the total body length of the pipeline flowmeter is L=230 mm and the diameter is D=80 mm. Set the transducer installation angle to 30°~60°, and establish a simulation model at 5° intervals. Different installation angles are shown in Figure 3.2. To reduce computer memory consumption and computational load when ANSYS software performs simulation, the CFD model of the gas ultrasonic flowmeter can be simplified to some extent, only considering the establishment of the inner diameter of the flowmeter housing and the transducer model, with the rest temporarily ignored.
The geometric model is divided into three parts: front pipeline, gas ultrasonic flowmeter, and rear pipeline. Among them, the front and rear pipelines adopt structured mesh, the middle gas ultrasonic flowmeter adopts tetrahedral mesh, and Interface surface connection is used at the connection points, with mesh refinement at the connection surfaces. The outlet and inlet straight pipelines adopt structured mesh as hexahedral mesh, with a maximum mesh size set to 2, Spacing1 (first boundary layer mesh spacing) of 1.5, Ratio1 (first boundary layer mesh growth rate) of 2, Spacing2 (second boundary layer mesh spacing) of 1.5, and Ratio2 (second boundary layer mesh growth rate) of 2. The maximum mesh size of the gas ultrasonic flowmeter body section is 5; local refinement is applied to the transducer mesh with a maximum mesh size of 1.5; local refinement is applied to the interface mesh, keeping the mesh size at 2.
Figure 3.2 Schematic Diagram of Transducers at Different Installation Angles
Transducer Angle Optimization Results chart
| Angle | Vortex Intensity | Pressure Drop | Accuracy | Best Application |
|---|---|---|---|---|
| 30° | High (15% error) | 12% of ΔP | ±1.5% | Not recommended |
| 40° | Medium | 8% of ΔP | ±1.0% | Low Re number |
| 50° | Low | 5% of ΔP | ±0.5% | Optimal (DN80) |
| 60° | Medium | 7% of ΔP | ±0.8% | High velocity |
CFD Simulation Software Selection and Setup
ANSYS Fluent vs COMSOL: Which is better for ultrasonic flowmeter simulation?
Turbulence model comparison: k-ε vs k-ω SST vs RSM for Reynolds number 10⁴-10⁷
Mesh quality criteria: y+ < 1, aspect ratio < 100, skewness < 0.85
Figure 3.3: Modeling Model
Due to the large velocity gradient near the wall surface, boundary layer mesh refinement is adopted, using exponential growth law, with Initial Height (initial height) set to 0.1, Height Ratio (ratio of each boundary layer) of 1.2, Number of Layers (number of boundary layers) of 3, and Total Height (total height of boundary layers) of 0.7. The final total mesh count is approximately 1.5 million.Taking the DN80 four-path transducer installation angle of 50° as an example, the mesh division result is shown in Figure 3.3.
Figure 3.4: Velocity Contour Maps at Inlet Flow Velocity of 10 m/s, Installation Angles of 50° and 30°
To better understand the fluid distribution inside the pipeline at different installation angles, taking the two cases of installation angles of 30° and 50° as examples, when the inlet flow velocity is 10 m/s, the velocity contour maps of paths one and three are shown in Figure 3.4.
FAQ
Q: Does the Structural Design Need to Consider Fluid Characteristics (Such as Viscosity, Bubbles, Suspended Solids)?
A: Very necessary, different fluid characteristics have different effects on ultrasonic transmission: High-viscosity fluids require stronger signal drive and receiver sensitivity design. Media with bubbles or suspended solids cause signal scattering, so higher SNR and signal filtering algorithms are needed. Therefore, the structure and transducer selection should be optimized based on the measured working conditions.
Q: Can the Design of the Insertion-type Ultrasonic Flow Meter Support On-site Real-time Monitoring and Remote Diagnostics?
A: Modern designs often integrate: 4-20 mA / Modbus / HART output interfaces. Self-diagnosis function (signal quality, fluid status detection, etc.). It can be integrated with PLC / DCS or IIoT platforms for remote monitoring and early warning, improving operational efficiency.
Q: Is the Insertion-type Structure Suitable for Large-diameter and High-flow Conditions?
A: Yes, compared to the built-in flange type, the insertion-type structure reduces the opening cost and is better suited for large-diameter applications. However, attention should be given to the following in design: Set appropriate probe insertion depth and angle. Use high-strength materials to support high-flow shear forces. Consider the influence of velocity distribution and Reynolds number on the measurement path.
Q: Does the Insertion Installation Structure Have High Requirements for Straight Pipe Sections? How Does it Mitigate Flow Distortion?
A: Yes, because ultrasonic measurements rely on a stable flow field, insertion-type structures often require upstream ≥ 10 D, downstream ≥ 5 D straight pipe sections to ensure the velocity profile is fully developed. In the design, the following can be used: Optimizing probe angle and position (α angle or sound path angle), Controlling probe-wall distance, Flow field correction plates or flow guide structures.
Contact our engineering team today for a complimentary feasibility assessment of your pipeline conditions and measurement requirements.
