Bevelopment of PIV-based instantaneous pressure determination

Instantaneous planar pressure field calculation based on the velocity fields obtained from partical image velocimetry (PIV)measurement data is a new technique for the measurement of pressure field.Recent research results acquired in computation fluid dynamics and wind tunnel tests abroad have demonstrated the feasibility and significance of PIV-based instantaneous pres-sure determination.This paper presents a description of the fundamental operation principles of the methods addressing the different procedures for obtaining the local pressure gradient by local-ly applying the incompressible momentum equation (Lagrangian form and Eulerian form)and for the subsequent spatial integration to evaluate the planar pressure field from these pressure gradi-ents (an in-plane Poisson formulation and direct spatial integration).The influence of the viscous term in the incompressible momentum equation is discussed,with the conclusion that its effect on the local pressure gradient determination can generally be neglected and will therefore be omitted safely.In the second part of the present paper,some key technologies and current developments of the PIV-based instantaneous pressure determination are reported.It is revealed that the overall uncertainty in determining the error in pressure is dominated by errors in velocity measurement and thus the first key point to the success of determining the instantaneous planar pressure field is to obtain faithful velocity field from PIV as soon as possible.A comparative assessment of the Lagrangian approach and the Euleiran approach to determine the local pressure gradient is consid-ered,which would promote the use of the Lagrangian approach though they are found to have dif-ferent merits and demerits.For the two different methods to evaluate the pressure in a plane from the estimated pressure gradient,it is illustrated that the Poisson approach is clearly better than the direct spatial integration approach since the latter introduces a dependence on the inte-gration path and shows a ‘memory’effect in the marching direction.Finally,several potential research directions for the practial application of the PIV-based instantaneous pressure determina-ton are discussed,including the improvement of the velocity filed measurement from PIV,the i-dentification of the key parameters that need to be taken into account and the optimization of them,the innovation of the methods to obtain the pressure gradient and the pressure field itself, and the reconstrution of the pressure field in 3D flow and compressible flow,etc.