AbstractAccurate flow measurement in the laminar-turbulent transitional flow regime has proven extremely challenging. Whilst there are numerous flow measurement technologies available for accurate flow measurement, few are used in laminar-turbulent transitional flow with confidence. This is because practically all flow measurement technologies are adversely affected by the laminar-turbulent transition. Varying velocity profiles and the unpredictability of when transitional flow will occur, has meant that many end-users of flow measurement technologies actively avoid the laminar-turbulent transitional flow regime.
This thesis presents a method to identify and potentially correct the effect of laminar-turbulent transitional flow on flow measurement technologies using high-frequency pressure loss measurements. A vast quantity of high-accuracy data has been acquired using the UK National Standards oil flow facility for laminar-turbulent transitional oil flow experiments. The author has demonstrated a potential ten times reduction in the measurement uncertainty by incorporating this pressure loss methodology with a prominent flow measurement technology. The measurement error for a turbine flow meter was improved from 2 % to less than 0.2 %.
Reviewing existing literature and classical theory for laminar-turbulent transitional flow revealed that flow models and theories do exist but to date, no practical approach has been documented for detecting transitional flow in industrial settings. This thesis presents a method for identifying, via high-frequency pressure measurements, and potentially correcting for the effects of laminar-turbulent transitional flow on flow measurement technologies. The fluctuations in pressure can be successfully used as a diagnostic to infer whether the flow is fully laminar, turbulent or transitioning between the two defined regions.
The critical Reynolds number of a flow can be determined from the diagnosis of the pressure loss data at high-frequency when monitored with respect to time. With sufficient resolution of the data, the swift transition between laminar and turbulent flow can be witnessed. This determination of the flow regime enables the end-user to measure the flow more accurately by applying the appropriate correction factor to their flow measurement technology. There could be one laminar and one turbulent correction factor for the flow meter. By incorporating high frequency measurements of the fluid differential pressure, suitable correction factors could be applied for laminar, turbulent and also laminar-turbulent transitional flow via interpolation. This theory has been applied in this thesis.
|Date of Award||May 2020|
|Supervisor||Janis Priede (Supervisor), Andrew Hunt (Supervisor) & Hoi Yeung (Supervisor)|