  In this article, we combine casting experiments and quantitative simulations
to present a novel multiscale modeling approach to predict local primary
dendritic spacings in metallic alloys solidified in conditions relevant to
industrial casting processes. To this end, primary dendritic spacings were
measured in instrumented casting experiments in Al-Cu alloys containing 1\,wt\%
and 4\,wt\% of Cu, and they were compared to spacing stability ranges and
average spacings in dendritic arrays simulated using phase-field (PF) and
dendritic needle network (DNN) models. It is first shown that PF and DNN lead
to similar results for the Al-1\,wt\%Cu alloy, using a dendrite tip selection
constant calculated with PF in the DNN simulations. PF simulations cannot
achieve quantitative predictions for the Al-4\,wt\%Cu alloy because they are
too computationally demanding due to the large separation of scale between tip
radius and diffusion length, a characteristic feature of non-dilute alloys.
Nevertheless, the results of DNN simulations for non-dilute Al-Cu alloys are in
overall good agreement with our experimental results as well as with those of
an extensive literature review. Simulations consistently suggest a widening of
the PDAS stability range with a decrease of the temperature gradient as the
microstructure goes from cellular-dendrites to well-developed hierarchical
dendrites.
